Good morning, instructors, and welcome to the third in the series of our webinars for the AD Foundation. Today's series is a continuation of Tim and the hydrostatic drive service, the hydrostatic components. Tim, yesterday, went through the basics, so this will be more advanced level. I just wanted to thank you again for taking time out of your day, and hopefully, these webinars are providing some wealth of knowledge to you. We will be, after this webinar series, I will let you know that we will be sending out a survey to see the feedback, if these were helpful, what we can do a little differently. We will be offering a series next year on some different subjects as we get more into the components and build this program going forward. Additionally, I want to hear your feedback, and if you could let Lindley or myself know, the AD Foundation is probably going to, in the next couple of weeks, send a survey out to the instructors. This survey will give us a feel for, and we want to get this done by probably no later than the middle of August. I want to get a feel for what the landscape looks like for the instructors in our industry for the fall. Are you going back to school? A lot of this will be information that we can use as we look at distance learning. We are trying to get a better feel for that as we make some decisions going forward. We will share that survey with you, too. I think it will be helpful for all the instructors to see what folks are doing. It will take us about a week or so to put that survey together. Take a look. You will be seeing that coming in the next couple of weeks, and hopefully that will be helpful for the instructors. I would like to thank Tim Dell again for taking time to go through this subject with us. I hope everybody has a great weekend and enjoys this webinar. I'm going to pass it back over to Lindley at this point. Good morning, everyone. Thank you again for joining into the third installment of our AD Instructor Series this summer. Today's webinar, Hydrostatic Drive Service and Diagnostics, will cover Chapter 24 of the Goodhart-Wilcox Textbook, Hydraulic Systems for Mobile Equipment, and Chapter 14 of Heavy Equipment, Power Trains and Systems. With that, please let me welcome our guest, Dr. Tim Dell. Dr. Dell is a professor of automotive technology at Pittsburgh State University for the past 21 years. He is the department's diesel and heavy equipment coordinator. Dr. Dell received his doctorate degree in curriculum and instruction from Kansas State University, his master's of science in technology education from Pittsburgh State University, and his bachelor's of science in automotive technology with an emphasis in diesel and heavy equipment from Pittsburgh State University. Before I turn it over to Tim, I'd like to let those of you that are live with us today that you may submit your questions during the webinar via the Q&A tab at the bottom of your screen. This webinar is also being recorded, so you may watch or re-watch upon your demand. With that, I will turn it over to Dr. Dell. Thanks again for joining us, everyone. Well, welcome, everybody. We'll be discussing hydrostatic transmissions again today. Maybe just as another quick reminder, August 4th, I'll be discussing planetary gear sets. So for today, you have these books in your office, again, Chapter 24 of the Blue Hydraulic, a Goodhart Wilcox book, and Chapter 14 of the Yellow Powertrains book as well. So I'll do my very best to try to get this content covered in less than an hour. It's very challenging. Again, I typically take yesterday's one-hour subject, today's one-hour subject, and discuss it over the course of about five hours with the students. So first of all, let's jump straight into service of hydrostatic transmission. Hydrostatic drives, by nature, do not coast or freewheel. So what does that mean? That means that you can't easily push them. Basically, they're not designed to coast or freewheel. Now, it is possible that the hydrostatic transmission could creep. It could creep forward, it could creep rearward, and be cognizant that if we're talking about a closed-loop hydrostatic drive, it might not be for propulsion, such as if it's the input for differential steer, then what is that symptom? It might not be that it causes the machine to creep forward or creep rearward. It might be creeping, let's say, drifting to the right or drifting to the left, depending on how that transmission is actually used. So if it does creep, and if you are trying to get that transmission back to a true neutral position, typically, we're going to focus on two adjustments on the pump. We'll focus on a control valve adjustment, called the null adjustment, and then we'll also focus on adjusting the servo piston, or servo pistons, depending on the actual design of the hydrostatic transmission. So the first thing you're going to ask is, well, which one should I do first? For the sake of time, I'm just going to share, you always do the piston or pistons first before you do the null adjustment. We can elaborate on that later if you'd like, but for now, let's just say we always start with adjusting the servo piston. Now, you can see that on the screen, I'm saying, whoa, whoa, whoa, there's caution here. Let's be careful. I can't overemphasize the risks that are involved with doing this. So we have our students do this, but we take precautions, and it's a normal standard procedure that's done in our industry, but it is one of the most riskiest tasks that you're going to ask this technician to perform. So if you think about it, let's say it's an electronically controlled machine. You are now going to mechanically command this machine to lead neutral into a forward or reverse position, and so most manufacturers will say, okay, let's get this machine up on jack stands, and so we're not going to run over anything or anybody or cause a fatality. Now, you can see over here, I just got an illustration of a rubber track loader. If it was, let's say, a skid steer, you could have it off the ground, and then you might even go as far as taking the skid steer wheels off as well if it was a skid steer type machine. Bottom line is you need to take precautions that you're going to cause this machine to move. Now, the other thing to consider is if it's an electronic controlled machine and you're going to now mechanically make it to exit neutral, that is forward or reverse, if you have speed sensors, now you're going to potentially cause air codes, and so the service literature may or may not say to disconnect those speed sensors so that you are not introducing air codes into the system. Now, when we're going down this road, first of all, before you start thinking, okay, how am I going to fix this creeping forward or creeping rearward, there are two other potential causes that could cause this transmission to drift forward or rearward. One is if you have an old system that the actual mechanical linkage itself could be misadjusted and not in an actual true position, that would be the equivalent of it seeming like the operator is holding the lever forward or holding it rearward, so the old skid steer or swather type examples, those are complex mechanical linkages that are easily misadjusted and need to be set back to neutral. And then, of course, I'm very precise in how I'm saying this. You could also have stray currents to the actual solenoid that could cause it to leave neutral. So, when you think of stray current, most of us are saying, okay, this is a shorted circuit. We have voltage from somewhere else that's causing this solenoid to be electrified in that case. I actually have an example. This is an MT845 twin rubber track tractor where the ECM was at fault for actually causing this tractor to steer when it shouldn't, but I can't take the time today to go into all those details and explain how that occurred. So, first of all, if you're a little concerned that it's possible that you have stray current, first thing to do is just simply slide the coils off of the solenoids. And so, we know that you basically loosen the jam nuts and slide the coils off. You're not cutting wires and then basically restarting and testing the machine to see if that occurred. And of course, on that Challenger, that actually was occurring. So, I mentioned that we're going to adjust the servo piston or pistons first. This shows an example of a Bosch Rexroth cradle bearing design that has a single servo piston. In this example, you've got this cap on the end of the jam nut. You have a threaded rod that goes to the center of the piston. That threaded rod is attached to the spring. The spring is attached to the piston. And then, as you loosen the jam nut and move this threaded rod in and out, it causes the spring to move in and out, which then pulls along the piston in and out. So, in this particular illustration, you can see here's the jam nut, here's the Allen wrench. And so, as you're spinning this Allen wrench, it's causing this piston to move up and down. And then, of course, you've got this keyway that's pinned to the actual swashplate itself. And so, as you're making this adjustment and the piston goes up and down, it pulls the keyway up and down, which moves the swashplate into a forward and reverse position. Now, think about this for a second. When you're actually doing this adjustment, and if the machine is off the ground, it doesn't take hardly any drive pressure to cause an unloaded tire or track to spin. And it doesn't require much adjustment at all, very little adjustment at all, to cause this swashplate to lead neutral. And, of course, if you're working with students, you're knowing that they're going to provide multiple opportunities for additional learning that we don't necessarily always anticipate. So, what does that mean? One year in our lab, students were out there and they were cranking on this, and basically called me out there. This was not my lab, but anyways, I'm called out to the lab for somebody else's class. And they're saying, hey, we're spinning this, spinning this, and spinning this, and it's not doing anything. We can't get this pump to do it well. They basically moved this piston so far that it disconnected the actual piston to the swashplate. And in addition to that, they actually bent the feedback link and ruined it in that case. So long story short, it only takes just a little bit of an adjustment to take this servo piston and to lead neutral and come back to neutral, and we're trying to find neutral. So you could say, well, then visually looking at this system, how can I determine when I leave neutral? You can do it two different ways. You can look at the drive pressure on the closed loop legs, leg A and B, which we talked about yesterday. And you can also visually look at the drive axle, the undercarriage, the drive tire, and physically see it move. Both of them could potentially be hard to see. Like in other words, if the drive wheel was off, then you have a much smaller drive axle that's spinning. And so it's just, you have the opportunity to make mistakes here. And so I can't overemphasize how you've got to be careful when you're turning this Allen wrench that you're basically just doing it very, very little. Now on these adjustments, this is on a running machine. So this illustration just shows a pump that's on a stand, so it's a drive pump in this particular case. But this is actually on a live running machine, and again, you're causing it to leave neutral in this particular case. So how are you going to do it? In order to adjust the servo piston in this particular case, you have to take a hose and you have to hydraulically loop the servo pressure from the forward to the reverse servo ports. You have to basically loop those together. Why is that? Because on this particular design, we actually have fluid pressure on this side and we have fluid pressure on this side. And if you start cranking on this, now you are really going to put the system in a bind trying to overcome that fluid pressure. And so you have to balance that fluid pressure by looping basically the forward and reverse servo pressure. In addition to that, you also need to be measuring your closed loop drive pressure leg A and leg B. And this particular machine on this one, you have the luxury of measuring both forward and reverse. You don't always have that, and I'll explain that here in a second. The other thing we need to consider is if we don't have the machine on the ground, which you can't, you can't have it on the ground, you've got it off the ground, so it doesn't take very little pressure at all to actually cause this machine to move. And so you might be using a lower pressure gauge because otherwise you won't even see the needle move in that particular case. And so it's helpful to have a small pressure gauge on there, but if you accidentally apply the brakes and put some type of load on this actual machine, then you're going to stall the system and you'll very quickly break your gauge and break the needle. And so our students have, you know, damaged many gauges when they've actually been doing this test. Now, if you have a tetra gauge that basically measures low, medium, and high pressure, then that helps, but you again would need to have two where you can measure both drive loop A and drive loop B. So when this machine's actually running and you're doing this test, this gauge here and this gauge here, if I ask the groups here participating, what should those gauges read? You should say they read low pressure, specifically charge pressure when we're in neutral position. We could say approximately 300 and 300. And then when you basically leave neutral, it's possible that this pressure gauge on the drive side might only go up a little, maybe 360, 400. It might be a very little. And so if you have a very large pressure gauge on here, a 7,000 PSI, you're not going to see that actual change in pressure, and that's why a person's probably going to want to use the smaller pressure gauge, but got to be careful that you don't damage the actual gauge. So as I mentioned a second ago, when you're doing this, this particular system has the luxury of measuring both, and so if the student was doing this, the technician, instructor, whoever's actually doing this test, I would be simultaneously looking at closed loop leg A, closed loop leg B, and watching the drive wheel with this actually looped, I would be very gradually, gradually, gradually moving this Allen wrench, and we should see multiple things. We should see one pressure gauge basically go slightly up. The other one should go very slightly down, because we see that 20 to 30 PSI pressure drop, and then we should also see that axle spin. In that particular case, then you would say, okay, I've left neutral, then you would bring that Allen wrench backward, back past neutral, and then in the opposite direction, and again, then you would see, again, the pressure go up, and then the pressure go down, and the drive wheel go in the opposite direction, and then you would basically bring the Allen wrench back into the center position between those two points, and then you would say, I have indeed neutralized and centered that servo piston. Now, what happens if you do not have the luxury of measuring both closed loop leg A and closed loop leg B pressures? Well, it's possible that your pump only has a pressure port for measuring just simply drive pressure. So you're looking at a shuttle valve here. This shuttle valve says, okay, I'm looking at drive loop A, I'm looking at drive loop B, and I will send the highest of those two out to the pressure port, and therefore, we do not know. So this pressure gauge does not know if this is forward, it does not know if this is reverse, and it becomes a little bit more of a tricky task now of adjusting this pump. So this is off that MT845 Challenger for the differential steering pump. So we would have had a drive loop hose from the servo port of the forward and reverse connected together, and then basically, you would have your one drive pressure gauge on, the system would be running, you'd see, let's say, about 300 PSI, and then as you loosen the jam nut, here's how you would do this adjustment. You take the Allen wrench and you go in one direction, and as you go in one direction, you would see that the drive pressure goes up slightly, you'd see your drive axle begin to turn, and then you would mark on the actual pump, this is where we saw the pressure actually increased. And you would take the Allen wrench back to neutral, and then you would take it in the opposite direction, and in that process, from here to here, you'd see pressure gauge drop, and you'd see pressure gauge rise. When the Allen wrench reaches somewhere over here, you'd make a mark on your actual pump, and then you take your Allen wrench and you bring it right back into the exact neutral position and say, okay, my axle has stopped, I knew it went in one direction this way, in the opposite direction this way, bring it right back to the neutral center position and tighten the jam nut. Again, this is an example where we could not measure both drive movement leg A and B, we would only know that it is drive pressure. Let's go on to the next adjustment. The next adjustment would be the null adjustment, this is the control valve on the actual pump itself, and you're going to be centering the control valve. This adjustment is also very sensitive, and so on the actual null adjustment, you have a jam nut here, and you actually have what is an eccentric shaft that goes through the actual center of this control valve. When you're looking at it, you'd say, well, I think that's basically some type of bolt or a screw, it is not. When you put your Allen wrench on there and you're actually spinning this actual eccentric shaft, you can spin it around and around and around just continuously, 360 degrees, and the eccentric is located down here, and as you spin it, it's causing this spool valve to move to the right and to the left, and you're taking this spool valve out of a neutral position. Now, folks, I want to say in my corrected edition, which is coming out this coming November, not this November, but next November, we're going to rotate this servo piston to the left because technically it needs to be parallel with the actual solenoid, so that's a correction we're making. But anyways, this is your feedback link, and so as that servo piston moves basically to the left and to the right, it's going to cause the feedback link to move. It has a little pin that comes through here, you have these lever arms connected also through this spring. It's all working together so that as the spool valve moves, oil is sent to one side of the piston, the piston moves, the feedback link basically provides communication back to the system, and that's essentially kind of how it works. Now, here's the point, when you're making this adjustment, as you're spinning this eccentric shaft, it's causing this spool valve to move back and forth, and so it is incredibly sensitive when you're making this actual adjustment, and therefore it's another reason that you're doing it while the machine is running. So on this, if it was a live running machine, when you started at the very beginning, if it was close to neutral, we should have approximately balanced pressure ports here, and there would be a specification within, I don't know, 10 or 15 PSI, but I personally, when I'm doing this, I want them to be exactly in a neutral position. So after I've centered the piston, and basically I've taken that jumper hose off, I've basically installed low pressure gauges on here, and folks, I'd actually say these are probably a little bit too low of pressure. When I've made this test before, I've actually saw this needle get approached basically exceeding this pressure, so maybe 200 or 300 PSI might be better pressure gauges here. So basically you're just barely losing this jam nut, and when you turn this Allen wrench here, just barely, barely, barely turning it, once it leaves neutral, you're going to see one servo pressure go high, let's say 160, it kind of depends, and then you'll see the other pressure go back to zero. So then you would turn the Allen wrench in the opposite direction, and then you would see this pressure gauge go high, you'd see this pressure gauge go low, you would also see drive pressures respond accordingly, and you would also see the axle move, or the drive tire or undercarriage move, because you have caused this machine to physically move. And so what you're trying to do is balance that spool valve inside of this actual control valve, and the way it is balanced is by setting this pressure and this pressure to the exact same point. So you would be balancing them, in this case, it'd normally be around 40 PSI and 40 PSI. So if you have a novice technician or a rookie student, when you're working on this case, you have more opportunities for student learning. This has happened in our lab multiple times, and what happens is a student comes back, and says, hey, I have problems. They bring you parts in their hand, they've had the machine shut down, we've got oil all over the place, and they say, hey, I am sorry, Dr. Bell, I basically had this shaft came out of the actual machine, and now all of a sudden I got parts, and this machine is on a full forward, full reverse, and we got problems. Well, what happened? Basically, they've loosened this jam nut too far, and it allowed this eccentric shaft to basically come rocketing out of this control valve, and now you've got oil spewing out of this system, and this full valve is now basically, you know, full forward or full reverse in that particular case. So it's a good rule of thumb, if you have a dry pump, to actually have the guys come out here, physically take a photo of the system on a dry pump on a stand, and have them disassemble it, because there are washers here, and there's a precise way of getting this back to a simple correct position. It's just a good practice to have them physically get these parts in their hand and get it assembled correctly. Otherwise, if they're doing this, and they loosen this jam nut too far, then all of a sudden they have, you know, basically caused this thing to come apart, and now they're going to have to figure out how to put it back together, and they did not know how it originally looked at the beginning. So if you have, let's say, an old school Eaton manual type control, you also have a control valve here that you can adjust, and then you would have two servo pistons that you're going to basically have to set to a neutral position. So let's first talk about considering the manually controlled control valve, let's say on an Eaton, and there's other companies that have a very similar design. So first of all, you have this plug or cap that's on the end, on ours, at our school basically we have a set screw we have to remove, and then there's no way of really latching on to this plug, so we actually have to use a pair of pliers to back this plug out to gain access to get inside of this actual control valve. And so I've had to make this adjustment on a live machine before. I guess if it was me in a classroom, I probably would prefer to make this adjustment with the machine not running. Just in case somebody starts making this adjustment too far, you might be able to get into problems. I'm sure there are people every day that are making this adjustment on live running machines, but be super careful, you don't have to adjust this too far. On this particular example, it was a loader backhoe, it was not in a neutral position, but it was barely not in a neutral position, so you didn't notice it with the drive tires on the ground, when the drive tires were off the ground, you actually saw it creep a little bit. This is, again, the orifice, feeds oil in from the charge pump, provides oil to the control valve, when it's in a neutral position, it prevents oil from going to the forward and reverse servo pressures. So the other adjustments on this old school Eaton style is you have these caps. These caps are covering up your servo piston, such as your forward and reverse servo pressure. So this is a drive pump that basically has been disassembled, and this is the time to make this adjustment is when you're reassembling this pump. So when I have students disassemble this in the lab, I have them make a clear mark here, and also have them make a clear mark here, so that before they remove it, they can get this servo cap right back into the exact position that they originally have. Now first of all, you will want to remove basically these keepers, it's just a piece of light thin metal that basically is kind of staked into the side of this opening on this cap, that's going to help hold the actual cap in the correct position. When you go back together and you're threading these caps back into the original condition, then basically you're going to use some gauge bars here and use a depth micrometer to go all the way down into that pump and get right on top of the swashplate, and then you're going to go to the other side, and Eaton's going to say that tolerance of setting this side to this side is so precise that it's a half of a thousandths. And so I like to visit with a veteran technician out in Hutchinson Cants, B&B Hydraulics, take my class out there every year and let them tour that shop, and he tends to say, when I set this on the actual bench, that by the time I get it on the actual test stand, basically I don't have to make that adjustment again. When I set it on the bench, it's so accurate that basically when I run the actual machine, it's actually good. So if it wasn't, then I would want to shut the machine off and make some very small minor adjustments to actually get it back to a neutral position. So if we have questions at the end, I'll be happy to answer those. Let's go on to another potential issue that you can have on your hydrostatic drive, and that is you could have a shaft failure that fails too early. So you could say, well, what's an example? My idea would be maybe 1,000, 1,500 hour or 2,000 hour shaft failure on a pump or motor. If the splines wear out too early in that particular case, it's not the pump or the motor's fault, then you have an alignment issue. And so then you need to basically get out your dial indicator and make some precise measurements to find out what is out of alignment. And so if you're trying to find good illustrations for that, in the heavy equipment workbook, not the textbook, but the heavy equipment workbook on page 186, I provide several illustrations for how you can use your dial indicator to go out there and measure, find out what is not correct, and how you can actually make the adjustments, find out what is wrong. Now if that occurs on your machine, and if the shaft fails prematurely, this is a case where you simply just take that component off, let's say it's the motor or the pump, disassemble the pump or the motor, you put the new shaft in, you reinstall it, you recommission the system, which I'll explain here in a minute, and you're done. Now you could say, well, yesterday you said that if you have a failure in a closed loop transmission, you replace both the pump and the motor. That is if you have a catastrophic failure, and if one is severely worn, let's say the rotating group of the pump or the motor, because they feed the other. But if you just have a shaft failure, that means the system's not worn, the shaft was just worn. And so in that case, you're not replacing both the pump and the motor, you're just simply replacing the shaft. So let's say you've taken the shaft out, the pump out, you put the shaft in, now you need to put the pump or the motor back onto the system. Lots and lots and lots of hydraulic manufacturers and machine manufacturers will explain the proper way to recommission a system. And the person sometimes will say, what do you mean recommission? What they're basically are saying is how we get this machine back to its regular state so that it can be put back into commission. So ultimately, I've provided, let's say about 14, 15 different steps here on how to actually go through that process. This is the actual process. You basically make sure the pump and the motor case are full of oil, that you have a pressure gauge, specifically I'm measuring charge pressure when I'm putting this system back together. And then I got my hand on the actual key switch so I can actually kill this very, very quickly and that I have zero load on the actual system. So let's say you have a harvester and you can put the gearbox or a compact utility tractor, you could put a three-speed gearbox in a neutral position. That is zero load, you chop the wheels. Then you have the engine at a low idle, basically you've got the reservoir full, you've got the pump and motor case full, and then basically you're going to operate that pump by causing it to move forward and move reverse and you're circulating the oil through that closed loop very quickly looking at the pressure gauge. And upon immediately starting the machine, if I don't see that charge pressure respond as it should, then I'm shutting it off immediately. And if I'm overly concerned, I could even have the fuel shut off solenoid disconnected and basically just crank the system over a few times without burning up the starter to actually see charge pressure respond. But ultimately it's with the system unloaded in that particular case, manufacturer may say, hey, I want you to then replace the hydraulic filter as you probably know. It's helpful to basically know when the filter is bad by using the filter indicators and not necessarily intervals, but sometimes we don't have filter indicators and so we have to go by intervals. And so that's another long drawn out topic for today, which I don't want to get into unless we have questions at the end and I'll be happy to elaborate on that. So now let's get into diagnostics and diagnosis of hydrostatic drives. I've listed about eight or nine different type of things that we can deal with when it comes to diagnosing hydrostatic transmission. Some folks tend to think it's a little bit mysterious in trying to diagnose these systems and hopefully through this webinar, if you're one of those, hopefully you'll find that it's not too mysterious. So first of all, let's get into the first symptom that you might have that says that the system is overheating. And with any type of symptom that we're trying to diagnose, I for sure want my students to first ultimately determine, is it a functional problem or is it an indication problem? So for this, if we're worried about that, how do we know the difference? Well, we can just use an infrared thermometer and physically go out and measure the temperatures. If we find out that the temperatures are actually low, then we probably have an indication problem then we need to physically go out and find out why we have an indication problem versus a true overheating. Well you could say, well wait a second, let's have some rules of thumb. Well in that particular context, if your service literature does not tell you, then you could maybe say, okay, well let's use one rule of thumb that if the system is a hundred degrees above the ambient temperature, then indeed it's hot. So if it's 97 degrees outside and we are measuring temperatures on this machine at 197, then we truly do have a hot system. There are other places where they say we want the reservoir never to exceed 140 degrees. It could be different for industrial hydraulics, it could be different for this machine. It honestly kind of depends. It also depends where you're measuring. Are you measuring right at the case drain exit of the hydrostatic motor? Are you measuring at the cooler? Bottom line is service literature can help and also using benchmarks from other machines. But as good rules of thumb, maybe the reservoir oil, maybe the oil exiting the hydrostatic motor, basically somewhere between 140 to 200 degrees, depending on the machine and the application and the ambient temperature that we're dealing with. So one particular machine, as I was doing research and writing this book, said that its light actually is going to come on at 200 degrees Fahrenheit. So if you look here on this electrical schematic, the battery provides current to a relay, the relay is then going to then supply voltage to the actual warning lamp as well as the warning buzzer. And then it's the actual temperature switch that closes at 200 degrees Fahrenheit that provides the ground to both the warning lamp and the buzzer. And so if you go out there and you're measuring and you're nowhere close to 200 degrees Fahrenheit with your infrared thermometer, then you could say, well, we need to find out where we're getting this short to ground that's causing this to come on when it should not come on in that particular case. Whereas if it is 200 degrees, then it's not an indication problem, then we need to find out why indeed this system is overheating. Now there are four different things we can look at in terms of an overheating transmission. You can have a worn out pump and motor. Well, if you have a worn out pump and motor, you're going to have other problems as well. You're going to have machine performance, sluggish, low torque. You might have high case pressure, you will have low charge pressure, and you might actually be popping the seals on the pump or the motor, specifically the shaft seal. And so anyways, if you have a worn out pump and motor, then of course it could be overheating. You could have restricted oil cooler, specifically internally plugged, externally plugged, you could have a lazy oil cooler bypass valve that's on vacation, and you could have somebody that has incorrectly swapped your neutral charge relief with your flushing valve. So let's address cooling first. So if you have a cooling issue and you're not sure what's going on, then you want to investigate your actual cooler itself. So one of the best things we can actually do is take a couple flow meters or do a couple tests separately and use a pressure gauge. So let's say this is the flow meter. Let's say you did your homework and you know that this flow meter, excuse me, that this cooler is supposed to normally be receiving about, I don't know, eight gallons per minute. So in this case, when you hook up the flow meter here and you see eight gallons per minute and you see lower pressure here, you know it's not a cooler problem. Whereas if you know that the bypass valve is supposed to open at 60 PSI and you see zero oil flow here and you see your eight gallons per minute here, and now you see pressure of 60 PSI here, then you know the cooler is internally restricted and we are bypassing it and now we have a problem because we can't cool our K-Strain oil. Now maybe one thing I might talk about later, or I'll just try to address it now. Sometimes folks will use one method for trying to diagnose systems as, hey, I have high case pressure as a method for knowing that I have a problem. When you have machines designed that have filters and coolers both in the K-Strain line, this adds resistance. And so if you have the resistance of a filter, you have the resistance of a cooler, it is quite possible brand new from the factory that you can see as high as 45 PSI case pressure, which is not necessarily good. And so it's not always fair to say, hey, I got 45 PSI case pressure, I must have a problem. You first have to do your homework and understand the actual design. So here's more information about checking coolers, right? So back when I was at Case IH and I was working on the hotline, I had a technician call me and said, hey, I got a problem, Tim. Basically this hydrostats overheating, I've replaced the pump and the motor, and so I don't know, $8,000, $9,000 pump and motor's been replaced, and I'm still overheating. What can I do? Well, unfortunately, we found that his oil cooler bypass valve took a vacation. It was too lazy, and it was easier for the oil to take the path of the least resistance and go straight back to the reservoir and not through the cooler, and we had a very simple fix of replacing the cooler bypass valve, and he should not have had to replace the pump and motor, and so that was a very costly mistake. And because of that, there are many automotive aftermarket folks that will say, if you're putting in a new transmission in your car, you're not just putting in a transmission, you're putting in a new cooler and a bypass valve, because I don't want your old cooler and your bypass valve to cause my new transmission to fail too early. So keep those in mind, and there's some folks that will actually say you can't possibly clean a cooler back to its original condition due to the internal turbulence and turbulators that are installed inside coolers. I'm not going to go down the road, though, for now. Okay, folks, this is probably some of the largest amount of meat and potatoes of doing some diagnosis on hydrostatic drives. You go to any particular local shop in North America and say, talk to me about measuring case drain on hydrostatic drives, and you can get a thousand different methods for how to do it. And I guess I subscribe to the point that there are tons of mistakes and wise tales in trying to understand this. So let's start at the beginning. Let's say we have a single-path hydrostat, and this single-path hydrostat has one charge pump, one piston pump, and one hydrostatic motor. We've learned yesterday that, in this case, let's say this pump is, this charge pump is delivering 10 gallons per minute to overcome the leakage of this system. So that means this pump would be about 50 gallons per minute, this would be about 10 gallons per minute. So in this illustration, let's say that, basically, when we leave neutral, we're going to have the remaining oil go over the flushing valve relief, it's going to flush the oil out of the motor, it's going to come into the pump, and it's going to flush the oil out of the pump and go back to the reservoir. Well, let's throw some numbers out here to try to make sense of this system. Let's say that the pump has one gallon per minute of internal leakage. Let's say the motor has one gallon per minute of internal leakage. Well, if this is a 10-gallon-per-minute pump, right, based on its displacement and engine RPM, then that means we have an extra eight gallons per minute when we are moving that's going over the flushing valve. So you have eight gallons per minute dumping into the motor, combine that with one gallon per minute of motor leakage, now you have a total of nine gallons per minute leaving the motor, coming over here to flush out the remaining oil in the pump, combine with the one gallon per minute leakage in the pump, and now you have a total of 10 gallons per minute. So if you're at the school and you're trying to demo this to students, this is a great time to try to have one flow meter connected here, separate these lines and have, basically, one flow meter here, and you fire the machine up, you're in neutral position, your students will see I have lots of flow here in neutral. When I leave neutral, you'll have lots of flow here, and when we're left neutral. Here's the problem. Everything I've shared right now, that is not enough information. We still don't understand good diagnostics of understanding case drain flow. You say, okay, well, let's elaborate for a second. Let's say now you got a bad motor. Let's say that motor is now leaking tremendously. It leaks internally five gallons per minute. So let's start at the beginning, we have one gallon per minute leaking here, five gallons per minute leaking here, and then I could ask you, get out the calculator, how much is left over? Five plus one is six. What did this produce? This produced 10. So you have an excess of what? Four gallons per minute. I'm trying to do math and talk at the same time, but anyways, so now we have four gallons per minute here. That's leaking into the motor. We said the motor is leaking how much? Five. You put those two together, and guess what you have coming out here? You still have nine gallons per minute. So right now you're like, well, holy smokes, I don't know if I have the charge pump leakage here. I don't know if I have a lot of motor leakage here, and this is why it's a problem to do K-Strain leakage tests without knowing what you're doing. So here's a thing to think about. If you had separated the coolers here, excuse me, the flow meters, and you're measuring here and you're measuring here, and you do these tests, when the machine's running, if you have lots of oil coming out here, yes indeed, you know that you have a pump problem. That's a good test because you should have just minimal leakage here, and now all of a sudden if it has lots of leakage, you know this is not the charge pump because charge pump oil's coming over here, and you would truly have a bad piston pump in that case. The problem is trying to understand when you have a motor problem. Well, ultimately, you would know you have a motor problem by using charge pressure as a way of doing your test. I'm going to elaborate on that here in a second, but I'm also going to share right now at this point, there are still times when K-Strain is helpful, and specifically it is helpful when you have multiple hydraulic motors in a single charge pump. So you can say, whoa, whoa, whoa, whoa, back up, what application are you talking about? Well, let's say an old school harvester that has basically a hydrostatic transmission that drives one motor for the front axle, and then it drives two motors for the rear axle. In that particular case, you have basically one charge pump, one piston pump, and three motors. That's one example. We have a skid-steer simulator at our school. It's another example. In that case, it's dual path. It has a single charge pump that delivers oil to two piston pumps in a single housing, and then it has two motors with two flushing valves. Well, think about that for a second. If you separate all those and you have, let's say, the dual path on the right motor, the dual path on the left motor, and you separate those and use flow meters over there, and then you use a flow meter on the tandem piston pump housing, now all of a sudden, all of these separate case drains are a little bit more meaningful. If you say, well, how is a little bit more meaningful, then I would say, well, just give me some numbers. In that case, let's say your tandem piston pump housing has, I don't know, two or three gallons per minute coming out of it, and now your motors are sharing the remaining, I don't know, three or four gallons per minute. Well, in that case, it sounds like everything's pretty balanced at that point. But the point is, then all of a sudden, if you see one motor with lots of leakage, the other motor with very little leakage in the pump, now all of a sudden, this information does provide a little bit more meaningful information in conjunction with your charge pressure test, which I'm going to elaborate on here in a second. So ultimately, charge pressure is our best test for measuring poor performance of hydrostatic transmissions, and it's going to let us know when our transmission is failing, and we'll elaborate on that here in a minute. Now, a second ago, I said it's possible that you could have a transmission that's overheating because somebody has incorrectly swapped the neutral charge relief with the flushing valve in the motor. I guess the challenge is here, the average person may struggle to know that that is incorrectly been swapped. And so I'd say, how would you know? You'd know by two actual points. You would know, one, because the charge pressure did not drop when you left neutral. That is one case. And then you might know based on your neutral test. And I say that cautiously because let's take 10 machines that are designed exactly the same, come right off the factory floor, you've got 10 separate pressure gauges, you hook them up to these 10 different machines, and you put this machine in a neutral position. With those 10 separate gauges, 10 different people doing that test, I'm going to say it's quite possible that you're going to find 10 different measurements for the neutral test. And so one might be 300, one might be 305, one might be 295. And so the average person may struggle to know that it's actually just a little bit low in the neutral position. So what would I concentrate on? I would concentrate on trying to see, does that charge pressure drop 20 to 30 PSI as it normally should when you leave neutral into the forward or reverse position? Couple other quick notes when we're talking about charge, you'll see that there are some Eaton hydrostatic transmissions on the actual charge relief that'll have a number on it here at the school. I think I found one that said 24, that signifies 240 PSI, one that was marked 22 on the flushing relief that signified 220 PSI. If that's the case, I think that was on our Eaton machine. One challenge is when we're measuring that pressure, it's a lot higher than that. So if this is accurate, then I would say this is probably cracking pressure and not full flow pressure because on ours, when we're running it, it's probably much closer to 280 or 300 PSI based on when we're actually running the system. Hey folks, there is another example you could run into. This was one manufacturer that had a skid steer under light loads. It was overheating and they found that the flushing valve on both of the dual path drives was not opening. And so basically their solution was basically to perform fast figure eights, which would build enough drive pressure to unload the actual flushing valves to cause them to shift and basically cause it to cool. If that was personally my machine, it was sitting in my shop, in my house, and that was occurring, I'm not going to be goofing around with basically doing figure eights. I would probably adjust those flushing valve, spool valve springs. Manufacturer says, I'm nervous about doing that because I'm worried that it's going to get up to the right operating temperature in certain climates. I would monitor that, but anyways, that's just my own personal take on that particular system. At the beginning of this presentation for this webinar, I explained to you how you could have a drifting or a creeping transmission. And when that occurs, basically I said, we're going to focus on the pump. We're going to adjust basically the control valve or we're going to adjust the servo piston or pistons and get that fixed. Two things I'd like to share on this. One, if it's creeping for the life of me, I cannot envision any particular way that a hydrostatic motor could be anything in contribution to this problem. So we're exclusively focused on the pump. Second thing is, if for any reason you're having to take that pump off the machine and actually do some deeper dives into it to try to figure out why we can't set neutral or whatever and we get it put back on the machine, this is not a worn out internal rotating group. And so that means we're not replacing the pump in the motor. We're just simply fixing the control problem on the actual machine itself. Okay, this is probably the number one reason technicians are sent out to a hydrostatic transmission is because the operator, customer, the owner saying, this machine is a dog. It won't pull itself and it can't do anything. It's just a dog and it won't do its job. So first of all, notice that the symptom is for forward and reverse, right? So one manufacturer in their troubleshooting treaty, one of the very first things they said, well, first of all, as I said, let's first eliminate the engine. Ultimately, is the engine at fault? If you've got a weak engine, don't expect your transmission to perform well. So eliminate the engine, okay? That goes without saying this focuses on hydrostats today, we're not going to get into the engine. So manufacturer said, okay, first of all, go out there, it has a three-speed gearbox, put it in your high road speed third gear, apply the brakes, basically operate the transmission, push it all the way forward in a forward position or reverse position, and you should see that your engine's going to log down and if your engine logs down, guess what? You're done. You put your tools in your toolbox, jump in your truck, go home, Mr. Customer, your machine is operating correctly. Now notice I take a pause and I'm kind of cautious on this. Why is that? Because that's not necessarily a possible test for the machine you're working on. If your machine has an Eaton IPOR, internal pressure override, that does not allow you to log the engine down because internally you have a control system that is basically going to neutralize your control valve anytime you reach that high pressure and so you can't possibly log an engine down when the internal pressure override basically deletes oil from your servo valve. Boss Rexroth calls this pressure cutoff. I believe Sauer Danfoss Series 90, I think their system's a little different. They call theirs, I believe it's pressure limiting and instead of draining the oil from the control valve, they send oil to the opposite side of the servo piston and basically push the servo back to neutral. All three are neutralizing the piston when you reach a high pressure and so those are three examples where you can't log the engine down. It won't allow you. You could also have a design that has an ECM that's going to take a solenoid and basically prevent the actual transmission from stalling. Those tests possibly may not allow you to basically log the engine down. Okay, the other thing I want to just quickly share, you can have other hydrostatic design systems that you need to consider such as four-wheel drive. Guys, I could spend a lot of time going down this road for now. Ultimately, I want to just share two or three things here. If you have a four-wheel drive, let's say on a harvester, then you have additional motors which means additional displacement, which means lower pressure, lower heat, more torque, and it's just different. You can't compare apples and oranges here. How do you stay safe from making mistakes? Focus on charge pressure. Don't say, well, the machine is strong when I have four-wheel drive and it's not when I only have just the front drive. Well, that's a function of displacement. So there's a lot to elaborate there, but for the sake of time, I can't go down that road. A couple other things to think about when we're considering low power and forward and reverse, you can't overlook the oil. You can't overlook basically the pump inlet. I'm going to elaborate on all three and then I'm going to focus on charge and then we can also take a sample and look at the filter. So honestly, and then lastly, notice I'm not even getting to the high pressure release till the very end. A rookie novice technician, you send out to the machine and say, this thing is weak. First thing they're going to test is the high pressure relief valves. That's the last thing I'm going to look at. So when we talk about the reservoir, anytime you talk to anybody, they're going to say, okay, yeah, the reservoir is good, let's move on. I'll tell you, I had a technician when I was on the hotline, took me on a rabbit trail for three days, said the reservoir is fine. Unfortunately, the machine had a bad hydrostat, not bad. The hydrostat was weak. The hydraulic system was weak. You could say, what's the commonality? You have an engine, you have maybe belts that drive both pumps or a shaft, but outside of that you have a reservoir. And finally, I had to convince that technician, go check the reservoirs, like, oh, I'm sorry. The sight glass was basically a yellowed over and it's my fault. I had low oil. It's a fluid drive, you got to have fluid, right? I call this slide here kind of the hero slide. Why do I say that? Because in our world, it seems like to me, many, many, many manufacturers don't address pump inlets. We're all sitting in front of a computer today, and when we basically started that computer today, we typed on it, right? And so we provided good input to that computer and we expect that computer to have good output. How could you possibly expect a hydrostatic transmission to perform and do very, very well, unless it has a good input? Well, that good input is a measurement of pump inlet vacuum. So unfortunately, many manufacturers don't even address this, whether it's a hydrostat or hydraulics or whatever, and so therefore it's not in service manuals, it's not in service literature, technicians aren't trained on it, people don't know how to measure the test, and it's very, very simple, and it's very, very helpful, and I call it the hero because it's quite possible, I tell my students in the class, if you fully understand this, you might be out at a machine someday, you might have the field rep out there, you might have engineers out there, they might have did every test in the actual book to try to fix this system and still not know what's wrong, and you might say, hey, let's just check pump inlet vacuum and figure out what's going on. So as a rule of thumb, one, what's good and what's bad? No vacuum is best. If you start approaching seven to 10 inches of vacuum, that's a problem. So number two, how do you measure it? You get into this fitting right at, in this case, the charge pump, and you basically put a gauge there. Well, how do you put a gauge? This is the fitting off of one of our hydrostats, basically you remove the actual fitting, basically drill and tap, and basically put a tap there, pressure port, where you can install a vacuum gauge. Now, this is not enough information. You can't just say, go measure pump inlet vacuum. So how do you measure pump inlet vacuum? In this case, I would want to have wide open throttle and have the machine under a heavy load with a lot of flow moving through the system. Then you're going to see possibly a high vacuum. And so in that case, you might see seven, 10 inches of vacuum. If you see lots of vacuum, then you have to back up and find out, do I have a suction strainer plug, a suction filter plug, or the actual suction hose? So as some of you guys know, where would you find this? This is very common in the concrete mixing truck industry. This is a very standard procedure that they do all the time because you have 14 feet of hose between the reservoir and the charge pump, and that's why it's common operating practice for them to measure pump inlet vacuum. Lastly, folks, the most important thing we can do for trying to diagnose a bad hydrostat is to, that is for bad performance, both forward and reverse, is to measure charge pressure. And it's not enough information to work with our students and our technicians and say, go measure charge pressure. You know, when I was on the hotline, you know, that was one of the worst things you could tell a person. Watch your pressure. Go measure. What are they going to say? Oh, it's good. It's not enough information. How do you measure? What should it be? What's the machine conditions, and what should you expect? That is something we need to understand. We know in a neutral position, we should have the highest, specifically at wide open throttle. Well, a good and a bad transmission are both going to be good and neutral. So this is a good transmission and neutral, 300. A bad transmission, such as bad pump and motor and neutral, is still going to be 300 PSI. Again, these are the specs. This is what's measured. So I measure a good one's 300, neutral position is 300. Now, if that transmission is bad, when we start to put a load on it, technically, guys, it's going to be even less than 240. It's going to drop and continue to drop. And folks that I work with out in Hutchinson, they say it's going to drop even more. It's going to just puke and puke and puke and go down, down, down, and it's not going to recover because that closed loop cannot basically recover because we just have so much internal leakage. So we can also look at the filter. We can look for contamination. You'll know that when you study chapter 12, the contamination that I say, it's never a good idea to pull samples from a case and it's not even a good idea to pull samples from the reservoir. You want to use oil sampling valves, but this is the time when manufacturers will say it is a little bit more appropriate to pull a sample directly from the case because we're not caring about the oil in the reservoir or in the other locations. We want to specifically know what is inside the pump case and the motor case and maybe the case drain filter as well. That is sometimes a test that we can do. And lastly, what you can do is then measure dry pressure. Notice that's the first thing a lot of folks are going to measure. This is the last thing I'm going to measure. And so what are some of the things that could influence it? IPOR, which I said a second ago, pressure cutoff. You could have the crossover reliefs, foot and inch valve, anti-solenoid, manual bypass, lots of things could affect that. And so you got to address those, diagnose those, look into them, do your homework, cross your Ts and dot your Is. If you think you have a high pressure relief valve, a crossover relief valve that's bad, this is an actual test that you can do. Notice again that B&B Hydraulics, Hutchinson, Kansas, basically they just put in that crossover relief valve, turn it on, basically pump the system up and if it opens too early, then of course they know the crossover relief is at fault. Now what happens, you get to the very end of all these tests, you do all your homework, you check charge, you check case, you check everything and you find out, oh my goodness, everything tested okay. This is where it becomes not very fun when you're working with your customer. They're like, Mr. Customer, you're in second gear, you're asking for torque of first gear, so I need you to shift down to first gear and that's not a very popular solution. They may be asking for three times the horsepower, your machine has 200 horse, now you're asking for 300 horse. It's a matter of physics and you got to have some of those hard conversations with the customer explaining that the machine is performing correctly. On this slide, I'll just quickly say that if you have a machine that's sluggish only in one direction, this is the time to swap your crossover relief valves to check. Many of the crossover relief valves are set to the same pressure. Do your homework, look at the service literature, make sure the crossover reliefs are set at the same pressure. If they are, then you can swap it and see if that sluggish part goes to the opposite direction. If your transmission truly coasts or freewheels, then you have a poor performing worn out transmission and you're back to testing a transmission for poor performance, looking at charge pressure. The easiest test to diagnose is if your transmission will not move in either direction. In that particular case, we're looking at servo pressure. This is a machine that a graduate assistant brought to me, it was a low loader backhoe. He says it won't move in either direction. We basically connected servo pressure gauges on it, actuated the control valve, had zero servo pressure. I told him, good news. If your transmission has a plugged orifice, he took the control valve off, he found that basically he had some O-rings stuck in the orifice, and that's why we could not move this particular transmission. And so based on that, our orifices control the responsiveness of the transmission. If the orifice is restricted, it's very little response. If it's drilled out too large, it's overly responsive, so keep that in mind. One symptom you can also have is possible charge pressure is high only in one direction. That's the case you have a makeup valve that's leaking high pressure back into the charge circuit. I'll share with you, please don't ever try to isolate a hydrostat by capping off the pump, because if the motor has a high pressure release, then you're going to rupture the system. It's not a positive thing to do. And then lastly, guys, as we end this presentation here, if you're trying to understand how a hydrostatic test stand works, basically you have an engine or electric motor that drives the test stand pump, which drives the motor. The motor drives the pump in question and the motor in question, and then you have to have a pump on the end of that motor that you can load. So this is a photo I took in B&B Hydraulics in Hutchinson, Kansas. They have an engine outside that drives a pump. The pump drives this test stand motor. The motor is going to drive the pump in question. The pump in question is going to drive the motor in question, and then you're going to have all these pumps back here that you can squeeze off to actually load the system. And that's how you can test your hydrostatic drive. And then like I shared yesterday on the webinar, if you want to experience these things in person and be able to do some of this test in person and spend more than just two quick hours on it, then go to kccte.pittstate.edu slash industry.trainings. The first three workshops or four-day workshops are going to be December 7th and 10th, January and March. So, okay. Lindley, what questions do we have for today? Well, I'll tell you what, guys. We have maybe one. Let's see here. All right. We have a question from Dennis Massingham. I think I'm misconstruing his question. Is this presentation part of your three-credit AT-416 class, and how many contact hours? So, Dennis, our 416 class is our intro class. So there's a different colleague that teaches it. He teaches chapters 1 through 15 of basically the hydraulic book. That's the intro fundamental class. The 654 advanced hydraulics class is where I cover hydrostats. So hydrostats at Pitt State, we don't even really address in the fundamentals class. We don't have a dedicated powertrains class. So the advanced hydraulics class is where we cover hydrostats. And I spend about probably close to five hours in the classroom, in addition to demos out in the lab. And then, of course, students are disassembling pumps as well. So good question, Dennis. You're muted, Lindley. Thanks, Tim. Well, first, I wanted to thank Tim for your time. It's been a fantastic two-day presentation. And I want to remind all of our attendees of your email address in case they have additional questions at a later date. Could you go over that with them real quick? So that is tdell, so T-D-E-L-L, at Pitt State, P-I-T-T-S-T-A-T-E dot edu. Thank you, Tim. We might have one more question there. All right. Let's see here. Oh, Chris Thompson just wanted to say you did a great job. Thanks, Chris. Appreciate it. Hope the snow has melted where you're at. But in the meantime, if you have questions, you reach out to Tim. If you didn't get his email, contact me. I'm pretty sure you all have my email address. And I want to thank you all for your participation in the Instructor Series this week. And we're all really looking forward to seeing you again on August 4th for the next installment of Dr. Dell's webinar on – it's a hands-on planetary gear set. So it should be a wonderful day that we can all kind of work together, hands-on situation. And I wish you all the best of your weekend. And when you come to the next session, ensure that you bring a planetary gear set with you. That will be helpful in that particular case. So everyone, thank you very much for your time. And like I said, enjoy your weekend. And thank you for your participation.

hydrostatic transmissions

adjustment

diagnosis

servo piston

control valve null adjustment

caution

shaft failure

overheating

recommissioning

webinar