Hello masters! I have problems on my excavator regarding the slew not stopping. I got myself a manual and some measuring equipment like you already advised me. So the problem is that sometimes when releasing the joystick command the upper structure doesn’t come to an end. But not always. I did a test on the slew motor today according to the manual. I tested on the two ports that I circled on the photo. When using the control they both come up to spec at about 32MPa. When releasing they drop immediately to zero thats on the occasions when the slewing stops. At times when the slewing doesn’t stop the pressure drops from 32MPa to 20MPa, so there is still oil coming to the slew system, but I don’t really know how since I haven’t ever worked on hydraulics and this is my first excavator. I would like to know what to make of this and what would be the next step to narrow down the problem and come to the cause of it. And is the pressure dropping immediately to zero after releasing the control normal? Because when the slewing stops it always stops abruptly almost lifting the track on one side and I really fell like it’s abusing the machine…
Good day Stopping the slew motion is a question of the slew motor switching its function to that of a pump , pushing fluid under pressure. That only will work providing that the valves do not leak. Look carefully at No.13 and the seat these sit upon. Kind regards Uffex
I have checked the poppets and they both look good and measure at 24mm. The seats seem to be good too, since they sit in nicely with no play in any way. I wonder if the problem could come from the fine swing which this machine has. When the excavator doesn't stop slewing even the parking brake doesn’t engage, which I think it should…
So I have disconnected the cables as marked in the picture and it is doing the same, so I guess the problem isn’t coming from the fine swing section of the slew motor.
Here is a link to one video, maybe you will see that when I swung to the right and released the command that the machine stopped very abruptly in that direction and then again started slewing under its own weight. So if I understand this correctly the oil stopped coming to the slew motor for half a second because the machine did stop. Also when I leave the machine running when the slew motor holds position after a few minutes starts slewing again so that I can spin it around in any direction by hand. unnamed Watch "unnamed" on Streamable. streamable.com
Could these springs (15 in the picture) play any role? Should I also take this section apart?
Good day Yes weak or short spring will allow initial leakage. Kind regards Uffex
Hello! So I have checked the springs and they seem to be good. I decided to do another pressure test on E and D ports as marked in the manual. Now the results were after releasing the joystick and the slewing continued the pressure dropped immediately to zero. And when the slewing did stop after releasing the joystick the pressure stayed at 5MPa. But after the slewing stopped and upper structure holds its position and it takes about a minute for the pressure to drop from 5MPa to zero and after another minute at zero pressure it start slewing under its weight again. Should my next step be to take out the relief valves and check the O rings (6, 7, 9 in the picture) and check those?
Good day If the pressure leaks quickly and the check valves are good, the issue is most likely with the slew motor. You can make tests on the slew performance, it should stop in a reasonable distance in both directions. Plugging the lines with a gauge and compare the results will show up any issue with the main valve. Kind regards Uffex
Sorry for the late reply, I didn’t have time to work on the excavator. So today I have installed the gauge on the line coming from the valve block to the slew motor and plugged the hole on the slew inlet. When I give the command to slew the pressure gets up to spec at over 30MPa then takes about three to five minutes to drop to zero unless I negate it before by controlling the lever in the opposite direction, then of course the pressure drops immediately to zero like it probably should. Are these normal results coming from the control valve block? Can I narrow down this problem just to the slew motor?
Good day As I interpret your post the slew valve sounds good in the direction you made the test, if you can "T" connect the gauge into the line and with the bucket lodged into a trench conpare the results. Kind regards Uffex
I will try to do that, but unfortunately I won’t be able today. I came across one more observation today. I thought that at times when the slewing does stop it always eventually releases its position and start to drift. But with the machine turned off it doesn’t. It’s after starting the machine that it starts to drift immediately. Also when measuring the slewing overrun distance if I do it at full throttle the slewing always stops but at about 5-10 degrees so it brakes pretty hard, the only times that it doesn’t stop at full throttle is when the backlash from braking is so hard that it start to just drift in the opposite direction of testing. Is there any information to gather from these observations?
Good day Be sure you are following the slew function, when you slew left or right and release the lever the motor function will change to that of a pump, using pressure to stop the rotation of the superstructure. The parking brake will automatically apply, providing that the solenoid valve is deactivated. When activated, the brake will remain in the off position, allowing drift. Kind regards Uffex
I am following the slew function, it’s the change of function to a pump that stops the superstructure abruptly when it does. If it was the parking brake activating then I believe any other main joystick command would deactivate it which it doesn’t and the slew park brake shouldn’t apply in the same instant as releasing the slew function. As a matter of fact, I think the slew park brake never applies on this machine… What would be the steps to look into that? Also when you talk about solenoid valve being deactivated, which one are you talking about that would allow drift? I will try to T connect the gauge from the control block to the slew motor this week as you said so I will be sure that the problem is only in the slew motor.
Good day See the attached explanation. Kind regards Uffex
Thanks for this explanation, it makes a bit more sense to me now. I have been making some observations while testing the slew park brake and realized that the brake never applies when the machine is running. And while the upper structure is drifting if I turn off the machine the park brake does apply, but only after about 15 seconds (I guess this can be adjusted). As soon as I turn on the machine the upper structure starts to drift indicating that the slew park brake releases and again never applies until I turn the machine off. So regarding the slew park brake is it possible that the solenoids stay activated while the machine is running? Is there a way to check them or the pressure switches that activate them? As for the slew motion drift. I got into contact with the local guy that really knows this stuff. And it seems all these symptoms lead to the problem in the hydraulic motor like you already suggested… So I will remove the slew motor shortly and have it rebuilt.
Good day As I read the schematics, the brake should be on by default, only when you operate the slew (Left or right) can voltage connect to the brake release solenoid. The brake should remain off for a short period after the RCV returns to neutral, preventing damage to the slewing train. That part of your findings are as I would say is as it should be. If as I am interpreting your post the brake is not on when the RCV is at neutral would mean that the solenoid valve is permitting pressure to pass, releasing the brake or the brake is worn. That is not correct and needs attention. Kind regards Uffex
Thanks for all the answers and advice Mr Uffex. I will have the master that will service the slew motor have a look into this too.
Just a little update on this issue if anyone has similar problems! The last test I did which I should probably do from the beginning was case drain. The result was oil overflowing abruptly (like 5 liters in 10 seconds), which apparently is a clear indication that the problem is in the hydraulic motor. After I disassembled the hydromotor I noticed the fault immediately as the valve plate side connected to the cylinder block was worn out. I changed the valve plate only. The top of the cylinder block was a bit worn, but after checking it by measuring equipment the flatness was within the +\-0.01mm and pistons and holes were all within the standard, so I decided to just change the valve plate. Sure enough after reassembly now the slew stopping works like a charm. Even the abrupt stopping that sometimes happened before is gone. The only issue that is a bit concerning to me now is if I fully suspend the dozer blade and extend the boom and arm far away the machine will start to drift slowly again. I don’t know what to think of this, because I am new to the heavy equipment world. Is this drift to be expected when on a slope and all the weight if the boom, arm and bucket weight extended out to cause this drift? I haven’t done anymore testing up to now. I still have to look into why the slew park brake doesn’t apply while the machine is running. But I feel like this drift with extended weight on a slope could be caused by relief valves? Because with everything retracted the machine now holds the upper structure and stops normally.
This was the main cause of slew sometimes not stopping and starting to drift in my case for anyone wondering. If I analyze it correctly the bottom part of valve plate in the picture was letting the oil to escape.
So my slew park brake release solenoid is constantly being energized and the park brake never applies when an excavator is running. Anyone have an idea where the pressure switches would be located?
Good day The way to be sure follow the pilot lines for the slew, I have looked for a good illustration 27 the best I can suggest attached. Kind regards Uffex
So I found the culprit. One of the connectors at the bottom of the control block (I don’t know what section-command) was disconnected and “plugged” on itself. My guess is the previous owners did this because slew didn’t stop on its own, so they wouldn’t damage the ew park brake system if upper structure would drift. Now park brake engages when running but takes at least 15-20 seconds to engage… I think theres a time delay valve at the pressure chamber for park brake? Can that be adjusted?
Good day Sounds as if you are out of trouble. Kind regards Uffex
Hello! So am I able to adjust the slew park brake engage time by any of these?
Good day Why do you need to adjust the brake drain, those as standard do a good job? Kind regards Uffex
Hello. Because it takes for up to 20 seconds for slew park brake to engage. I do believe that 5 seconds is about a standard value?
Good day Have you the correct grade of fluid and be sure the fluid is over 50C, that is what the manufacturers will make figures for. Kind regards Uffex
I just changed the oil 5 days ago when I put the hydraulic motor back together. I put in VG46, which should be suitable for our climate according to the operators manual. I don’t know the exact temperature, but the gauge is in the green area when I am doing the testing.
I'm guessing the time delay is electronically controlled by the "on delay timer" in Uffex's post above. I'm not seeing anything in the picture you posted (post #25) that controls time delay. I'd be running through that check that Uffex posted above regarding pilot pressure in the slew circuit. Questions I'd be asking are: Is the pilot valve (joystick) leaking, or slow to drain when centered, causing a delay in pilot pressure signal returning to zero at the main control valve (where the pressure switch is)? Is the swing spool in the main control valve not centering properly (ie worn springs), resulting in the pressure switch still seeing pressure for say 10 seconds after you stop slewing? Is the anti-rebound/anti-reaction/cushion valve allowing bypass, which keeps the main swing working lines under slight pressure (enough to trip the pressure switch) when it shouldn't? Is this fault only noticeable when working on a slope? Is the pressure switch, delay timer and park brake release switch working correctly? Lastly, what is a flip flop unit?! I have zero experience working on this brand of machine, but answering the above questions might steer you closer to the problem.
Hello masters! So a little update on this slew problem. There is no more slew park brake issue, it works well now. After changing the valve plate there was still some drift on the slope in the slew function after releasing the command (the park brake now applies after about 5 seconds until then it drifts). The case drain test still resulted in about half a liter a second. Although the slewing got much smoother after changing the valve plate. This result bothered me a lot so I took apart the hydraulic motor again. I will be posting more pictures of parts in the next posts if someone more experienced would help me analyze them. The excavator had worked for about 15 hours in between. As I checked the state of the valve plate I noticed it started developing the same wear pattern as the old one. It was minimal maybe two 0.02mm deep grooves in the center top center between left and right kidneys, but I feel that is still a lot for 15 hours. I don’t have a picture of how the new plate wore down because I already lapped it to a flat surface. I marked it on the old plate with blue color of how it looked like. I notice that the wear on the old plate is almost symmetrical between left and right. I guess that’s why the drift is the same in both directions. And the same wear pattern is starting on the new plate, also drifting the same in both directions. Maybe it was my mistake because I didn’t lap the new plate and the cylinder block so the two surfaces weren’t flat to each other? I am pretty sure this is where all this oil is escaping via case drain. Is there any other common problem that could cause some misalignment between these two components? I am waiting for new bearings now. The needle bearing at the top felt like it had a lot of play. And the roller bearing at the bottom you could fell some “clicking” by hand when rolling and not turning smoothly. The holes in the rotor have no significant wear on surfaces as well as the pistons. I measured them with micrometer and the clearance between them is 0.025mm. Manual says clearance of 0.04 is level of concern. Pistons also pass smoothly through.
There is wear on the faces of piston shoes that could probably cause some case drain but I am not sure about that. They glide smoothly on the swash plate and when I disassembled the motor it felt like they stick to the swash plate like a vacuum. The swash plate looks like it has scratches but can’t feel any wear on it. The surface finish measures at Ra0.038 which is crazy accurate. It also rotates smoothly in the housing seat. The play between pistons and its shoes is non existent.
Here is also a video of how the slew behaved when the new valve plate was installed. Ignore the comments of slew park brake, the video is a month old and the park brake works fine. Uffex was right again. The oil wasn’t at the right temperature when I was testing it.
So I got the parts today. It seems that previous owner was changing the bearings and put in a shorter needle bearing to the brake valve. The original part from Hitachi seems 8 to 10 mm longer than the one that was installed up to now. Could that make the shaft with the cylinder block-rotor be misaligned to the brake valve and valve-port plate? Causing this distinctive one sided wear?
PROBLEM FIXED! (At least I hope) I will just put this update here if any poor soul has similar issues. With the slew drifting in my case the problem was in the hydraulic motor. First I checked al the valves and poppets on the brake valve. I also checked the pressure and how it drips so I was sure the problem isn’t coming from the control valve or anywhere else (all of this stuff I learned pretty much from this forum, I appreciate all the help). After checking the case drain it became clear where the problem was since it was overflowing abruptly. I had the motor apart three times. First I only changed the valve-port plate. It was in a pretty bad shape. Other components seemed okay, the pistons with the cylinder block were in a tight tolerance and pistons had no play between the shoes. By changing that part I can say the problem got 50% fixed (the drift wasn’t as apparent). Second time I changed the bearings and the seal to the reduction gears. The needle bearing was shorter than it should be and the roller bearing wasn’t installed correctly by previous owners. I carefully inspected the shaft also for any eccentricity. There were none. The second time I also lapped the valve plate and cylinder block which I didn’t know you should do when putting it back together. This time it seemed the problem got slightly worse. The drift stayed the same but there was some pretty hard shaking and gurgling sounds at the start of the slewing command. For the third time I ordered the new valve plate, cylinder block and the pistons. I found out that the old cylinder block was already ground town too much (compared to the new one the sliding surface was short for 1mm). Comparing the pistons the old shoes were pretty worn down at the bottom (about 0.5mm of material missing). For now I have to say this feels solved. The drift is gone and the operation of the machine feels much smoother. The slewing command is very responsive and feels much more powerful (expected if you think that the oil was escaping before). Thanks for all the help through this problem. I learned a lot with this one and got some basic knowledge of how my machine actually runs. Never would I ever think that I would ever see a hydraulic motor apart let alone fix one. But with all the help and information I gained through this forum I got it down. I really appreciate that.
Hello! So after about 100 hours the slew/swing hydraulic motor is starting to drift again. Also much lower power. When checking the leakage to the right is gushing out with oil, when checking left the leakage is smaller but still not up to spec. I don’t have the motor apart yet, but my assumption is that the valve/port plate will have this one sided wear pattern on it as always up to now (this will be the third time I will have it apart now). Other components will probably be fine. Does anybody know what is going on with my hydraulic motor? I am pretty sure that I always assemble it back correctly but you never know. I am comparing my problem with this article: https://www.hydraulicsupermarket.com/hydraulic-pump-failure.html According to it this wear pattern indicates improper assembly, focusing on the valve plate. Except in this article the one sided wear is more noticeable on the cylinder block/rotor. I also don’t think my oil is contaminated as there would probably be different more evenly distributed wear on the components. This is how the valve plates look like every time I disassemble the motor:
So I finally got my slew motor to a perfect working condition. Seems like the disk springs pushing to the cylinder block lost some tension and the spline on the shaft was a little worn probably causing some offset. Changed those and after that there was still some drift in both ways and case drain leakage was a bit high but up to spec according to my manual. Drift got worse as oil got hotter, but pressure was also up to spec so I knew that relief and check valves should be okay. I wanted to leave it that way and just accept that my machine has 12.500 hours on it and probably with those hours things like that can’t be fixed. It was also the fourth time that I had the hydraulic motor apart and I was done with the whole disassembly and assembly of it. Also this time of having it apart the drift was the same. Only leakage got better. But I couldn’t get the idea out of my head that with all these parts changed that no real improvement was made. I also noticed that the bores on the cylinder block to the pistons tolerance was out of place in some areas but mostly okay. On the old cylinder block the tolerance was tight through the whole length of the bores. So what I did was I had the old cylinder blocks contact surface ground down minimally, took the motor apart fir the FIFTH time, lapped the valve plate to it’s surface (this time there was no noticeable abnormal wear on it) and put everything back together but this time with the old cylinder block. Sure enough that eliminated that last bit of leakage and drift. The leakage now measures at about 0.2 litres per minute, which is even bellow the spec in my manual. Literally just a drizzle either with the motor in continuous motion or prevented from rotating by fixing the bucket in the ground. The drift is now only noticeable on extreme slope with machine additionally lifted with dozer blade and hoe attachment completely extended from the machine. If I have the hoe attachment about halfway from the machine no drift can be seen even in these very steep conditions. But I guess that even on new machines there would be just slight of a drift present in such extreme conditions since these piston motors are designed with minimal leakage for lubrication so there will always be some oil escaping and cause some drift with that much strain on the hydraulic motor. Anyway with case drain leakage that low I do believe and hope that this slew motor won’t need another rebuild quite soon. So I am gonna say that this problem has finally been fixed! Here are the videos of the current drift and case drain leakage: