TB 1140 Slew Problems

[Hffhvg]

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…

 

[uffex]

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

 

[Hffhvg]

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…

 

[Hffhvg]

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.

 

[Hffhvg]

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

 

[Hffhvg]

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
View attachment 303723

Could these springs (15 in the picture) play any role? Should I also take this section apart?

 

[uffex]

Good day
Yes weak or short spring will allow initial leakage.
Kind regards
Uffex

 

[Hffhvg]

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?

 

[uffex]

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

 

[Hffhvg]

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?

 

[uffex]

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

 

[Hffhvg]

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?

 

[uffex]

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

 

[Hffhvg]

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.

 

[uffex]

Good day
See the attached explanation.
Kind regards
Uffex

 

[Hffhvg]

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.

 

[uffex]

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

 

[Hffhvg]

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.

 

[Hffhvg]

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

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.

 

[Hffhvg]

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.