980G Transmission Pump Pressure Low When Machine In Motion After Speed Change

[YulMY]

Hye all

Details per below:

Model: 980G
Machine SN: AYT249
Engine SN: BET5197

Reported when on auto shift, after changing speed from 1 to 2, then 2 to 3 and so on, the machine speed did not increase. Suspected the clutch disc slipping and was confirmed since we can smell the burnt oil once opened up.

However, once we checked the trans pump pressure tap at the filter side, found that the pressure is 100psi, and only built up to 300+psi after a while. Not gradually. It stayed at around 100psi and after ~3mins it raises back to 300+psi. This is while stationary and neutral.

Tried testing the machine while in motion and by changing the speed manually, found that the pressure drops and did not rise back up UNLESS the machine is stopped (brake and machine speed slowdown). Brake used was either the drum brake or the clutch neutralizer. Happens to all forward and reverse speeds. When the pressure is back to 300+, machine runs fine and speeds up as per normal. Hence why when it was on auto mode, the pressure can't catch back up, which causes the clutch disc slipping. And here's the catch, this issue is intermittent sometimes gone after 20-30min which made me believe it's electrical.

The previous team has open up and checked+clean the control valves, and also replaced the transmission pump since there was some internal noise.
However, issue still persists.

Anyone else have encountered similar problem?
No fault code also when checked with ET.

The only thing that I can think of is the current signal sent to the solenoids not strong enough to fully open and engage the clutches? Or a faulty ECM?
If it's the clutch piston seals leaking, shouldn't it be unable to reach the spec pressure?
Control valve was open up and cleaned, so might not be the neutralizer valve, or a blockage. No external leaks too.

Any advice on how you would troubleshoot this.

 

[Nige]

Based on what you have posted.........

1. Is the problem worse cold or hot.?

2. Has anyone removed and inspected the pump suction screen located in the bottom of the transfer gear case.? An intermittent loss of suction could cause pressure issues. Also after your comment of burned oil maybe there is some clutch material in it.

3. When the control valve was opened up were the plastic orifices (I think there are 3) removed & inspected.? If blocked they are very difficult to clean, we simply used to replace them.

Attached the T&A for the transmission.

 

[YulMY]

Is the problem worse cold or hot.?

Feels like both similar. But have not really tested it thoroughly when hot.
Previously, the problem was intermittent. After 20-30mins, it's gone and back to normal. But once machine is off, and turn it back up again (immediately), issue came back. But this was few weeks ago.

Has anyone removed and inspected the pump suction screen located in the bottom of the transfer gear case.? An intermittent loss of suction could cause pressure issues. Also after your comment of burned oil maybe there is some clutch material in it.

Yes, when changing the oil, they inspected if there was any debris but found none. Not even during the burnt oil smell oil change. The bottom screen should be airtight is what you are saying correct?

When the control valve was opened up were the plastic orifices (I think there are 3) removed & inspected.? If blocked they are very difficult to clean, we simply used to replace them.

Asked the previous guy that opened up the control valve. He mentioned that there's like 2 orifices that was inspected and there was no damage or debris blocking it. They just changed the O ring that was on one of the screens.

Orifice checked PN:
8P9296 (more like a plug with small hole)
9W9831 (the one that the O ring was replaced)

The second orifice is similar to the ones on 980C control valves but different size.

Thanks for the T&A!

 

[Nige]

The bottom screen should be airtight is what you are saying correct?

Yes. If there are any air leaks whatsoever in the suction side and the pump "loses prime" for whatever reason it will lead to lack of pressure.

When the burned-smelling oil was drained did it look clear & bright or dark & cloudy.?

 

[YulMY]

When the burned-smelling oil was drained did it look clear & bright or dark & cloudy.?

Believe it was dark and cloudy. This was also near the supposedly scheduled transmission service.

Also, during testing the other day, they noticed that the transmission oil have bubbles, seen in the transparent glass at the transfer gear case.

We are currently looking for any signs of leakage or any point where air could enter.
Should not be pump failure since they've installed new trans pump.

 

[Nige]

Is there any chance that a gasket or O-ring has been left out of a joint somewhere when the pump was installed.? Oil will not necessarily leak out at that same spot if that’s what you are looking for.

 

[YulMY]

Hye Nige,

Thanks for all the input.

Has anyone removed and inspected the pump suction screen located in the bottom of the transfer gear case.?

Yes. If there are any air leaks whatsoever in the suction side and the pump "loses prime" for whatever reason it will lead to lack of pressure.

Because of this + air bubbles at trans oil, made me think of really checking the suction side of the pump.
After extensive checking, we found that the pipe linking the pump and the tank has small hidden crack right in between a hose section which caused it to be covered. Plus, it was right side up and under the machine which made it impossible to see. Only found it once felt by hand. No oil leak was seen there also since it was suction side and only air was sucked. Felt like a total amateur once I found this.

Covered the crack and tightened the clamps just to check if there was any difference in pressure. Found pressure build up was substantially better than before. Transmission even shifted normally as per previously when on auto.

Now we are replacing the crack pipe and changing the hose.

As of now we think this is the main culprit.

Thanks for all the help. Much appreciated brother.

Will update again once done and share if the issue is finally fixed.

 

[Nige]

I'm always glad when it's something simple.......