955L Transmission Trouble

Hello

I have a 955L 85J4575 that I had the transmission rebuilt in. Actually the transmission that was in the machine had a bearing failure and just filled everthing in the transmission system with shavings and pieces. I had a parts machine with a good trans so I sent it out to be rebuilt before installing it in the good machine. My machine has a newer bottom, both finals rebuilt and a reman 13x engine so I thought it was worth it to have a rebuilt transmission. I had all the wear parts in the trans changed and installed a new oil cooler and new aftermarket trans pump. From day one the torque got hot. I talked to the rebuilder and they said it was probably the gauge. I had to keep the machine in service as it is my only loader, but only ran it about 100 hours. I was going to bring it in this winter to try to diagnose more but when I was loading it to bring it to the shop the torque converter locked up. I came to find that the bearing between the stator and the impeller siezed. Put another rebuilt torque in the machine and started checking pressures. The torque outlet was only at 20 psi at operating temperature stalled in 3rd gear. It is supposed to be 60. So I checked the torque inlet pressure and it was at 70 psi cold supposed to be bench set at 135psi so I don't know what that pressure is supposed to be at operating temp. After talking to the rebuilder they said to shim the torque inlet relief valve to try to get it higher. I shimmed it to get to about 130 psi cold at high idle. Again I don't know if this is correct since the book says bench test. Once the machine warms up it is down to 50 psi at high idle and the outlet pressure is at 37 psi. I have the trans pump on a gauge also while I am testing the other pressures and it is staying around 320 psi at high idle (within spec) and at idle it goes down to around 220 psi.

I have been in contact with the rebuilder and they don't know what to do. They are starting to blame it on the aftermarket pump and their recomendation is to go to cat and buy a new pump ($1650) and try it. That really isn't an option since it if it doesn't fix the problem Its not like cat is going to take the pump back. I have a hunch that there may be an internal leak that is causing the low pressure. I don't believe it is in the torque since two different torque converters have had the same issue (getting hot). Or possibly the pump is bad even though it is new but Cat will not test it unless they rebuild it.

I am kind of at a loss with this thing. I had $7500 in the rebuild not including the second converter which the rebuilder rebuilt for free. I know if I run it as it is I will be replacing the converter soon.

If anyone has any ideas I would appreciate them.

Thanks,

Phil

Leaks cause high temps
Running it will make it worse and wreck whatever you repaired.
Go thru the diagnostic procedure in the manual.
It will zero in on the problem very quickly as save time and money
The quickest way to bring hydraulic oil to operating temp is bleeding hi pressure discharge oil back to the sump

psuce1 said:

The torque outlet was only at 20 psi at operating temperature stalled in 3rd gear. It is supposed to be 60. So I checked the torque inlet pressure and it was at 70 psi cold supposed to be bench set at 135psi so I don't know what that pressure is supposed to be at operating temp. After talking to the rebuilder they said to shim the torque inlet relief valve to try to get it higher. I shimmed it to get to about 130 psi cold at high idle. Again I don't know if this is correct since the book says bench test. Once the machine warms up it is down to 50 psi at high idle and the outlet pressure is at 37 psi. I have the trans pump on a gauge also while I am testing the other pressures and it is staying around 320 psi at high idle (within spec) and at idle it goes down to around 220 psi.

Click to expand...

AFAIK the TC inlet pressure does not necessarily have to be set on a bench. Usually the pressure is quoted something like "no more than 135psi with cold oil at High Idle with transmission in neutral". I'm not sure I understand you correctly, are you saying the inlet pressure goes from 130psi with cold oil at HINL to 50psi at HINL with the machine at operating temperature, and your 37psi outlet pressure is with oil at operating temperature and the transmission stalled in 3rd speed..? If that is the case I would say that the most likely cause is that the pump is deficient. If you are measuring pressure at the inlet relief valve then you are effectively taking the converter out of the picture. The converter outlet pressure is controlled by an orifice therefore it is pretty much a function of inlet pressure, so if inlet pressure is low then outlet pressure will be also. With 130psi inlet pressure at HINL when the oil is cold I would be looking for something like 90-100psi under the same conditions with the oil at operating temperature.

I just checked the Service Manual for early 85J machine and according to it the pump pressure at Low Idle is supposed to be 310psi minimum and 355+/-12psi at High Idle. So your 320psi HINL is a 20-odd psi on the low side and the 220psi at Low Idle is extremely low. As the pump pressure is controlled by the transmisison control valve load piston how sure are you that the valve has either been rebuilt and/or is functioning correctly..? Maybe that's a place to start looking and confirm condition before looking at the pump.

What grade of oil are you using in the system..?

Thank you for the responses.

The machine is not being used in this condition becuase I am concerned that it will damage the torque again.

Since my initial post I have been working on the machine. I had a spare valve body around so I put it on the transmission which didn't change anything other than the pump pressure went up to 370 psi at HINL. The torque inlet cold at HINL was about 130psi and outlet was 55psi. Once the machine warmed up torque inlet went to 60psi and outlet was at 27psi. The next step was to change the pump. My parts supplier was nice enough to lend me another new pump to try out which I did and it didn't change any of the numbers so as far as I am concerned I have ruled out the pump and the valve body. As Nige mentioned the torque really cant cause this becuase it is orifice controlled. I guess it is possible the torque could be leaking which would cause the oil to dump back to the transmission sump which would never let it build pressure in the control valve, but is it possible that two rebuilt torques could leak the same? My last guess is a leak in the clutches somewhere but the transmission doesn't slip? Is it possible that the transmission could be leaking in one of the clutches just enough to lose oil volume to the torque but not enough to let pressure off that clutch pack causing it to slip? I am really at a loss here.

One question I have that I can't really find the answer to is how the torque converter pressure valve works in the valve body. Does the pressure have to back up in the torque from the orifice through the torque then up to that relief valve which would open at 135? If this is the case then the torque leaking could cause low pressure. Or does that valve somehow divert oil to the torque at 135 psi which would mean the torque possibly leaking would have nothing to do with the inlet pressure being low.

I am running Wolf's Head SAE 30 oil in the transmission.

Thanks again for the help

Phil

I think this calls for some input from our resident track loader experts. You need either Bob/Ont or tctractors to chime in on this one.

Reading what you've done since my previous post it seems to me as though the problem IS actually inside the converter. The only doubt I have is if the used transmission control valve that you installed for testing had the same issues as the one you removed. That is rather unlikely though.

The Torque Inlet valve is to protect the convertor from blowing up due to cold oil having restricted flow through the cooler. It is good on your machine, low pressure is from flow loss between pump and valve in my opinion. Take the filter base off and reseal it and tubes to valve. Look for cracks in parts too. Pump pressure should hold 90% of High Idle reading at Low Idle with warm oil on a good system.
Later Bob