I have a newly acquired money pit, A Komatsu D75s-3 S/N 10052. I really need some help before I go broke saving so much money doing it myself. It would pull fine cold, when TC got hot lost all drive, no turn to drive shaft, scavenge pump strainer had lots of aluminum on it. and would puke trans fluid out front seal when heated up. So I pulled TC and the pilot bearings were out and the pump and turbine had gouged faces, front seal was gone as well. I replaced all bearings and rings pump and turbine. After 6K in parts alone I put it back in and still have the same problem. The TC outlet pressure that leads to the cooler is below spec. My manual says 17 psi. At idle I have almost nothing, full throttle 10psi when I heat the TC oil pressure drops to less than 5 at full throttle. The machine will still drive at this point even with very little pressure leading to the cooler. The transmission pump pressure is 350 psi and holds well. My original thought was the scavenge pump pushed the oil to the cooler and might be bad but the manual says it is the TC outlet that goes to the cooler. I sure hope someone can help, I am at a loss now.
did you check the scavange pump?
Not sure how to check it, I did not examine it during the rebuild.
i had a similar issue with my d8h. it would push well until it got hot then it would flood the TC. so i pulled off the scavange pump and took it apart. the facings and bushings were totally wore out. put on a new pump and it's been good ever since. it was easy to pull off on my cat but am not sure how it is on your komatsu.
I think i can pull it easy. I will look at it. Thank you. Will advise.
I pulled the scav pump, looks ok. Bearings good, gears are tight, faces flat and no fluid came out of case when i pulled it.
Whenever you pull a torque converter that has been damaged, you also have to pull the cooler and clean it out. You also didn't mention what you saw and did to the stator. If the aluminum parts were damaged it is very probable that the steel stator also has some issues.
Thanks for the reply, I did a careful examination of the stator, it is aluminum on this machine it was fine, no scratches or gouges anywhere. I did clean the cooler, put in a new water temp gauge, thermostat. changed out every filter and strainer, flushed the entire cooling system. The cooler is not getting enough oil moving through it due to low pressure. Does the pressure for the cooler come from the transmission modulator or is it the torque convertor that creates the outlet pressure to the cooler?
The oil flow comes from the trans pump. The torque and later the cooler get whatever flow iis left after the clutches are filled. A worn pump, leaking seals or clutches can all reduce oil flow and thus cause overheating. Later Bob
Thanks Bob, The input to tranny from the pump is 350 to 375. The book says it should be 275. The output from tranny to TC is 50 Book says it should be 175. So the tranny pressure is too high and TC pressure is too low. My thinking is the modulator valve. Supposedly by the book when inching valve is activated it kills all flow to the clutches, when I depressed inching valve it had no effect on the pressure so wouldn't that rule out clutch leakage? I was going to pull the top off the tranny to get to the modulator, it looks like a bigger pain than pulling the TC. Am I on the right track or should i pull the tranny?
No don't pull the trans just yet. You seem to be doing okay with the testing but here are a few things the book might not have made clear. Pump or clutch pressure looks good and TC inlet looks too low. You can only get full TC inlet relief pressure with cold oil at start up. To get this, stall the torque when you start up. Then warm the oil up and check the trans pressure at high and low idle in all gears. If you have good oil flow the pressure will hold 90% of high idle pressure at low idle. Most TC overheating is lack of oil flow. The high pressures you have recorded may be someone trying to correct the problem on the cheap.If the pump pressure is good at low idle and the TC inlet pressure is still low the valve might be stuck open and causing flow loss. The inching pedal may have been put out of adjustment also in attempt to fix things. Later Bob
I did the test you described, at cold start had 50 low idle, 80 high on TC relief. At shift and stall it falls to 20 in all gears but first and it is about 15. The warmer it gets the worse it gets. I pinched off the return hose on the TC relief valve with a c clamp and it had no effect. Inching pedal had no effect stall or not. Pump pressure holds about 375. I really appreciate your help with this, I have a new found respect for heavy equipment mechanics. If it aint dirty it is tight, if it aint tight its heavy, if its heavy its hard to get too, and most of the time its dirty, tight, heavy and hard to get to! I am a small engine mechanic and I used to think I had it bad.
Wm. can you check the torque converter outlet pressure? Fit a gauge in where the temp gauge goes and it should get it. The outlet relief valve is just to hold a charge inside the converter. Normally inlet is around ,100 psi and the outlet is around 60 psi. Check both inlet and outlet, if the outlet is higher than the inlet at stall the torque is leaking inside. Most people would question my sanity for that statement but been there seen that. The torque under load is a pump and vortex action inside when loaded will pull the oil away from the inlet faster than the pump can supply it thus a lower inlet than outlet. The one I found this on had an iron sealing ring missing. Later Bob
Bob, Believe me, I thought I may have done something wrong in the TC too! The reading you are asking for should be the same as cooler inlet The hose goes right to the outlet orifice on the TC. Its reading was 10 cold, almost 0 when warm at idle. full throttle warm 10 full throttle heated 0. The TC inlet is 50 low 80 high. I am not one to ask for advise and not take so if you want me to read at the temp block let me know but it should be the same. One more thing, I am reading pump pressure at the tap on top of the transmission filter between the pump and transmission inlet.
Wm. I think you have checked it okay. Try to find the TC inlet relief valve and inspect it. I suspect it is either jammed open or has a broken spring. If it's reading low it could be letting a lot of oil flow dump into the case. When you get that fixed drop the pump pressure down to spec. From pressures TC in and out I think torque is together right. Later Bob
The relief valve looked ok. I pulled the cover off the trans, (boy was that fun) pulled control valves and found a tiny piece of steel shaving jamming the small piston on the modulator valve. I am hoping that was the prob as I hope to put it back together today. If it is, is it not amazing how a tiny sliver of metal can stop a 23 ton machine!
You not only have the metal debris, you have to undo all of the wrong repairs done, trying to make your machine work before you got it. Get all your pressures adjusted right first. Later Bob
I was wrong, that only helped but did not cure. The delay since my last post was in waiting for a new transmission pump from China. I decided my degrading pressure with oil warming had to be the pump, I installed the new pump and here is what I have: pump pressure is always 285 into modulator, with cold oil at start tc inlet is 120 at high idle and about what the manual calls for but at operating oil temp guessing 190F or so it is running 20-30psi. Unit still has good power at this pressure and if I didnt have a gauge on it I wouldnt know the difference. I dont want to burn up my very expensive new torque converter. Is this pressure Ok? Seems low to me. Thanks. What has been done: Rubber suction line checked Suction strainer cleaned TC relief checked, spring good, added 5 dimes to shim spring, did boost cold pressure only new pump scavenge pump checked, no oil buildup in case, less than a gallon when drained. oil cooler cleaned, each and every port
Okay Wm, if your tractor will move and push hard with oil in the 190 deg range you will not burn up anything. The red line for torque converter oil is 275 deg. The torque outlet oil is okay at 30, some machines only use an orifice not aa adjustable relief valve. Later Bob
Thanks Bob, I just want to clarify one thing, The TC inlet is running 20-30 psi, not the outlet. You mentioned the outlet pressure. And this machine does use a orifice.
Wm, the inlet is only as high as the outlet plus maybe 10 Psi at stall once the oil is warmed up. Check both and compare with full throttle in high gear brakes on. Later Bob