I’ve got a case 850B engine and torque converter rebuilt. It pushes good when it’s cold and shifts good for about 30 minutes then starts loosing pressure in high and low range and right hand won’t change from high to low correctly. Pressure will be in green in neutral then once shifted into high or low it drops to yellow. I have checked fluid, filters and screens which all are good. Any suggestions on what to check next?
Welcome to HEF Hank ! I'm surprised a Case guy hasn't chimed in yet, but I am sure they will shortly.
Welcome to HEF. I'm not a tranny guy but it sure sounds like something bypassing when the oil gets warm and more fluid. I'm surprised the case guys have not seen this yet either. It would help if you could edit your title to say something like "Case 850 dozer loses push when warm". Always helps to have a more descriptive title. Also helps down the road when someone else has the same problem and is searching the forum for answers.
There is a few things you can check - Pressure loss at operating temp could be a worn charge pump - was this replaced when the converter was rebuilt? What did the central hub & bushing look like in the converter? Was the bushing replaced? Hub worn on one side? Next, there could be broken oil control/hook rings on the transmission shafts. When these fail oil is sent to two different clutch packs when a track range is selected ie - RH low is selected & some pressure is sent to RH high. What this does is cause the packs to fight against each other while operating - like driving with a brake on. It usually causes transmission overheating & damages the clutch plates in the packs. If you click through each individual gear - at operating temp & at an idle - & watch the transmission pressure gauge & take notice of how long & how strong the engaging 'clunk' is, you will get an indication of where the leakage is occurring. A good transmission will have nearly the same pressure in neutral & when engaged & each range change will feel the same & take exactly the same amount of time. Forward/Reverse oil control rings are at the rear cover PTO housing. LH & RH High/Low are up high on the front cover - you need to remove the brake housings to inspect them....... If the oil control rings are broken - then it's likely the clutch packs are damaged ..... requiring a transmission overhaul to repair.
It doesn’t seem like there is any bindage or drag with the clutch packs when it’s hot
How about suction leaks? Is there a possibility air is being introduced on the suction stream aerating your oil? Foam don't work like fluid? I don't know the operation of your machine. It's just a guess. I know in some hydrostatic pumps there is a thermostat of sorts. Its job is to leak off control (charge) pressure to throttle back the pump. When the spring gets weak, it allows control pressure to leak off . This is common on Sauer Danfoss and I have seen in some Rex Roth applications.