Th-400 cooler line pressure
I have rebuilt and installed my th-400 transmission in my 7.4l truck. I did many of the suggested modifications I have seen on threads such as heavier pressure spring, grind the 1/2 shift valve and plug the corresponding hole, dual feed the direct drum, disable the 2/3 accumulator, added needle thrust bearings, restrict the torque converter feed with a set screw drilled to .093 and i am using an allison low stall torque converter. I installed gauges to monitor my line pressure and cooler line pressure. I am running tractor fluid instead of dexron. My line pressures seem about 20 psi above stock in each gear and do not exceed 195 psi in reverse or low 1 which seems fine and expected. I however get about 70 psi on cooler line pressure until it warms up and comes down to about 35 or 40 in nuetral when warm. But while still cold, if I shift to reverse or low 1, the cooler line pressure is at or just above 100 psi. When warmed up, these pressures come down too. I have read that high cooler line pressures (100 to 119 psi} can cause thrust bearing failure on the crankshaft and that is why I have done all this work in the first place, I had the thrust bearing failure. Would running dexron have lower cooler line pressure while still cold? I'm concerned about another thrust bearing failure. I guess i can just always let the fluid warm up before shifting into reverse but don't like having to wait. Any input or ideas?
Last edited by revscott; 10-07-2012 at 09:40 AM.
Reason: capitilization of my I's