Sounds like a problem with the forward clutch. Clutch could be worn, seals on piston could be leaking, or if power reverser, could be bad solenoid. Will need to do pressure testing to isolate the cause.
Pressures tested, only 100 psi at forward clutch test port,175 at reverse test port. But no cooling oil pressure. Does machine have to be at operating temp to get cooling oil to start?. It was -32c when I was trying to test. Spent 6hrs pulling out tranny and inspecting forward clutch piston seal and it seems to sit low in the groove, should it not protrude?. Fibre plates in both brake and forward packs look great.
thanks so today my fwd and rev pressure runs about 100 psi after about 40 minutes of use the fwd pressure will reduce down to 50 psi and tractor will stop pulling fwd but always back up
after warm if you idle tractor down it will have low pressure 30 to 50 psi and stop pulling reverse stays around 100
my tractor is mechanical reverser and no electric solenoids
some post say the pressure should be 150 to 175 psi but mine is around 100
on the front transmission port the psi is 200 until it warms up enough to leak off when driving the tractor fwd on that port if driving rev the pressure stays at 200 so apprears transmission pump is all good
You should list your tractor(s) in your signature.
I ASSUME you have a 6415, some guys post in threads if they have similar model (6420, 6410, etc).
For the JD 6415 TM 4648 is Operations & Test. TM 4649 is Repair
There is a pressure regulating valve for system pressure, but since you have lower pressure on forward than reverse, it appears you have internal leakage that will require disassembling clutch packs to fix.
Did you remove the piston from the drum and check the seals? Have you checked drum for any cracks? I would pull all valves from the housing and check for sticking valves or broken springs. ALso check for blown gaskets around any of the oil passages. The cooling oil can leak oil. Did you check cooling pressure? If it was too high, it will rob oil from clutch pressure. Did you check mfwd clutch pressures? Leaks in mfwd can also cause low oil pressure, also a worn pump can cause low pressure.