I have 1981 JD 844, some has changed out the 955 cummins with a 855 big cam 4. Runs awesome. Transmission has never worked in 4th. Has been pulling like a freight train in1 thru 3rd. Now it it only puts well while it is cold. Soon a it runs for a little while it won't pull its own weight. Slipps like crazy. Oil is fresh Spirax TXM and new filter. Engine is having some over heat issues not sure if the transmission issues are linked or not. But today the engine wasn't even warmed(140) up when the transmission started slipping. I have some guesses whats going on but lets here from someone who has more experience with these hydrostatic transmissions.
Or does anybody know the easiest way to take the transmission out?
Interesting. That machine originally had a John Deere 8955 Waterloo built V8 engine or the 6101 in-line Deere built 6 cylinder. I would acquire the tech manual TM1189 and perform some pressure tests before I would remove the transmission. The cab has to be tilted to remove the transmission, again I highly recommend the tech manual mentioned if you don't already have it.
Correct, the V8 955 was replaced with I6 855 big cam IV. HP went from 250 -300 to about 400HP. I think what happened to 4th gear is they tore the shift clutch out starting from a dead stop in 4th. I am researching today the difference in ad-packs between the Hy-Gard and Spirax S4 TXM to see if that is the issue too. I have the service manual, but it more on clearances/ tolerances and exploded views of the components. No specs on pressures. I've only had it since the fall, completely rewired it, change all the fluids and filters. Like you say I should start with a pressure test, I'd do that both cold and hot.
Thanks MG never notice it before the cab tilts to the left, I may have to add a terminal block and cut the new wires on the right side of the cab. It looks pretty straight forward, and a whole lot easier than splitting it in the driveway. Tilting the cab I might have a beter view on where the transmission is leaking from. It is not leaking much and only while it is running. I have to add 1 -2 litres every 10 hours of running.
If you have the manual I mentioned, check section 90, page 9020-29 Transmission Testing and Adjustments. Pressures are there.