John deere 540a transmission has reverse but no forward.

[Rooney43]

Hi all, I've been reading on this forum for over 15 years but this is my first post.

I have a 1974 540A with powershift. We just changed the engine, clutch disk and rebuilt steering valve. Test drive went fine but then we realized that we no longer had forward. Only reverse. Changed the filters and they were ugly. Maybe crud got in and thinking some valve is stuck somewhere. Im at the end of my rope here.  I have the manual and pressure tests are next unless somebody helps save the day with a secret piece of information that Ive overlooked. 

Thanks for all the past and hopefully future info! 

[Green Man]

Could be as simple as the shift linkage not engaging the shift valve system. Likely lots of slop in the shaft linkage leading to the shift valve- or blocked for some reason. The shift valve has a 3 spring detent spool, arms in the front of the valve move the spool from mechanical shifting to the hydraulic spool position of forward, neutral, reverse. There is another spool with 8 spring detents for the gears. A mechanical limit system prevents reverse from going past 4 speeds. Make certain that you have 3 distinct F,N,R when shifting. Shift valves are busy with another shift manifold on the inside, about the size of a vcr tape. The manifold has 4 more small valves. Busy little thing x 10. I have to replace my system someday as I am missing some high gears. Just have not figured out how to get in there to do it yet. It is the same shift and trans system as the John Deere 4020 tractor.

[mike_belben]

I dont know the machine but in general tighten up what you can in the linkage system like green man was talking about.  Wallowed out clevis joints and hour glassed pins are no longer able to precisely position a hydraulic spool with any repeatability so your control pressures can be doing all sorts of unplanned things with age.  Its a good start.  


When you figure out how it works try disconnecting the linkages and moving the spools in small increments manually to determine if the issue is on the interior or exterior of the trans case.  And often its a bit of both.


After that id blow all the trash out, powerwash if you can, and want to see the inside of the sump to look for bits and pieces and huge sludge quantities from friction discs.  If none are found, obviously thats pretty good and tells us that its probably more a control/leakage problem causing low fluid force in the control segment, than a full mechanical failure.  Process of elimination.  Start with the links and manual spool positioning. See what it tells you.


Any leaks in the cooler circuit should be sealed up. That can be an issue. As can a cooler that doesnt flow. That oil probably comes back as drip lube.  Without it rusty stuff that shouldnt be rusty can hang up.

[dsroten]

I'll second wore out linkages.  There's a couple small aluminum levers on the side of the transmission and the holes will get wallowed out.  Mine are, but not to the point of not functioning.  My 540a only has 4 forward gears right now because the linkage can't travel far enough to take out the slack.  I ordered the little levers, but can't for the life of me figure out to remove them with the transmission in the machine.

[Rooney43]

Ok thanks guys for all the words of wisdom. It was the linkages after all. I asked my guys working on it 5 times.  They assured me it wasn't....until it was. Was reading the repair manual and forums for hours and hours. All up and running again. Thanks again

[mike_belben]

 smiley_blue_bounce

[thecfarm]

That is good and thanks for the update.

[Rooney43]

For sure. I wanted to express my gratitude and also I hate reading a whole topic and then op never fills us in on the actual issue found or resolution. Common courtesy.