PS works great, all other actuators very slow. Diverter good. Troubleshooting ideas? (JD750)

[chilly81]

I'm new to this with an old JD750. Trying to fix extremely slow actuators while the PS is working just fine. Pulled the diverter valve and it's clean and moves smoothly.

Have the JD manual and it's excellent explaining the circuits, but it's new to me so want to ask if it sounds like I'm on the right track.

• Every actuator is equally slow (ballpark 1/8th speed - with a few seconds delay to start moving)
• Every actuator holds position once moved and no external leaks.
• Power steering works great.
• PRV opens at PS full lock (by ear).
• The PRV opens when actuators deadhead/full extension.
• Fluid was terrible (water). 2 flushes, screens, filters in Dec. I pulled diverter today troubleshooting, it looked brand new, as did the oil.

So thinking what could possibly be wrong:

• Pump failing. But how could PS at full lock trigger the PRV (it's only 1gpm out of 5.7gpm) if the pump was flowing too low?
• Hidden crud. Trouble is, I can't think of how that would cause it to act how it is acting. Except possibly if it was on the suction line. Seems if it was the pressure circuit-it would trigger the PRV if it was this bad since it's upstream of the restriction. This is the part I'm probably most unsure about.

Next step is get pressure tester and see what I can see.

So long story short, I'm just trying to come up with a hypothesis and learn how it all works at the same time, so any advice would be much appreciated.

EDIT: I understand how the PS alone triggers the PRV now. So maybe it is just the pump wearing out.

 

[Dman1981]

Does this unit have a rotory piston pump

 

[chilly81]

Does this unit have a rotory piston pump

Doesn't look like it. It's like two interlocked gears that rotate and force fluid through.

 

[34Willys]

Are you certain the power steering and hydraulics run off the same circuit?
Patrick

 

[CloverKnollFarms]

Yah, I know many units have split pumps, one for steering and one for everything else. Looks like you tractor also uses two separate pumps

 

[Roadworthy]

If your three point is in the full up position and your rock shaft is not properly adjusted you could be running in bypass mode. Move your three point lever a bit off of full up and see if that helps.

 

[chilly81]

Are you certain the power steering and hydraulics run off the same circuit?
Patrick

Yes it is. I got the manual and traced everything out. It has a diverter valve that gives priority to Power Steering - taking 1gpm off of a pump that's 5.7gpm total. Took that valve apart and it looks nice and shiny and moves smoothly.

 

[chilly81]

If your three point is in the full up position and your rock shaft is not properly adjusted you could be running in bypass mode. Move your three point lever a bit off of full up and see if that helps.

I have a backhoe on it and there is a valve that closes off the rockshaft piston, locking it in it's current position (I think that's what it's for). I'll see if I can free the rockshafts to test that though.