JLG 60HA does not power forward/back

[Bradc916]

I have a 1995 JLG 60HA. It has lots of leaks, issues, and otherwise but slowly I am rebuilding and repacking the cylinders. Right now, the biggest issues is DRIVE and moving forward and back. I have limited skills, but here is what I know so far...

1. The pump was replaced with a refurbished pump.
2. The boom lift, steering, rotate, tower lift, platform turn, platform level and all other functions seem to work.
3. The wheels are NOT in freewheel.
4. When I have put them in freewheel, I can rotate them by hand, so I do not think the wheel motors are bad.
5. I have ample fluid.
6. I have checked all the solenoids on the accessory valve body and the "dump" valve. They seem to magnetize when charged and they seem to be activating correctly.
7. When you trigger the controls to drive forward or reverse, the wheels (not in freewheel) rotate 2 degrees forward or 2 degrees back, but not enough to actually move.
8. I have a pressure gauge on the accessory valve and the pressure was adjusted as per the service manual for the top 2 relief valves
9. I do not have the correct hydraulic caps to follow the proceedure to set the DRIVE relief valve on the accessory
valve, so I have set the relief valve all the way "in" to max pressure while testing.
10. With a pressure gauge connected to the DRIVE loop at the back of the pump, I can see 500PSI as a constant pressure (no load)
11. When still connected, if I attempt to DRIVE in a direction, the pressure drops to 350psi or so.
12. I think the drive circuit should be 3200 PSI or so.
13. I swapped the control bodies on the vickers valve around. I took the controls for the TOWER lift functions which WERE working and moved them to the DRIVE section, and the drive section to the tower section. The DRIVE still does not roll more than a degree or two.

I may be forgetting some other things I tested. At this point I am at my wits end. Anyone have any good ideas?

 

[Bradc916]

For others: BOTH my level ground sensor and the boom position sensor appear to be junk. As a result the machine is powering the dump valve closes the waste flow and pressurizes the system. Now the machine rolls 1-2' and then bogs. Still troubleshooting but the issue from above was the two sensors failing simultaneously.

 

[Txhayseed]

Are your drive brakes releasing ?? Hydraulically released spring applied. I would check the pressure on your brake circuit. Putting the wheels into free spin doesn't test anything or mean much for testing purposes. Your manual pushing the spring and releasing the brakes that is all. I would check that first then check the null on your drive pump itself. Usually the null will cause an issue either forward or backward not both. But its worth checking since its easy enough. Those would be the two things I would check first. Level and boom position sensor wont stop you from driving. You wouldn't be able to raise boom past a certain point with a bad level sensor and a boom sensor along with level sensor either would keep you in low speed drive though.