JLG 40H Lift Drive/Brake Issues

[lee95]

I am having drive issues when you first start off it will drive perfectly and you might go 10' or maybe 100'. And it will stop instantly and will not move either direction all other boom functions still work fine. When I move the handle into drive position you can hear the motor pulling and it sounds like maybe the oil is going thru a bypass. Wiggling the wires by hand will not fix it but if I rotate the basket and or swing the boom back and forth it will start driving again and work fine for a bit and then does it again. I suspect the brakes are locking on as a couple of times it tries to move but is real jerky and then it triggers the bypass and stops. I assume there is an electric solenoid that sends oil to release the brakes but I don't know which one it would be. I do have the manuals but they aren't very clear at least to me.
This has the 425 Ford Engine. Any ideas of how to troubleshoot this would be greatly appreciated.
Thank You.

 

[willie59]

Welcome to HEF lee95. :drinkup

Does your platform control box have OEM controllers or PQ controllers? OEM controllers have a control lever sticking out of the control box and have a rubber seal boot on the lever, PQ controllers have a squarish block mounted on the face of the platform control and the lever is offset to one side of the block.

 

[lee95]

Welcome to HEF lee95. :drinkup

Does your platform control box have OEM controllers or PQ controllers? OEM controllers have a control lever sticking out of the control box and have a rubber seal boot on the lever, PQ controllers have a squarish block mounted on the face of the platform control and the lever is offset to one side of the block.

PQ controllers the controller for the drive is pretty old looking vs the swing and lift controllers which look new.

 

[willie59]

Well, it appears it really doesn't matter. I checked the diagrams for a 40H and it seems that model didn't use a solenoid valve to release the brakes, the brakes are released by pressure in the drive system. The hoses that are connected to the brake chambers should come from the over center (counterbalance) valves located on the underside of the frame. There doesn't appear to be anything electrical that controls or releases the brakes. I'm not sure what is causing the problem, the diagrams don't show any detail of how the counterbalance manifold works, no schematics, most likely some form of shuttle valve inside, maybe it's fouled up, but again, without proper schematics, I can't say what inside that manifold is causing the loss of pressure to release the brakes. :beatsme

 

[lee95]

So now I am wondering if I have a lack of oil flow and or pressure so I am going to try new filters and see if that helps. Thanks for the help. And yes the manuals are not very clear.