ford 640 series hydraulics

jds1956

New User
seems to work ok but bobs up and down a few inches with a load on it

anyone know what I should check to eliminate or help the problem

have checked some of the basics

it does this at any level the lift is in
 
Likely ram cylinder ring(s) leaking and it leaks down a bit & feedback sensing system detects drop in position & operates control valve to pump it back up to set position....this just keeps repeating, leak, make-up, leak, make-up.
 
Replaced the ram piston O-ring and back-up ring and most other O-rings that came with gasket kit
also the safety relief valve was replaced
Still have the same problem though
anyone know what else I may need to check?
How about the control valve and bushing it self?
Was thinking maybe some leakage by it due to wear?
The piston and cylinder it self looked to be ok
Don't know where I could locate these parts though to try and see if that helps unless I buy a whole new cylinder assembly which I didn't want to do due to the cost.
Anyone have any comments about this??
 
One of the posters here experienced that problem & posted this picture of the valve/bushing leak. He found a good used assembly.
 

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