640 Hydraulic Lift?

[Clay8Ns]

My 640 will not lift at all!The pump is primed but there is fluid splashing in the transmission in front of the gears.

 

[Dave in MS]

Transmission oil will move if the engine is running in neutral with the clutch out. Depress the clutch and see if it still splashes. If it does, you might want to check the hydraulic fluid level and see if it is decreasing. You could have a hole in one of the hydraulic tubes that passes through the tranny.

 

[Clay8Ns]

Your right about the gears making the oil splash!I've got pressure back to the top of the lift arm cover plate!I'm wondering about the relief valve or check valve at this point!What do you think?

 

[souNdguy]

Chain the lift arms to the axle, and put a gauge into the small 3x5 cover plate after you remove the plug.. lif thte arms and see what pressure you are making.. don't hold it like this as it really works the pump and relief valve over... use a 3000psi gauge for safety..

soundguy

 

[Dave in MS]

Clay, do as soundguy says and see if the pump is building pressure at the accessory plate. If it looks good there, remove the PTO selector cover and look inside the housing while the engine is running. Put the quadrant lever all the way up and looks for oil leaking from the piston end of the cylinder, or around the valve stems. If you don't see any leaks, you probably have a stuck valve. Post back with what you find and we can go from there.

 

[Clay8Ns]

Okay Guy"s!!I had to change the relief valve on the bottom of the housing and now the pressure is 2200PSI.Still won"t lift.No visible leaks inside.Removed the lift cover and put it in a vise with lift arms looking up.When I put air to it with the lift handle in the down position the piston will move.When I put air to it with the lift handle in the up position the piston won"t move.Also when the piston is fully extended and the lift handle is in the up position the arms will stay up and when it is lowered the arms will fall.Do you think the unloading valve is bad?

 

[Dave in MS]

Probably needs a good cleaning and a new O ring.

 

[Clay8Ns]

Removed unloading valve,o-ring worn,need to replace it.Must be a special o-ring.Having trouble finding the right one.Also removed the safety valve and the spring was broken.Need to replace it also.Are these o-rings a dealer only item?

 

[Dave in MS]

I'll go way out on a limb here and say that your broken spring is what is keeping your lift from working. While you are at the dealer getting a new spring, you can pick up the O rings and gaskets you'll need. Take the valves with you to be sure you get the right size rings. They are color coded, but the paint might be gone. Since you have the cover off, this would be a good time to check the clearances in the linkage, as well as the cam and it's follower pin for wear.