hydraulics question in general

[jay42782]

i recently bought a JLG lift from a guy needing a soleniod replaced..not a big deal.so he comes out this weekend to put the selonoid on and while testing raises the main boom and it wont come down.on the side of the machine are 3 manual release valves in case of pump failure.needless to say he cracked them to get the boom back down.while these manual valves were open he then raises the boom again and now i have nothing at all.no drive,tilt,telescope,steer... nothin!! my guess was he air locked the system.weird thing is the machine is equipped with an auxiliary pump wich overrides the engine pump and i still have no controls.

we tested all the controls with test lights and meters and there working as they should but no responce from the hydraulic side of things.we then tried several bleeding methods and still nothing.any suggestions would be much appreciated.thanks

[oneslogoat]

If the manual lowering valves were open then the machine should not lift as it should just dump the fluid back to the tank

[Badinfluence]

Just something to think about, Hydrolic fluid needs to be changed after any service. Contaminated hydrolic systems cause loads of issues. Anything in the fluid either gets trapped in the filter (if rarely equiped) or in the pump's seals and diaprams. I am not claiming this is the issue, but if the price is right flush the fluid.

Most of all don't get a car on it or get under it till you get it working! Safety first on that one.

[oneslogoat]

I've never heard of flushing a hydraulic system after working on it unless there was a huge problem that contaminated the whole system

[Badinfluence]

Most systems don't have a filter on them, that is why I was told that. It was just a general statement, that I have heard a few times over.

[jay42782]

Thanks guys.ended up being stripped out coupler splines.pump shaft was good.parts should be in tomorrow.I will udate after installation