JLG 40H boom raise problems

Hi.
Looking for some insight. I have a jlg lift that I have owned for 10 years. This is the first problem I cant figure out. Lift will not raise from platform unless you start to engage drive to wither forward or reverse. You have to hold the drive just off neutral position either way slightly (not even enough to make lift move) and lift will only raise to 0 degrees or about 8 foot and then stops. It will not lift any higher. Also it will only do this much if you have toggle in high drive speed. Really acts like a low hydraulic pressure. As boom is extended out the lift will slowly go away due to more weight. Just didn't know if it could be electrical not telling a valve to open or close all the way or just a mechanical pressure problem. Any help greatly appreciated

Also. This is a for dual fuel lift. It has here pq controllers on platform. Also the lift up_down will not work from ground. When u go up or down from either you just barely see and feel the pressure being released one way or the other

butcherauto said:

Also. This is a for dual fuel lift. It has here pq controllers on platform. Also the lift up_down will not work from ground. When u go up or down from either you just barely see and feel the pressure being released one way or the other

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You could swap out the drive controller for whatever controller is closest and rule out the joystick. Doesnt sound like this is the problem but its an easy way to check. Also you can swap out the coils on the valves to rule this part out. If that isnt it i would be looking at the valve assembly. The name of the part is escaping me at the moment but it will be on the lift/ lower valve block.

barklee said:

You could swap out the drive controller for whatever controller is closest and rule out the joystick. Doesnt sound like this is the problem but its an easy way to check. Also you can swap out the coils on the valves to rule this part out. If that isnt it i would be looking at the valve assembly. The name of the part is escaping me at the moment but it will be on the lift/ lower valve block.

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Thanks for the feed back
I did change controllers with no luck. Also changed valve and solenoid from swing control with no change. Getting 5.5 volts to solenoid when commanded up. This is same as when commanded to swing. I did check today and only have 500 psi at lift valve when commanded up. However all other lift functions work fine

butcherauto said:

Thanks for the feed back
I did change controllers with no luck. Also changed valve and solenoid from swing control with no change. Getting 5.5 volts to solenoid when commanded up. This is same as when commanded to swing. I did check today and only have 500 psi at lift valve when commanded up. However all other lift functions work fine

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I recall us having a similar issue and the dump valve was the culprit.

barklee said:

I recall us having a similar issue and the dump valve was the culprit.

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Ok. I will check that. Is there just one dump valve for whole hydraulic system or one for each set of controls.

I think theres one for each circuit...

Do you know where they are located. I have the manual but maybe I'm just blind. Its got Vickers valves I believe. Is the dump made in the actual block where to raise and lower is or is it seperate?