JLG 40E boom synchronizing

[rookieatbest]

I have a JLG 40E that I repaired two hydraulic lines and now have the lower two booms out of synchronization. I bleed the lines prior to moving and when the bottom two booms elevate they go up, but when lowering the middle boom doesn't move in the down position. I tried the recommended manual lowering procedure by turning the descent knob counterclockwise and pumping the emergency handle. It was extremely hard to pump up and down. I then turned the descent knob clockwise and the pumping was much easier and the upper boom began to lower. I tried this as a test to see if the pumping of the lower and upper booms were different. Of note the upper boom works perfectly fine and I lowered it. The middle and lower booms go up, but when lowering only the lower boom goes down and the middle boom will "stick" in position and not lower. I know this wasn't the right thing to do, but I slowly unscrewed the plug on the block of the holding valve cartridge on the middle cylinder just enough to let it drip into a collection container. The middle boom slowly lowered over the course of the next 4 hours all the way to its resting position.

Before I attempt to elevate it again, does anyone suspect that the holding valve cartridge is bad? or some other issue that I can troubleshoot.

thanks!

 

[rookieatbest]

 

[willie59]

Welcome to HEF rookieatbest. :drinkup

Your best help at this is member Voodoomojo, our resident JLG expert, he checks in now and then and might be able to help with your problem. Be patient and stand by.

 

[VoodooMojo]

Just a couple questions to start:

Which two hoses were replaced?
There are reducer fittings on some cylinders that are needed to create a pressure difference to activate the counterbalance valve.

Did the problem happen immediately after replacing the hoses or after awhile?

Also, was it the counterbalance adjustment that was moved to let the boom lower?
If the valve was readjusted in any manner it will have to be replaced. There is no way to field adjust the valve.
We can try turning the valve back to its original adjustment for testing purposes but it will need to be replaced before anyone uses the boom. Death and/or Serious Injury can result from tampered counterbalance valves.

This machine has the "Red Knob Valve" installed on it for the boom syncronization.
Did you try pulling that while lifting the Lower Boom to see if the Mid Boom would react?


You can PM me and I will be happy to give you a phone number for you to call me so we can eliminate a bunch of typing and a few safety related issues.

 

[rookieatbest]

Thank you for the welcome...

The two lines that were replaced were
1. Hose number 33 on the parts diagram of the Mid Lift Cylinder
2. Hose number 36 of the Telescope cylinder going to TC on main panel

To be honest, I'm not sure if the problem existed before as I purchased the unit with the two busted hoses and was unable to operate the lower booms until the hoses were replaced. I have no leaks now and all other functions of the lift work.
I did not touch the counterbalance valves and they look to have not been removed by the amount of grime surrounding the fittings. The previous owner said they did not replace or remove those as well so I have to take their word for now.
I performed the Red Knob procedure and raised it to 6 feet then released the knob and the middle and upper fully lowered. Then I raised it again this time not pulling the red knob to about 6 feet. Stopped, then lowered and the middle boom is stuck at that position, but the lower boom fully retracts.
I'll PM you in a moment, Thank YOU!

 

[rookieatbest]

 

[rookieatbest]

It seems I'm too new to the forum and do not have the PM function active.

 

[willie59]

It seems I'm too new to the forum and do not have the PM function active.

You now have 5 posts, which is enough posts to be able to drop the probationary status and PM a member now.

 

[rookieatbest]

It works now Willie thank you however I believe he has exceeded quota limits. VoodooMojo has exceeded their stored private messages quota and cannot accept further messages until they clear some space was the message
I sent email in place of PM to VoodooMojo.

 

[willie59]

It works now Willie thank you however I believe he has exceeded quota limits. VoodooMojo has exceeded their stored private messages quota and cannot accept further messages until they clear some space was the message
I sent email in place of PM to VoodooMojo.

It happens. No worries, now that mojo has responded to this thread he'll be back.

 

[rookieatbest]

So I'm going to attempt to work on the mid cylinder sticking problem today and I'm thinking perhaps there is air trapped within that cylinder. I'm going to rebleed the lines again and hope I can resolve this. Also, if anyone can tell me where port "G" is? I wonder if the pressures are set on the corresponding values on the main assembly.

 

[rookieatbest]

The update, even though somewhat late, is that I had to replace two valves in the sync booms that were bad. Rebleed the lines and all is Great!!!!

However,......

The this one I think is right up VooDooMojo alley

The 40E is will not come out of creep mode.
I tested the switch as the potentiometer works at the lift. Turn slow and the booms slow, fast is fast.
The forward and reverse are a different story.
To start, I have two cells that were low in voltage. One was down by 2v and another by 4v. I tested with a total of 42 Volts.
Based on what Voodoo said in another thread on this forum I checked Pin 14 of the 17 pin at the motor controller.
My question is.
the output at pin 14 should be 5V and as the joystick is moved in the forward or reverse it should drop to 0v.
Being that the unit is charging and should reach 48 volt does pin 14 have a low pass filter on it that will supply 5V regardless of 42Volts or 48Volts?
Reason being is that I'm only getting 3.4 volts at Pin 14 and as the joystick is moved it goes to 48 volts and not 0V?
Is this indicative that the motor controller is Bad? and the main culprit that I'm stuck in slow drive creep mode with the booms fully lowered?

 

[rookieatbest]

Anyone???

 

[willie59]

Have you checked the upper boom and lower boom limit switches? I'm not real familiar with the 40E, but I'm near certain that when the boom is elevated (trips limit switches) it puts the motor controller (drive) into creep mode regardless of the position of the pump speed potentiometer, and if one were faulty it would take away that input regardless of boom position. I think the limit switches send an input to pin 4 on the motor controller to put the controller in creep mode.

 

[rookieatbest]

Hi Willie,
I checked both limit switches and they are operational. Voodoo mentioned the switch at the platform and I'm thinking that may be the culprit. When I rotate it counterclockwise I feel the detent position, but do not hear a click. If you go past the dent, it will continue counterclockwise. I'm thinking if it is stuck at the dent position, the controller will think it is to be in creep mode. Does anyone know where I can order the pot? I checked the JLG site and the pot looks considerably different.