JLG 40HA - tower boom syncro problems

[OFF]

We've got a JLG 40HA that the upright portion of the tower boom gets out of sync on. When stowed, that upright should be straight up & down, perfect 90 degrees to the platform deck. This one gets out a little, leans forward about 3 degrees after use in cold weather. When you try and correct it using the proceedure in the manual (take it up 6ft, pull the red button etc) it gets totally wacked. The upright leans even more forward and then the tower base section refuses to lower. Everything gets stuck up in the air. We replaced all 4 holding valves on the 2 tower boom cylinders and it made no difference.

Any special tricks or an idea what's going wrong here? :Banghead

 

[VoodooMojo]

Didn't you have a 60HA that did the same thing awhile back?
You swapped the hoses on the upright level cylinder and it came back into sync?

 

[OFF]

Didn't you have a 60HA that did the same thing awhile back?
You swapped the hoses on the upright level cylinder and it came back into sync?

Yea that was me. Same deal on the 40HA as it's big brother?

But what's that red "pull" knob under the control panel all about? It just messes everything right up. People who shouldn't be touchin things keep playing with it
and causing trouble.

 

[stone7]

This probably isn't it, but I've noticed that if the basket platform is over-level,
beyond level, toward the machine, toward the boom, --- a lot of things
don't seem to work right on a JLG 40HA. It won't go down all the way,
and other things seem to happen. I always tilt the basket about 30 degrees
toward the door, and then extend and retract the machine to reset it.

It won't cost you anything.

 

[VoodooMojo]

at the lower control station:
Pull out hold out the Red Knob while raising the Tower Boom about 6 to 10 feet.
At that time, release the Red Knob and Lower the Tower Boom to the fully lowered position.

If the Tower Boom will not fully lower, repeat the upper procedure.

OR:

Raise the Tower Boom about 6 to 10 feet.
At that time, pull and hold the red knob out while lowering the Tower Boom to the fully lowered position.
If the lower boom does not fully lower, repeat the raising it 6 to 10 feet and then lowering it with the red knob pulled out.

I would be fibbing if I said I could remember which of the two is the actual procedure. It has been awhile since I have done this.
Please let me know which so I can refresh my memory on this.

Either way, what is happening when the red knob is being pulled, oil is being diverted back to tank instead of the upright circuit.


There is a 2000psi relief valve in the upright cylinder circuit that will cause this issue if
the machine is used as a crane instead of a manlift.
Many times the machine will be used to move a welder, gang box, generator, pull an engine out of
a car, etc.

Or the valve may just need repair/adjust/replacing.

 

[OFF]

well we got it back using the old "voodooMojo switch hoses" trick. Worked like a charm, again, thank you. And we took the red knob off.

When that red knob is pulled, the top (upright) tower boom cylinder bleeds down completely. You can raise and go up, but when you come down it will only lower to the point where that upright cylinder run out of stroke
(fully retracted) and then the lower tower boom cylinder stops retracting also. That's when things get stuck up in the air.

I'll see if I can locate that relief valve. it's just weird that we've owned this machine since 1995 and it only became an issue in the last year. Overloading would explain it however. Cold oil would just make it worse.

 

[VoodooMojo]

It should be located at the upright assembly

I don't remember all machines having it.

 

[VoodooMojo]

.....When that red knob is pulled, the top (upright) tower boom cylinder bleeds down completely. You can raise and go up, but when you come down it will only lower to the point where that upright cylinder run out of stroke
(fully retracted) and then the lower tower boom cylinder stops retracting also. That's when things get stuck up in the air.....

I just reread your last post and wanted to get clarification.

Does the Upright come down all the way when the Red Knob is pulled when the engine is not running?

If so, the Counterbalance (holding) valve in the Upright Cylinder is suspect.
The Upright Cylinder Sync Valve (Red Knob) directs oil to tank when it is pulled.
If the Upright Cylinder comes down when the Red Knob is pulled without engine running, it means that the Counterbalance Valve (20) is not holding the load.

This is reason for concern because the load could be concentrated on the hose between the 2 cylinders and
not on the counterbalance valve.
The counterbalance valve's primary job is to hold the load in the case of a hose rupture.
At this point, if the hose fails, the upright can come crashing down causing serious injury or death to the operator or bystanders and/or property damage.

Securely support the Upright Assembly, Main Boom and Tower Boom to remove the load from the Upright Cylinder Counterbalance Valve.
Be EXTREMELY careful and verify there is no pressure trapped in the cylinder.
Remove the Upright Cylinder from the Upright Assembly.
Inspect or replace the Counterbalance Valves.
Look for debris or a damaged o-ring on the Counterbalance Valve.
Check the Cylinder Barrel for deep scratches, out of roundness or buldging.
May as well install a new seal kit at this time as well.

If you just want to remove the Counterbalance Valves from the cylinder withour removing the cylinder from the machine, be sure to pull out one of the pivot pins on the cylinder to ensure there will be no pressure in the cylinder.

 

[OFF]

No, that was always with the engine running and with the tower boom toggle activated in the up function while following the proceedure in the book that says, pull the knob, raise the tower until things looks straight, release knob and lower tower. repeat if nessessary.
We never got the call until the machine was way past the point of no return with the boom stuck up in the air inside a building. The top tower cylinder totally retracted while the bottom cylinder was fully extended. We ended up hooking a crane onto the boom for support and pulling all the holding valves to get it back down. Even then we had to use a come-a-long on the tower to pull it back because the weight of the boom was too far forward and things wanted to extend rather than retract.
First thing we did was replace all 4 holding valves on the tower boom cylinders - Thinking there had to be a reason they were messing with this "red knob from hell" in the first place.
I haven't let it out of the shop yet. I won't until I have an understanding of what the heck is going on. Only 5546 hours on this machine, not a lot really. Weather is not good right now, when it warms up again I'll take it outside and test it for a day. Everthing seems to be working normally at this point.

 

[VoodooMojo]

Thanks for clarifying that.