JLG 600S Boom Shake

[Surfcharlie]

Anybody here have this problem and a solution for a fix?
I have several JLG 600s when full up and boom out shake violently when retracting back in. It doesn’t shake when the boom is angled between 55-60 degree. We have checked the torque on the cables, installed new pads and cleaned the surface on the boom. Also changed the personalities to slow the descent from the basket which works from the basket but not ground level. This slow descent is also not within the parameters (it’s 3x the time it’s supposed to be) set in the manual.

 

[Moonlite]

Whats your serial number ?

 

[Surfcharlie]

Here's one for a start 0300063869.
I have another in right now but I can't read the #. They both have the same issues.

 

[bcubes]

It sounds like you are experiencing counterbalance valve chatter on your machines. With the boom fully raised the weight of the mid and fly boom telescoping in is causing the pressure on the retract side of the cylinder to drop to the point the counterbalance valve closes until the pressure can come back up. To see if this is the case turn the function speed knob down to turtle and telescope in from the fully raised position. There should be no shaking. Turn the speed knob toward rabbit and the shaking will return as you get closer to the rabbit position. To fix it you'll need the JLG analyzer and the Service Manual so you can time and set up the functions speed properly. A word of caution. DO NOT attempt to adjust the counterbalance valves. These are factory set and if you feel they are bad replace them. But I think if you set the function speeds properly the shaking will go away.

 

[Surfcharlie]

We’ve changed counterbalance valves on one of the JLG’s and same result…shake.
We’ve changed the personalities on them as well just the point to slow the retract and take the shake out, but the retract is extremely and painfully slow. At the ground level not only is the retract slow the extend is slow as well. Not really a problem with us (mechanics) but will be with the operators when they call it in as a maintenance problem. To top that our QC will not pass it because the book has retract times listed and if it’s not to specs, they will kick it back. We’ve contacted the JLG tech and we’ve done everything he suggested and still no good results. He implied that the age and manufacturing of those year(s) models were mainly the problem. So I guess last resort would be to replace the entire boom assembly unless we can have the retract times in the manual changed or worded somewhere in writing to be acceptable.
If you have any other suggestions pass them my way and thank you for your help.

 

[VoodooMojo]

Have the top wear pads at the pivot end of the booms been lubricated? If not, try applying a non-debris accumulating lubricant (graphite or silicone base) to the inside of the booms they run in.
The volcanic dust can create tons of surface tension.

Set the main pressure relief valve to 3000psi before continuing. If already at 3000psi we can move on.

You can monitor the hydraulic pressure at the MP port of the main function manifold while the booms are extending and retracting.
Set the boom extend and retract speeds to normal range.
Extend the boom fully while in a horizontal position.
With a 0 to 5000 psi hydraulic pressure gauge at the MP port, monitor the pressure while extending the boom.
While still horizontal, retract the boom and note the pressure and pressure fluctuations while retracting.
The pressure is more than likely building up to 3000psi (main pressure relief setting) and dropping off to 230psi (load sense pressure) every time the boom jerks, and repeats. This is typically the result of surface tension of the boom.
There is a Load Sense Cartridge in the manifold that supplies pressure when demanded and spews it back to tank when not needed.
When the boom is not budging, the load sense valve is wide-ass closed causing all the oil available to flow to the flow control valve and telescope cylinder, the pressure will build up until it exceeds the mass of the boom and the resistance of the surface tension of the wear pads. When the boom decides to move, this pressure drops and the load sense valve dumps all pressure above 230psi back to tank. Gravity is not a friend here. This will repeat itself again and again, causing the shakes.
When the boom is elevated as you point out over 55 degrees there is very little surface tension on the boom and gravity is a good friend.

Let's rule out the surface tension factor first, then we can slice this deeper if we need to.

 

[willie59]

If I'm reading what surfcharlie posted correctly, when the boom if fully raised and extended, it shakes bad when retracting boom. When you drop boom angle down to 55/60 degrees, the shake goes away, right?

Interesting problem, I'm curious to see how this one works out. opcorn

 

[VoodooMojo]

It was usually the pressure relief didn't reach 3000psi that caused the issue.
The counter balance valves rarely caused the problem unless someone had tampered with them. At a 6:1 ratio it only take 500psi pilot to crack the counterbalance open.
A grasshopper can spit 500psi

 

[barklee]

It was usually the pressure relief didn't reach 3000psi that caused the issue.
The counter balance valves rarely caused the problem unless someone had tampered with them. At a 6:1 ratio it only take 500psi pilot to crack the counterbalance open.
A grasshopper can spit 500psi

We had a snorkel doing this.... changed the wear pads, adjusted the cables, etc. It was a piece of crap in the pressure release (i suspect). Changed that and good to go.

 

[Moonlite]

What did you find as the problem?