I’ve searched and found lots of people having the same issue but haven’t found a solution. ‘92 machine. Hydraulics surge about every 3-5 seconds. A few of the hoses get rigid. Few posts have suggested a new accumulator. Has anyone had luck with that solving the problem? Thanks for any input.
Your model and serial number will help with troubleshooting and for determining your hydraulic system and layout.. The first thing you do is have the accumulator pressure checked. If it's in spec then you start hunting the leakage that is causing the machine to cycle and constantly recharge the accumulator. You'll need a 3000 lb. gauge to hook to the quick connects and check pump,accumulator,brakes and all the others. It could be in the ROL system on the back cylinder. Do the functions stop and start operating as it cycles? We need to know any odd thing it's doing as that's helpful in determining issues.
Thanks for the reply Lull 844C-42 Serial# 97W14P22-745 Going to check pressures tomorrow once I look up specs. Is the accumulator something that can be recharged or just replaced? What is ROL? Thanks
On line I thank there are parts and shop manuals available under JLG. Lurk around for them.
It's a 1997 model machine. The accumulator can possibly be resealed and recharged if the bore is good and they can get the ends off. Sometimes they are galled up and won't unscrew. Replacements can be ordered but usually come needing to be charged. A quick test is to take the accumulator off and turn it upside down and take a bent welding rod and push the valve in on the schrader valve and see if oil comes out. If it does the accumulator needs to be rebuilt. The nitrogen charge is about 400-450 lbs so don't get your hands close to the valve. ROL is rear oscillation lock-it locks out the cylinder on the rear axle so it becomes rigid and doesn't pivot when the boom is over 40 degrees-it's to improve stability with the boom raised. Always start with the accumulator first though. Have it checked and let us know how it is and then we can go from there.
Thanks
Appreciate the help. I’ll do some checking.
Heres what I got so far. Put a pressure gauge on the accumulator. Builds to roughly 1600 psi and drops to roughly 1000 within a second or 2. Keeps cycling back and forth. Also the pilot pressure seems slow to build after machine has sat for a while. One thing I found interesting is that the hose for the rear axle lock out cylinder is pressurizing at the same sequence. You think still pull the accumulator and test or look into the ROL system as you had mentioned before?
Always begin with the accumulator. The accumulator balances and cushions the hydraulic system in addition to providing a (storage tank) of pressure to apply the brakes if the engine stops and before the parking brake automatically applies due to loss of pressure. The brakes ROL pilot pressure and other functions are all connected to the accumulator. The fast cycling means there's a big hydraulic pressure leak somewhere and the accumulator is constantly being recharged to compensate for the loss. You are chasing a ghost until you know the state of the accumulator.
Did you ever discover what what was causing your machine to cycle? I have read many post about checking accumulator but never any results. I have a 644b-42 with a similar surge every 45 seconds when cold and about 20-30 seconds after oil is good and warm. My accumulator and other pressures seems to be within spec.
I also would be interested if you found out the issue, I have a 844c that does this too...