I have a 2001 JLG 2646 E2 electric scissor lift serial 0200094173. Has 211 hours of run time total so it is really in good shape. It has brand new batteries (2 days old). It lifts up and down perfect with plenty of power, the steering moves perfect, the brake cylinder retracts fine. However,when you try to drive forward or backward it hesitates. Usually it hesitates for 5 to 10 seconds before it then moves. The pump motor is whining away as normal, but it just does not move. When it does finally move it usually gives a slight jerk and then rolls on. If it has been run in the drive mode for awhile and then you stop it for a few seconds, it seems to drive on again with a significantly lesser amount of hesitation (maybe 1-2 seconds). However, if you let it sit and do not drive it for about 3-5 minutes then it again hesitates in moving for 5 to 10 seconds. Sometimes longer. The pump motor whines but the lift does not roll forward. Almost like it is "slipping" but then suddenly grabs after this long period of time. Sometimes it never grabs and slips until you turn it off, but mostly it grabs after 5-10 seconds. At first, I found that it would drive forward or reverse right off if I pressed the right turn or left turn button at the same time. However, this then stopped helping and that trick no longer works. I have been at a loss to what is wrong here. Here is what I have done so far: 1) I checked the solenoids on the drive forward and drive reverse. Voltage was about 20 V. This seemed to be a little low as I thought it might be 24V but the solenoids worked well and had correct resistance. I thne bought brand new batteries but still no improvement. 2) I then bypassed the solenoid control by disconnecting the wiring and hardwiring a separate 24V source to energize the solenoids. This way I took the joystick/controller out of the picture. Same symptoms. Hesitated driving. 3) I then removed the entire forward/reverse solenoid spool valve (Rexroth ManneMann valve 4WE6E60) and brought it to my clean bench where I took it apart. I checked to make sure that the spool moved OK when the solenoids were energized. The spool moved back and forth fine. (I did notice that the spool diameter and the bore of the housing had about .002 clearance and there were no O rings on it. I am not an expert on spool valves so maybe this is fine, but I would have thought it would have been a tighter clearance. However, there was not signs of wear or galling on the spool OD or bore ID so maybe this is how it is supposed to be?) Everything fine in the spool, no gunk, perfectly clean. 4) I put the entire thing back together and remounted on the JLG lift. When I tried it, same thing. Lift hesitated just like before. 5) I then checked the TOW valve to make sure it was closed. It is tight. If you unscrew it the lift does not drive at all which is how it should be. I am not sure if there is any leakage or this TOW valve is a problem but from what I can tell it seems fine. I took the valve out and inspected it and it looked brand new and seemed to seat fine. 6) I checked the drive in both high and low speed. The lift does the same thing (hesitates) in both the slow and high speed settings. 7) I have just got a gauge to measure the pressure from the MP port. Will do this tomorrow. However, since everything else works fine and strong, I don't think this is an issue with the pressure. 8) I thought about the drive motors themselves having problems. However when it does move it moves strong. Also, the machine only has 211 hours on it. I would not think the motors (or both motors at the same time) would be bad but I have not disproved this yet. 9) Has plenty of fluid, filter is brand new, no clogs in air vent, hoses are fine. 10) I am not sure when this drive hesitation started as we had been using it mostly for up/down. I did move the machine recently with my Lull and it got shook around slightly but nothing drastic. Any suggestions would be greatly appreciated. I have all the JLG on line manuals but they do very little to help with this particular problem. I had tried calling JLG but they would not talk to me as I do not have an account. I tried to get an account only to find that I would need to be a dealer and sell a certain number of machines to qualify. (I am a builder and not a JLG sales store) I tried calling JLG service but no one can get to me for quite a long time and when they do, travel time and costs get pretty prohibitive unless I was to ship the machine to them. I do not have a trailer or truck big enough to move this machine. I would really like to be able to fix this on my own as I enjoy working on these machines. Thanks for any suggestions!
you can do a case drain test on the drive motors to verify motor leakage. also there is a cushion cylinder in the drive circuit. You can cap the cylinder off temporarily to see if it is bypassing. the oil is going somewhere...either back to tank through a valve, an actuator, or slipping by internally in the pump.
VoodooMojo: Thanks for the feedback. I worked on the lift all day and finally solved it. It now works fine. It was not very straightforward but here is what I did: 1) I put a pressure gauge on the MP port and it read 1600 psi. 2) I capped off the cushion cylinder as you said and checked the MP port pressure. Was now 3200 psi! I tried driving the lift and it seemed to drive fine. Thus, it seemed that the cushion cylinder must have been blowing by. 3) I put everything back together, had some lunch and then went to drive the lift back out to the work zone. HOWEVER, it now did NOT drive!! 4) I put the pressure gauge on the MP port and then it read 1200 psi? I know it just read 3200 about 20 minutes before??? 5) I then thought maybe it was the pump? Maybe it cooled off and now leaked? I put gauge right on pump and it read 4000 psi. Thus, the pump was good! 6) I then though maybe it was the main relief valve. I took this apart and inspected and it looked fine. I put back together and now I got 2000 psi from MP port? Why was this different yet again? Was it leaking out through the drive motors? 7) I then took off every single output hose to the drive motors, the steering, the lift, etc and capped off. Everything was now capped. All 11 outputs. I put ran the pump again and now 1500 psi? How could this be? 8) Something very strange and random was happening. I then took out every other fitting from the valve block. All relief valves, all flow dividers, shuttle valves, stem valves, etc. It was now a complete basket case and neatly spread over the entire floor. 9) I then inspected every last part until I finally found the issue. 10) There was a big metal chip about .200 in x .180 x .005" thick lightly wedged in the end of one of the valve orfices. It was not jammed so it must have just floated into that particular spot. It appeared to be a piece of aluminum, probably a machining chip from the big aluminum main valve block. I bet it was never cleaned out entirely when this valve block was originally made at the factory and somehow it just broke off and started floating around. Maybe this machining chip or burr was held in place internally inside the main housing and when I shook the lift around a bit from carrying it in my Lull, this chip broke loose? 11) What must have been happening is that this chip began floating around and randomly wedged itself in each of the other valves. This caused the random behavior. When it wedged in the flow diverter or relief it caused random blow by. 12) In addition, the cushion cylinder was bad, which made the debugging even more difficult as there were really two problems going on at once. I removed the chip, cleaned out everything, put the hoses all back in place, and now the MP pressure was 3200! It now ran perfect! I then, as a test, put the cushion cylinder back in place. Bad idea. Pressure dropped back to 1500 psi. I recapped it and then 3200 psi! Thus the cushion cylinder was indeed also bad making it a compound problem. I then tried out my "New" lift and it worked prefect. I have driven it all around, back forward, up down, steer left, right. No problems. Other than the jerky start, stop from capping the cushion cylinder, it is fine. Will now order a new cushion cylinder. Hope this helps someone else with a seemingly impossible problem like this. TT
Wow I'm impressed you performed more tests and work than most aerial lift mechanics I've know or been around. Kudos for figuring it out and not being a parts changer. I know on a lot of scissor lifts I've been around the cushion cylinders were known for getting beat inside and contaminating the system with aluminum shavings. Not saying that's where your metal came from but I'd check it out.