JLG 450a has no drive power

[bigboytoy]

I am borrowing a friends 2001 jlg450 with 2900hrs on it. from my experience with these lifts I notice it has no drive power on soft ground. I am only sinking maybe an 3/4 of an inch into sod, no mud, no wheel spin. when the boom is lowered it kicks it up into high gear and idle like it should but it just moves normal...I have used these machines and a good machine will just about throw you out of the basket it jumps so much. the second clue is I am trimming a tree on level ground but soft so I realize it will only creep but instead it won't move. Other functions like lift and extend, travel at normal speeds...my guess is rebuild hydraulic drive motors? any advice for my friends JLG 450....till I get the tree trimmed I think I will trip the boom switch because it is so tame.

 

[willie59]

Could be the drive controller circuit card is faulty or simply out of adjustment.

 

[bigboytoy]

thanks for the reply

 

[davis1676]

i have the same machine and I am still pulling my hair out with it. I have had the hydraulic pump overhauled and got it to move forward and backwards but only when the motor kicks up. High idle in soft ground like you describe wont move. You can check the drive by using the manual switch on the backside of the drive pump that should tell you whether it is in the controller or not because using the switch by hand bypassing the control voltage from the platform just switch your ignition key to ground control and move the small plastic switch back and forth but make sure you are not where you will get run over.

 

[Jim913]

Will a small hose leak somewhere in the system not obvious cause this condition? Mine goes fast on level or down grade but just started acting like it won’t go up a small grade. It goes at first and slowly gets slower until it stops. If I let off the forward drive, idle a few seconds and go again it will mover normally several feet and them slow down again. Repeat that process 100x and got it to shed and noticed the platform level hose was dripping.

 

[Jim913]

And what would soft ground have to do with this condition? I don’t understand how the machine would know the ground is soft and or why that would change how the machine responds

 

[bigboytoy]

something is by passing the oil pressure ... ?? ... I would check that theory with tests ... maybe one drive motor is letting it bypass .. jack it up ..? I am no expert good luck

 

[JLGRI]

check your grounds in the basket control box. See if you have +volts on any of the ground wires when the machine is in the run position (pull red button out but no engine running) if you see any voltage on the ground check your ground wire conenction in the lower control box. i believe they are the first 5 wires in the upper left. I have seen the 3rd wire be completely charred. a bad ground will wreck havoc.