JLG 1998 450A Manlift Drive Motor Issues

[davis1676]

I have a 1998 JLG 450A Ford motor/carb. Lift has a M46 Sundstrand drive pump ( I now have 3 M46 pumps, dont ask why?) I have a problem with forward and reverse on the machine. I have blanked off port A on pump with test gauge and also port B and moved manual EDC lever back and forth and gauge on port A and port B will jump up to around 5000 psi and load engine to the point it will almost die . I can move manual lever on EDC with the hoses reattached and in one direction drive pump loads up and tries to turn wheels put cant because the brakes are not releasing. I move the EDC lever in the other direction pump will not load up or will not try to turn wheels.

My question is how to test drive motors. I read on forum to open drain lines on motors and check the flow of return. I am thinking that I am loosing charge pressure in one or both of the drive motors (2WD). I opened one drain port on one drive motor and in the neutral position I had a steady flow coming out and when I engaged the EDC lever it really sprayed out. I didnt know what I was doing so I stopped and put it back together and came home reading over the hydraulic schematic. Do I check flow in the neutral position appx 2 gallons a minute or should that be engaged at appx 2 gpm?

I have released brakes by moving brake hose on the combination block from port B to another port so they release as soon as the machine is cranked. I am pretty certain the only reason they dont release normally is the charge pressure drop when engaging drive motors.

From my understanding of the schematic the only place I could loose charge pressure since I blanked off port A and port B of the drive pump and it operated correctly, would be the drive motors internally or a open axle lockout or problem with the combination/divider block.

What should I check next?
I do not have any external leaks either.
every drive pump I have installed has acted the same way as the one thats on the machine now.
I kept thinking it was in the pump or EDC because the machine sometimes will move forward fair and reverse not very good ( very weak).
when oil is cold it moved better but as oil warmed up hardly no movement either direction not even if you move manual lever on EDC.

 

[willie59]

From my understanding of the schematic the only place I could loose charge pressure since I blanked off port A and port B of the drive pump and it operated correctly, would be the drive motors internally or a open axle lockout or problem with the combination/divider block.

Your forgetting about the center rotating joint. Disconnect the two main drive hoses at the flow divider valve and dead head the hose into a pressure gauge like you did at port A and B at the pump, see if you get the 5000 psi at those hoses.

 

[davis1676]

ok and thanks for a quick reply. I will do it in the morning.

 

[Hardline]

Wait, on a 450A? Correct me if I'm wrong as its been 8 years since I have worked on those booms. But didn't the 450A Not have a rotate coupler? Don't they just have a live fitting that allows them to just go 350* to the stop? Problem may be in the flow divider combiner itself though.

 

[willie59]

Hmm, good question Hardline, it's been so long since I've worked on one that I can't recall for certain myself. :tong

 

[davis1676]

no rotating coupler. I replaced all the cartridges in the flow divider last year but going to check it tomorrow anyways. just dont know what kind of flow i should be getting out of the returns on the drive motors.

 

[Hardline]

The first thing I would do is pull the cartridges on the flow divider for blown orings. You can cap the hoses at each motor one at a time and make it pull against the brake at that wheel. That will isolate each motor. If one lugs the motor and the other doesn't you know the motor that does not lug the engine is the failure. Freewheel that hub and machine will probably drive on one wheel with the other lines capped off if you need to move it out of the way.

 

[davis1676]

ok got out this morning and pulled the flow divider box and found the problem. Someone had routed charge pressure to unlabeled port. That port was suppose to have a check valve assembly cartridge in it and they installed the cartridge assembly in another port and screwed the wrong cap on it and smashed it down in that port. I had a extra cartridge and got it charge pressure routed to the right port. So we are rolling again. thanks for all the help.

 

[Hardline]

Wow, gotta love when people go playing around with stuff they should not be playing with. Glad you got it figured out. JJ

 

[lantraxco]

It's a miracle they didn't damage the manifold block!

 

[willie59]

It's a miracle they didn't damage the manifold block!

Agreed, and like Hardline said, obviously someone who has no business with a wrench in his hand. And that's one of those things none of us would have guessed, just no way to see that coming.

 

[davis1676]

Well its hats off to the helpful people on this forum that convinced me to take another look at the distribution block.