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.
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.
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