Case 850K Won't move

[Coy Lancaster]

CAL POT is for the throttle and should be calibrated first

 

[Dickie7802]

Hey Gary I need some help with a case 750K that I cannot get the brake potentiometer to adjust

 

[Dickie7802]

I bought a case 750K with 700 original hours. Dozer is strong and pushes good. The only thing I can find that don’t work is the brake pedal. The park brake on the left when engaged stops the machine dead in its tracks. The one on the right seems to have no effect as long as the one on the left is not engaged. I checked the 521 wire and four 3.74 volts but the voltage doesn’t vary with the pedal. It reads the same no matter where the pedal is in the stroke. I had a hard code of 4331 out of range and when trying to calibrate I got err range. I thought the potentiometer looked new but hard to say. I could see where the connector on the machine side wires had been pierced to probe them so someone been monkeying with it. I replaced the potentiometer and same result. Tried to calibrate and same message. I started to check by the manual and found two of the wires to the potentiometer plug on the machine side were crossed by checking continuity to x50 at the pcm. I swapped the wires and checked it a few more times and the continuity checks were as the manual says they should be. I now have no code but I cannot get the brake switch to calibrate. It says cal fail. I back probed the decel potentiometer and found voltage varies on the return wire with movement of the pedal. Even when the brake switch is not mounted but plugged in it will not vary the voltage when turned. Always reads the same. I’m wondering if the new potentiometer has croaked due to someone crossing the pcm wires of maybe the pcm is shot. Any help would be greatly appreciated. Not sure whether to buy another 150 dollar sensor or try a pcm. I have a 5 volt reference at the brake switch but I think the pcm grounds that switch. Anyone know anything about this?

 

[CJsegan]

View attachment 182019


The potentiometer connectors should be a 3 pin deutsch if I remember correctly. Letters for the pin locations are sometimes on the connector. The wire numbers are not likely not visible. Just use a small cotter pin or paper clip to back probe the connector when checking voltages.

I don't believe your throttle potentiometer is your issue, but you may have to adjust it anyways in order to complete the calibration.

Gary, is this for the Reverse ratio switch? the 4 position knob to the left of the joystick I am having an issue with mine I get zero ohm reading and my 850K series 2 will not move forward or reverse, and I have no display I'm heading out to check all fuses any advise on making it move or display fuse location?