D31PX-21 Stucked in left reverse, won't start and when finally did, is not SAFE !

[Richard V]

SN is 500127. First I don't know much about dozers. I bought this machine about 2 months ago. It has 12,000 hours. The engine was easy to start (even in cold weather) and was running fine. We've put about 10 hours since I bought it and we were pushing mud and wood debris (no rocks). Everything was fine until last week until it started not going straight. Eventually going reverse it would go from right to left by itself, applying brakes did not stop it nor bringing down the left handle (safety) to disable traction, the dozer kept going reverse and with only the left track working. The only way to stop this was to turn the keyswitch to OFF. We tried restarting the engine and no luck. It turns a couple of times then appears like the batteries are dying and turning very slow. Tried recharging the batteries, still no luck does not start. So...someone more knowledgeable, than me, came by and suggested to disable the brake system by unplugging a hose and applying oil pressure to it to release the brakes. Surprisingly this enabled the machine to start (less load on the engine) but then the dozer started going backward with only the left track running. So, neutral position on the joystick = dozer going reverse with left track running, joystick in back position activates reverse right track and then dozer goes somewhat straight in reverse. joystick in forward position make right track forward by left track still goes reverse. The person tells me the problem is with the pump controlling the left motor. Any ideas ?