we have a d5c hydrostat series 3. We completed a job loaded and unloaded machine at shop. Tracked about 10 yards from tailer and machine stopped dead in its tracks. Acted like a sylonoid or valve quit working. Checked pumps have 500 psi at idle and 5000 psi at operating rpm. Tried to tow dozer but just slid tracks, pulled axles and was able to tow to shop. Checked final drives no wear, drained oil had normal metal on plug. Oil looked good. Have also checked filters (new). Cat shop sent someone out said it was final drives bring in and they would fix for about 8K. Don't think so. Any suggestions
Sounds to me like your brakes aren't releasing. Safety switch? Sounds like the hydrostats are stroking, right? does it load the engine when you try to move it?
engine is not under a load when engaged
If you are getting 5000 psi, the swashplates in the drive pumps are moving at least some, but lack of engine load says they are not stroking fully. I'm thinking charge pressure is low. Charge releases the brakes and it feeds the pilot joystick for travel. So lack of engine load and brakes stuck on both point to that. Could simply be the charge filter plugged and went on bypass. ....a light is supposed to come on when that happens I thought. Another possibility is the speed sensing valve. It's a valve that has linkage tied into the engine throttle. If the cable fell off in the low idle position, it can keep the pumps from stroking fully. You need a technician who knows the system. It's not the final drives. To suggest left and right side both failed at the exact moment is silly.... run fast from whatever shop told you that. Another possibility: Brake linkage.... if the pedal sticks down, or the linkage is damaged/disconnected, the servo supply is dumped off and the drive pumps will barely stroke. Only the last inch or so of movement actually applies the brakes....