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Dan, Technician
Category: Construction and Road Equipment
Satisfied Customers: 5284
Experience:  17+ yrs. shop and field experience with all major brands of heavy equipment and trucks - 1995 WyoTech graduate.
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I have a Komatsu D39PX-21 dozer. It barely moves going

Customer Question

I have a Komatsu D39PX-21 dozer. It barely moves going forward, but goes really fast in reverse. Any ideas on what the problem may be and what I need to check?
Submitted: 1 year ago.
Category: Construction and Road Equipment
Expert:  Dan replied 1 year ago.

Hi my name is***** is your serial number? Check the filter for fine metal debris to eliminate the possibility of a pump or component problem occurring. Let me know

Customer: replied 1 year ago.
Serial number is *****
Customer: replied 1 year ago.
It seems like if that was the problem the dozer wouldn't move in any direction. Any other suggestions?
Expert:  Dan replied 1 year ago.

That is not true actually. This machine is hydrostatic drive and travel is controlled by the pumps and drive motors. The pump controls signal the direction of travel and speed. click below

Travel circuit

Expert:  Dan replied 1 year ago.

what did you find in the hydrostatic filter and the oil from it? Was it like fine glitter?

Expert:  Dan replied 1 year ago.

This is part of the troubleshooting process. I worked for Komatsu, Volvo, Cat, and Deere before going independent.

Expert:  Dan replied 1 year ago.

Here is your PPC (pilot pressure control) block with solenoid valves that your control pressure comes from for your functions. You could have a problem with one of the valves with debris or sticking not signalling the pumps for full flow forward or a problem in the pump control itself not stroking to full flow in forward.

PPC diagram

Expert:  Dan replied 1 year ago.

Cut open you PPC charge filter and inspect for metal/debris using a filter cutting tool to prevent contaminating your sample.

charge filter

Expert:  Dan replied 1 year ago.

doubt it but also make sure the tow valve is not in the tow position.... Very unlikely when travel is only affected in forward.

Tow valve

Expert:  Dan replied 1 year ago.

Here are your pumps, Hydrostatic and charge


Expert:  Dan replied 1 year ago.

This is the main return filter back to tank. any internal problems in the main pressure circuit will pick up the contamination on the way back to the tank. Sample this filter as well.

Return filter

Expert:  Dan replied 1 year ago.

Are you getting any warning or errors from the controller or faults on the display? the next step is to get test gauges and confirm your charge pressure and main pressures, etc

Customer: replied 1 year ago.
Thanks, ***** ***** got it figured out. There was something binding and we have to replace a lever.
Expert:  Dan replied 1 year ago.

Thanks for the update. Must be referring to the linkage inside the console under the controls. Glad you found it.

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