New Holland DC70, DC80, DC100 Crawler Dozer Service Manual (incl. Wiring)

Check the hydrostatic transmission troubleshooting chart. Test boost pressure at engine idle; it should read 20 bar (290 PSI) and climb to 33 bar (478 PSI) at max engine speed on page 122. If pressure is low or absent, pull the drive motor and inspect the rotor distributor assembly for scoring or wear, this is the most common cause of total propulsion loss and usually means the rotating group needs replacement.

Drain a sample of hydrostatic fluid and check for contamination or metal fines before doing anything else. Refer to the troubleshooting procedures to isolate whether the fault is pump-side or motor-side. If flow is inconsistent, run the hydraulic pump flow test described and compare output against a known-good side; a worn pump or motor bearing will show up as flow that falls off under load.

Shut down and let the system cool, then check the cooling circuit for debris packed against the heat exchanger fins. Pump coupler oil temperature is rated to a max of 105° C (221° F) on page 134, and gearbox oil should not exceed 90-95° C (194-203° F) intermittently per page 186. If temps climb past these limits repeatedly, clean the cooler core and verify fan blades are not cracked or loaded with debris before returning to service.

Verify boost pressure first using the commissioning checks; low boost pressure starves the drive motor and mimics a traction problem. Also inspect the undercarriage for elongated pin holes or worn bushings per the major malfunction list on page 204, since stretched track chain robs pulling force just as easily as a hydraulic fault does.

Check track tension against the adjustment procedure on page 214 first; a chain running too loose or too tight accelerates wear on pins and bushings. When reinstalling a master link on a DC80, torque it to 250 Nm (180 ft-lb) with lubrication per page 206; DC70 units call for 150 Nm (110 ft-lb) on page 205. Under-torquing the master link is a common reason it walks loose again within a few hours of operation.

Inspect the revolution sensor mounting for a bent bracket or debris in the gap first. Set the mechanical air gap to 0.5 mm (0.19 in) per the adjustment spec on page 309, then check the electrical output voltage matches spec at that gap. If readings still drift, run the electronic control unit self-learning reset covered on page 302 to relearn the throttle lever position.