Doosan DX300LC Service Manual — Wiring Diagrams

Follow the manual's own triage order on page 282 — hydraulic flow first, pressure second — then check reservoir oil level and test main relief pressure; spec is 330 kg/cm2 in normal operation and 350 kg/cm2 with "Pressure Up" (page 72). The "Troubleshooting – Hydraulic Problems" table on pages 297-298 traces sluggish performance across all functions back to a worn main pump, a mis-set main relief valve or low oil, and lists a clogged oil cooler, loose fan belt and a relief valve in constant use among the causes of abnormally high oil temperature. Both the return line and the pilot circuit carry 10 micron full-flow filters (page 276).

Check the bearing on the schedule the manual sets — at least twice a year (page 170). For axial play, push the attachment against the ground to lift the excavator and read a dial indicator at four points 90° apart around the bearing, recording every reading. For lateral play, fully retract the arm and bucket cylinders, extend the bucket tip forward and push it sideways; less than 100 lb of force should be needed to take up the clearance. The manual gives no single wear number here — the criterion is the trend, and play approaching twice the as-new measurement means the bearing is near the end of its service life.

Measure track link pitch; the standard is 216 mm (8.504 in) per page 237, where bushing outside diameter starts at 66.5 mm and becomes a replace item at 59 mm. Check lower roller tread diameter against the 178 mm (7.008 in) standard on page 238 — 166 mm is the recommended maintenance limit and 164 mm the repair limit. Re-tension afterwards through the grease fitting in the middle of each side frame, with the machine jacked up per page 233; never back the grease cylinder valve off more than one full turn.

Test the parking brake first: it releases at 9 kg/cm2 (128 psi) per page 408, and a dragging brake mimics a weak motor. Check drain pressure against the same specification table — 2 kg/cm2 normal, 10 kg/cm2 surge. The troubleshooting table on page 298 lists a dragging travel brake, poorly adjusted track tension, low oil in idlers or rollers and a twisted track frame among the causes of slow travel, and a damaged center joint as a cause of a dead travel motor. Verify travel reduction gear oil is filled to the 7.0 litre capacity shown on page 476.

Remove the center joint and inspect the O-rings and slipper seals — the manual says they cannot be reused and must be replaced. Measure the spindle-to-body clearance; replace or repair either component if wear exceeds 0.1 mm (0.0039 in) per page 322, and replace anything showing more than 0.5 mm of visible wear between shaft, shim and spacer. On reassembly, wrap the PT 1/4 plug 6-10 times with teflon tape and torque it to 3-4 kg•m (page 323), and engage the M12 cover bolt at 10-12.5 kg•m (page 324).