Fault Phenomenon: Caterpillar 950 wheel loader when engaging forward or reverse gear, the machine moves weakly or cannot move at all.

Troubleshooting Process:
– Checked transmission fluid: low fluid level or deteriorated quality.
– Checked torque converter: stator one-way clutch slipping.
– Checked transmission control valve: shift control valve spool stuck or spring broken.
– Checked friction discs: transmission clutch friction discs severely worn.

Root Cause: The pressure reducing valve spool in the transmission control valve is stuck, causing insufficient oil pressure to the clutch, preventing the friction discs from clamping.

Required Parts: Clean or replace transmission control valve assembly, replace transmission fluid and filter.