Fault Phenomenon: John Deere 772G grader when driving on muddy ground, pressing the differential lock button, the differential lock does not engage, wheels spin.

Troubleshooting Process:
– Checked cylinder: differential lock cylinder leaking.
– Checked solenoid valve: control solenoid valve stuck.
– Checked gear sleeve: gear sleeve worn or misaligned.
– Checked switch: button switch failed.

Root Cause: The differential lock cylinder seal failed, resulting in insufficient thrust to engage the gear sleeve.

Required Parts: Differential lock cylinder repair kit.