Fault Phenomenon: Komatsu HD785 mining truck when engaging the exhaust brake, there is no braking effect, and abnormal noise comes from the exhaust pipe.

Troubleshooting Process:
– Checked butterfly valve: connection between valve plate and shaft broken.
– Checked bearings: valve shaft bearings seized, causing torsional break.
– Checked cylinder: drive cylinder actuates normally but valve does not move.
– Checked carbon buildup: severe carbon buildup causing valve sticking.

Root Cause: The exhaust brake butterfly valve shaft broke due to fatigue from long-term high-temperature corrosion and excessive torque caused by carbon buildup sticking.

Required Parts: Replace exhaust brake butterfly valve assembly.