81307256084 Clutch booster

Pneumatic clutch servo for MAN heavy trucks with manual or TipMatic AMT gearboxes. The clutch assemblies used in heavy commercial vehicles generate clamp forces that would be physically impractical for the driver to overcome through pedal effort alone — this servo unit resolves that by using compressed air from the vehicle's braking circuit to amplify the hydraulic force from the master cylinder, generating the full release load at the pressure plate. Progressive failure develops over weeks or months as internal seals harden and leak: the driver first notices that the pedal becomes heavier, then that full gear engagement at standstill becomes difficult, and finally that the clutch will not release completely even at full pedal travel. Sudden failure — typically from a cracked diaphragm — presents as an immediately dead-weight pedal with no assistance. Before condemning the servo, check the air supply pressure at the servo inlet and inspect the one-way check valve that prevents brake circuit depressurisation into the clutch circuit — air starvation produces identical symptoms to a failed servo. Bleed the clutch hydraulic circuit after any servo replacement.