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Home >> GMC >> 1980 >> Rally G3500, Van Cargo >> Repair and Diagnosis >> Brakes >> Mechanical - Hydraulic >> Power Brake Units - BENDIX HYDROBOOST >> Hydro-Boost Diagnosis >> Condition >> Accumulator LEAKDOWN - System Does Not Hold Charge >> Preliminary Check

Preliminary Check

Start engine and turn steering wheel until the wheels slightly contact wheel stops. Hold for a maximum of five seconds. Now release steering wheel and turn off engine. Depress and release brake pedal. There should be a minimum of three power assisted brake applications before a hard pedal is obtained.

Re-start engine and turn steering wheel until the wheels lightly contact wheel stops. There should be a light hissing sound as the accumulator is charged. Hold steering wheel lightly against stop for a maximum of five seconds. Release steering wheel and turn off engine. Wait one hour and apply brake pedal (do not re-start engine). There still should be a minimum of three power assisted brake applications before a hard pedal is obtained.

If either of these preliminary checks indicate that the accumulator is not holding a charge, the trouble may be in one of the following causes:

POSSIBLE CAUSE CORRECTION
1) External leakage at accumulator. 1) Replace booster assembly.
2) Internal leakage at accumulator. 2) Replace booster assembly.
3) Internal leakage at booster accumulator valve (if accumulator is not leaking externally or internally). 3) Replace all booster seals and accumulator valves.
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