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Home >> GMC >> 1990 >> Forward Control 6.2 J, Automatic, 400/M40 >> Repair and Diagnosis >> Brakes >> Mechanical - Hydraulic >> DISC & DRUM (C, G, K, P, R & V Series) >> Testing >> Hydro-Boost Testing >> Accumulator Leakdown Test

Accumulator Leakdown Test

  1. Start engine, and charge accumulator by either applying brake with heavy pedal force or turning steering wheel lock-to-lock.
  2. Turn off engine and wait 1 hour. There should be 1 power-assisted brake application with engine off.
  3. If reserve system will not retain a charge for 1 hour, but functions normally immediately following charging; or if accumulator can be heard charging and discharging but will not hold a charge, accumulator valves are at fault. Power piston/accumulator must be replaced.
NOTE: If Hydro-Boost is not functioning, ensure power steering system is operating before replacing Hydro-Boost unit.
Fig 1: Hydro-Boost Fluid Flow Chart
G30363Courtesy of GENERAL MOTORS CORP.