GM Buick/Oldsmobile/Pontiac/Full-Size 1975-1990 Repair Guide

Hydraulic (Hydro-boost®) Power Booster



See Figure 1

Power steering fluid and brake fluid cannot be mixed; also, power steering fluid damages seals designed for brake fluid, and brake fluid damages power steering type seals.

  1. With the engine off, pump the brake pedal 5 times to deplete fluid stored in the accumulator.
  3. Remove the two master cylinder mounting nuts and pull the master cylinder forward and away from the power booster with brake lines attached.
  5. Disconnect the three hydraulic lines at the booster. Remove the retainer and washer at the brake pedal, inside the vehicle.
  7. Remove the four nuts attaching the booster to the firewall from inside the vehicle and remove it. Remove the gasket.

To install:
  1. Position the booster on the dash panel over the gasket and install the four mounting nuts onto the firewall from inside the vehicle. Torque to 15 ft. lbs. (20 Nm). Install the pedal rod washer and retainer.
  3. Position the master cylinder to the hydro-booster, install the mounting nuts, and torque to 20 ft. lbs. (27 Nm).
  5. Install the three hydraulic lines, torquing the two high pressure lines (which are screwed in) to 20 ft. lbs. (27 Nm).
  7. Install power steering fluid into the steering pump until fluid is at the base of the pump reservoir neck.
  9. Disconnect the diesel injection pump 12V wire or the 12V wire to the distributor. THE ENGINE MUST NOT START.
  11. Crank the engine for several seconds. Then, check the fluid level and replenish as necessary.
  13. Connect wiring and start the engine. Turn the wheel from stop to stop two full times. Then, turn the engine off and depress the brake pedal five times to fully discharge the hydraulic accumulator. Check and if necessary replenish the hydraulic fluid.
  15. Again start the engine and turn the wheel from lock to lock two full times. If there is visible foam in the power steering pump reservoir, wait an hour for it to dissipate (engine off). Then, replenish fluid.

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Fig. Fig. 1: Hydro-boost power booster mounting