GM Service Manual Online
For 1990-2009 cars only

Hydraulic Booster Assembly


Object Number: 156501  Size: SH

All M/L models have a hydraulic booster. The hydraulic booster provides power assist using fluid pressure from the power steering pump. The booster assembly is located on the left front cowl. The master cylinder mounts onto the booster assembly.

Hydraulic Booster Assembly


Object Number: 157771  Size: MF
(1)Check Valve Seat
(2)Check Valve Body
(3)Check Valve Relief Spring
(4)Check Valve Washer
(5)Checkball
(6)Body Insert
(7)Plunger
(8)O-ring
(9)Housing Plug
(10)Spool Valve
(11)Spool Valve Checkball
(12)Sleeve Spring
(13)Actuator
(14)External Retainer Ring
(15)Spool Sleeve
(16)Spool Valve Pin
(17)Piston Seal
(18)Piston
(19)Input Lever Pin
(20)Input Lever
(21)Retainer Spring
(22)Relief Valve Spring
(23)Relief Valve Checkball
(24)Relief Valve Seat
(25)Input Rod Ring
(26)Rod and Plunger
(27)Input Rod
(28)Input Rod Bracket
(29)Input Rod Spring
(30)Input Rod End
(31)Input Rod Seals
(32)Housing/Cover Seal
(33)Booster Cover
(34)Output Push Rod Retainer
(35)Piston Return Spring
(36)Output Push Rod
(37)Piston Retainer Spring
(38)Baffle Retainer Spring
(39)Spool Spring
(40)Spool Plug O-ring
(41)Spool Plug
(42)Spool Plug Retaining Ring
(43)Accumulator Retainer Ring
(44)Accumulator
(45)Accumulator Ring
(46)Accumulator Piston
(47)Accumulator Piston O-ring
(48)Accumulator Piston Rings
(49)Retainer Ring
(50)Housing/Cover Bolts
(51)Booster Housing

Power Steering Pump

The power steering pump supplies the hydraulic pressure needed to operate the brake booster. The pump is belt-driven. The pump mount to the engine. The pump provides a continuous fluid flow to the booster, when the engine is running.

Pipes, Hoses, and Fittings

Three flexible hoses route power steering fluid through the hydraulic booster system.

    • One hose supplies pressurized fluid from the power steering pump to the booster.
    • A second hose routes pressurized fluid from the booster to the power steering gear.
    • The third hose routes fluid from the power steering pump to the power steering gear (RWD) or to the power steering cooler pipe (F4WD) mounted under the radiator.

When hoses are removed or replaced, they must be installed to their original positions. Any tie-wraps or insulators that are removed should also be returned to their original positions. Failure to do so may cause damage to the hoses or unwanted noise, vibration, and harshness in the passenger compartment.

Flushing the Hydraulic Booster System

Flushing is required when the fluid in the power steering/hydraulic booster system becomes contaminated. Contaminated fluid in the booster system can cause rubber deterioration. This involves draining the old fluid and replacing it with clean fluid. For the procedure to flush the system, refer to Flushing the Power Steering System in Power Steering Gear and Pump.