GM Service Manual Online
For 1990-2009 cars only

Removal Procedure

Caution: The modulator drive gears are under spring load and will turn during disassembly. After removing brake modulator drive gear cover, exercise extreme care not to place fingers into the gear set, since fingers can be pinched by rotating gears.

Notice: Do not allow gear to turn while removing the retaining nut, since the modulator piston can hit the top of the modulator bore, damaging the piston. Place a screwdriver through the holes in the gears (not between the gears) into the recessed hole in the modulator base. This will prevent the gear from turning, aiding in gear removal.

Important: Do not repair damaged motor-pack assemblies or brake modulators. Besides modulator drive gears replacement, repair of the motor-pack assembly and of the brake modulator assemblies is not authorized. Do not oil or lubricate the gears on the motor-pack assembly.


    Object Number: 221843  Size: MH
  1. Remove the hydraulic modulator assembly. Refer to Brake Pressure Modulator Valve Assembly Replacement .
  2. Remove the 6 screws (5) that attach the gear cover (4).
  3. Remove the gear cover (4) from the motor-pack assembly (1).
  4. Remove the 4 screws (6) that connect the motor-pack assembly to the modulator.
  5. Important: Use care when handling the motor-pack assembly. Replace the motor-pack assembly if the motor-pack assembly is dropped or damaged during handling.

  6. Separate the motor-pack assembly (1) from the hydraulic modulator (2).

  7. Object Number: 165947  Size: SH

    Notice: Do not allow gear to turn while removing the retaining nut, since the modulator piston can hit the top of the modulator bore, damaging the piston. Place a screwdriver through the holes in the gears (not between the gears) into the recessed hole in the modulator base. This will prevent the gear from turning, aiding in gear removal.

  8. Remove the 3 retaining nuts of the modulator drive gear.
  9. Remove the gears from the modulator.

Installation Procedure

Important: Use care when handling the motor-pack assembly. Replace the motor-pack assembly if the motor-pack assembly is dropped or damaged during handling.


    Object Number: 165947  Size: SH
  1. Position the modulator drive gears (3) onto the modulator drive shaft.
  2. Notice: Use the correct fastener in the correct location. Replacement fasteners must be the correct part number for that application. Fasteners requiring replacement or fasteners requiring the use of thread locking compound or sealant are identified in the service procedure. Do not use paints, lubricants, or corrosion inhibitors on fasteners or fastener joint surfaces unless specified. These coatings affect fastener torque and joint clamping force and may damage the fastener. Use the correct tightening sequence and specifications when installing fasteners in order to avoid damage to parts and systems.

  3. Install the three gear retaining nuts.
  4. Tighten
    Tighten the nuts to 8.5 N·m (76 lb in).


    Object Number: 165951  Size: SH
  5. With either of the modulators positioned upside down, and the gears facing you, rotate each ABS brake modulator gear counterclockwise until movement stops.
  6. Rotating the modulator gears will cause the following conditions:

    • The pistons on the ABS brake modulator will be positioned very close to the top of the modulator bore.
    • The brake bleeding procedure is simplified.

    Object Number: 221843  Size: MH
  7. Position the motor-pack assembly (1) onto the modulator (2), aligning the 3 motor-pack assembly gears with the modulator gears (3).
  8. Install the 4 screws (6) that connect the motor-pack assembly to the modulator .
  9. Tighten
    Tighten the 4 screws (6) to 5 N·m (44 lb in).

  10. Install the gear cover (4) onto the modulator (2) with the six Torx® head screws (5).
  11. Tighten
    Tighten the 6 screws (5) to 4 N·m (36 lb in).

  12. Install the Hydraulic Modulator assembly into the vehicle. Refer to Brake Pressure Modulator Valve Assembly Replacement .
  13. Perform the Motor Rehome Procedure.
  14. Perform the Diagnostic System Check - ABS .