The ABS brake modulator/brake motor pack assembly controls the hydraulic pressure to the front calipers and rear calipers (or rear wheel cylinders, as equipped) by modulating the hydraulic pressure to reduce the tendency of wheel lock-up.
The basic ABS brake modulator configuration consists of gear subassemblies, ball screws, nuts, pistons and hydraulic check valves. The ABS brake motor pack consists of three motors, three drive gears and three Expansion Spring Brakes (ESBs). The ESBs are used to hold the pistons in the upmost (or home) position. An ESB is a spring that is retained in a housing at a close tolerance. One end of the spring is in contact with the motor drive dog and the other end is in contact with the pinion drive dog. In normal braking, brake pressure is present on the top of the piston, applying a downward force. The force applies a counterclockwise torque to the motor pinion which tries to rotate the spring counterclockwise. The counterclockwise torque expands the spring outward within the housing and prevent gear rotation
Removal & Installation
- Using a Tech 1® or equivalent scan tool, perform the Gear Tension Relief Sequence.
- Disconnect the negative battery cable.
- Detach the two brake solenoid valve electrical connectors.
- Detach the brake fluid level indicator sensor electrical connector.
- Detach the ABS brake motor pack 6-way electrical connector.
- Using a brake line wrench, disconnect the four brake lines. Cap the disconnected lines to prevent the loss of fluid and the entry of moisture and contaminants.
- Remove the two nuts holding the ABS brake modulator/master cylinder assembly to the vacuum booster and remove the assembly from the vehicle.
- Installation is the reverse of the removal process. Torque the nuts holding the ABS brake modulator/master cylinder assembly to the vacuum booster to 20 ft. lbs. (27 Nm) and the brake line tube nuts to 18 ft. lbs. (24 Nm). Verify that all electrical connectors are secure.
- Properly bleed the system, as outlined later in this section.
- Connect the negative battery cable.