GM Lumina/Silhouette/Transport APVs 1990-1999 Repair Guide

ABS Hydraulic Modulator Assembly

Print

The ABS hydraulic modulator/motor pack assembly controls hydraulic pressure to the front and rear calipers or rear wheel cylinders by modulating hydraulic pressure to prevent wheel lock-up. The ABS motor pack consists of three motors, three drive gears, and three Expansion Spring Brakes (ESBs).

REMOVAL AND INSTALLATION




CAUTION
To help avoid personal injury, due to a retained load on the hydraulic modulator, the gear tension relief function of the Tech 1®, or equivalent, scan tool must be performed prior to removal of the ABS hydraulic modulator/master cylinder assembly.

  1. Using a Tech 1® or equivalent scan tool, perform the "Gear Tension Relief Sequence".
  2.  
  3. Unplug the two solenoid electrical connectors.
  4.  
  5. Detach the fluid level sensor electrical connector.
  6.  
  7. Disengage the 6-way ABS motor pack electrical connector.
  8.  
  9. Use a flare nut wrench to disconnect the four brake pipes. Plug the lines to avoid allowing debris to enter and contaminate the system.
  10.  
  11. Unfasten the two nuts attaching the ABS hydraulic modulator/master cylinder assembly to the vacuum booster.
  12.  
  13. Remove the ABS hydraulic modulator/master cylinder assembly from the vehicle.
  14.  

See Figure 1

Click image to see an enlarged view

Fig. Fig. 1: The ABS hydraulic modulator and master cylinder are removed as an assembly

To install:
  1. Install the ABS hydraulic modulator/master cylinder assembly.
  2.  
  3. Install the two nuts attaching ABS hydraulic modulator/master cylinder assembly to vacuum booster. Tighten the nuts to 20 ft. lbs. (27 Nm).
  4.  
  5. Unplug and connect the four brake pipes. Tighten the tube nuts to 18 ft. lbs. (25 Nm).
  6.  
  7. Attach the 6-way ABS motor pack electrical connector.
  8.  
  9. Reconnect the fluid level sensor electrical connector.
  10.  
  11. Attach the two solenoid electrical connectors.
  12.  
  13. Properly bleed the ABS system, as outlined later in this section.
  14.  

 
label.common.footer.alt.autozoneLogo