GM Astro/Safari 1985-1996 Repair Guide

Brake Disc (Rotor)

Print

The 2-wheel drive brake disc rotor and the wheel bearing hub assembly are designed as one piece; therefore, to remove the brake disc, remove the wheel bearing assembly.

The 4-wheel drive brake disc rotor is separate from the hub assembly and can be removed without removing the hub and bearings assembly. The hub and bearing assembly is non-serviceable and has to be replaced as a unit.

REMOVAL & INSTALLATION



2WD Model

See Figure 1



Click image to see an enlarged view

Fig. Fig. 1: Exploded view of brake assembly-Two wheel drive

  1. Raise and support the front of the vehicle safely using jackstands.
  2.  
  3. Remove the tire and wheel assembly.
  4.  
  5. Remove the brake caliper mounting bolts and carefully remove the caliper (along with the brake pads) from the rotor. Do not disconnect the brake line; instead wire the caliper out of the way with the line still connected.
  6.  

Once the rotor is removed from the vehicle the wheel bearings may be cleaned and repacked or the bearings and races may be replaced. For more information, please refer to the wheel bearing procedures in General Information & Maintenance of this guide.

  1. Carefully pry out the grease cap, then remove the cotter pin, spindle nut, and washer. Remove the hub, being careful not to drop the outer wheel bearings. As the hub is pulled forward, the outer wheel bearings will often fall forward and they may easily be removed at this time.
  2.  

To install:
  1. Carefully install the wheel hub over the spindle.
  2.  
  3. Using your hands, firmly press the outer bearing into the hub.
  4.  
  5. Loosely install the spindle washer and nut, but do not install the cotter pin or dust cap at this time.
  6.  
  7. Install the brake caliper.
  8.  
  9. Install the tire and wheel assembly.
  10.  
  11. Properly adjust the wheel bearings:
    1. Spin the wheel forward by hand and tighten the nut to 12 ft. lbs. (16 Nm) in order to fully seat the bearings and remove any burrs from the threads.
    2.  
    3. Back off the nut until it is just loose, then finger-tighten the nut.
    4.  
    5. Loosen the nut 1 / 4 - 1 / 2 turn until either hole in the spindle lines up with a slot in the nut, then install a new cotter pin. This may appear to be too loose, but it is the correct adjustment.
    6.  
    7. Proper adjustment creates 0.001-0.005 in. (0.025-0.127mm) end-play.
    8.  

  12.  
  13. Install the dust cap.
  14.  
  15. Install the wheel/hub cover, then remove the supports and carefully lower the vehicle.
  16.  

4WD Model

See Figure 2



Click image to see an enlarged view

Fig. Fig. 2: Rotor, hub and bearing assembly-All wheel drive

  1. Raise and support the front of the truck safely using jackstands under the frame.
  2.  
  3. Remove the tire and wheel assembly.
  4.  
  5. Remove the brake caliper mounting bolts and carefully remove the caliper (along with the brake pads) from the rotor. Do not disconnect the brake line; instead wire the caliper out of the way with the line still connected.
  6.  
  7. If equipped, remove the lockwashers from the hub studs in order to free the rotor.
  8.  
  9. Remove the brake disc (rotor) from the wheel hub.
  10.  

To install:
  1. Inspect the disc for nicks, scores and/or damage, then replace if necessary.
  2.  
  3. Install the disc over the wheel hub studs.
  4.  
  5. If used, install the lockwashers over the studs.
  6.  
  7. Install the brake caliper and pads. For details, please refer to the caliper procedure located earlier in this section.
  8.  
  9. Install the tire and wheel assembly.
  10.  
  11. Remove the jackstands and carefully lower the vehicle. DO NOT attempt to move the vehicle unless a firm brake pedal is felt.
  12.  

INSPECTION



See Figure 3



Click image to see an enlarged view

Fig. Fig. 3: Use a dial indicator to determine brake disc runout

  1. Raise and support the front of the vehicle on jackstands. Remove the wheels.
  2.  
  3. To check the disc runout, perform the following procedures:
    1. Using a dial indicator, secure and position it so that the button contacts the disc about 1 in. (25mm) from the outer edge.
    2.  
    3. Rotate the disc. The lateral reading should not exceed 0.004 in. (0.1mm). If the reading is excessive, recondition or replace the disc.
    4.  

  4.  
  5. To check the disc parallelism, perform the following procedures:
    1. Using a micrometer, check the disc thickness at 4 locations around the disc, at the same distance from the edge.
    2.  
    3. The thickness should not vary more than 0.0005 in. (0.013mm). If the readings are excessive, recondition or replace the disc.
    4.  

  6.  
  7. The surface finish must be relatively smooth to avoid pulling and erratic performance, also, to extend the lining life. Light rotor surface scoring of up to 0.015 in. (0.38mm) in depth, can be tolerated. If the scoring depths are excessive, refinish or replace the rotor.
  8.  

 
label.common.footer.alt.autozoneLogo