GM S10/S15/Sonoma Pick-Ups 1982-1993 Repair Manual

Brake Disc (Rotor)

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INSPECTION



See Figure 1



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Fig. Fig. 1: Check rotor lateral run-out using a dial indicator

Check the disc brake rotor for scoring, cracks or other damage. Rotor run-out should be measured while the rotor is installed, while rotor thickness/thickness variation may be checked with the rotor installed or removed. Use a dial gauge to check rotor run-out. Check the rotor thickness to make sure it is greater than minimum thickness and check for thickness variations using a caliper micrometer.

  1. Raise and support the front of the vehicle safely using jackstands.
  2.  
  3. Remove the front wheels.
  4.  
  5. Visually inspect the rotor for cracks, excessive scoring or other damage. A light scoring of the surface which does not exceed 0.06 in. (1.5mm) in depth is normal and should not be considered detrimental to brake operation.
  6.  

Before attempting to check rotor run-out on 2wd vehicles, make sure the wheel bearings are properly adjusted. On all vehicles, the bearings must be in good condition and not contain excessive play.

  1. Check the disc for excessive run-out using a dial indicator:
    1. Position and secure a dial indicator so that the button contacts the disc about 1 in. (25.4mm) from the outer edge. Set the dial indicator to zero.
    2.  
    3. Rotate the disc one complete revolution. The lateral run-out reading should not exceed 0.004 in. (0.1mm) on vehicles through 1992 or 0.003 in. (0.08mm) for 1993 vehicles. If the reading is excessive, recondition or replace the disc.
    4.  

  2.  
  3. Check the disc minimum thickness and the disc parallelism (thickness variation):
    1. Use a micrometer to check the disc thickness at 4 locations around the disc. Make sure the measuring point is at the same distance from the edge at all locations.
    2.  
    3. The thickness should be greater than the minimum specification (which is normally cast onto the disc) and should not vary more than 0.0005 in. (0.013mm). If the variations are excessive, recondition or replace the disc. A disc which is smaller than the discard dimension MUST be replaced for safety.
    4.  

  4.  

REMOVAL & INSTALLATION



2WD Model
  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 inSection 1 of this manual.

  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 Figures 2, 3 and 4

  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, refer to please 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.  



Click image to see an enlarged view

Fig. Fig. 2: The brake disc is easily removed once the tire and wheel is out of the way



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Fig. Fig. 3: If equipped, remove the lockwashers from the hub studs



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Fig. Fig. 4: Remove the rotor by pulling it of the hub studs

 
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