GM S-Series Pick-ups and SUV's 1994-1999 Repair Guide

Wheel Cylinders

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CAUTION
Brake pads may contain asbestos, which has been determined to be a cancer causing agent. Never clean the brake surfaces with compressed air! Avoid inhaling any dust from any brake surface! When cleaning brake surfaces, use a commercially available brake cleaning fluid.

REMOVAL & INSTALLATION



See Figure 1



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Fig. Fig. 1: Exploded view of the wheel cylinder mounting

A scan tool is absolutely necessary to bleed the brake hydraulic system on models equipped with an Anti-lock Brake System (ABS). If your vehicle is equipped with ABS, be sure to refer to the ABS bleeding procedures in this section before performing any work on your vehicle's brake hydraulic system.

  1. Raise and support the rear of the vehicle safely using jackstands.
  2.  
  3. Remove the tire and wheel assembly.
  4.  
  5. Matchmark and remove the brake drum for access to the wheel cylinder assembly.
  6.  
  7. Remove the brake shoes.
  8.  
  9. Clean away all dirt, crud and foreign material from around wheel cylinder. It is important that dirt be kept away from the brake line when the cylinder is disconnected.
  10.  
  11. Disconnect the inlet tube line from the back of the wheel cylinder. Immediately plug or cap the line to prevent system contamination or excessive fluid loss.
  12.  
  13. Loosen and remove the bolts from the back side of the backing plate, then remove the wheel cylinder assembly.
  14.  

To install:
  1. Place the cylinder into position, then install the retaining bolts and tighten to 115 inch lbs. (13 Nm).
  2.  
  3. Remove the cap or plug, then connect and secure the hydraulic inlet line.
  4.  
  5. Install the brake shoes.
  6.  
  7. Align and install the brake drum, then install the tire and wheel assembly.
  8.  
  9. Bleed the wheel cylinder and adjust the brakes (if necessary).
  10.  
  11. Remove the jackstands and carefully lower the vehicle.
  12.  

OVERHAUL



See Figures 2 through 11

A scan tool is absolutely necessary to bleed the brake hydraulic system on models equipped with an Anti-lock Brake System (ABS). If your vehicle is equipped with ABS, be sure to refer to the ABS bleeding procedures in this section before performing any work on your vehicle's brake hydraulic system.

Wheel cylinder overhaul kits may be available, but often at little or no savings over a reconditioned wheel cylinder. It often makes sense with these components to substitute a new or reconditioned part instead of attempting an overhaul.

If no replacement is available, or you would prefer to overhaul your wheel cylinders, the following procedure may be used. When rebuilding and installing wheel cylinders, avoid getting any contaminants into the system. Always use clean, new, high quality brake fluid. If dirty or improper fluid has been used, it will be necessary to drain the entire system, flush the system with proper brake fluid, replace all rubber components, then refill and bleed the system.

  1. Remove the wheel cylinder from the vehicle and place on a clean workbench.
  2.  
  3. First remove and discard the old rubber boots, then withdraw the pistons. Piston cylinders are equipped with seals and a spring assembly, all located behind the pistons in the cylinder bore.
  4.  



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Fig. Fig. 2: Remove the outer boots from the wheel cylinder

  1. Remove the remaining inner components, seals and spring assembly. Compressed air may be useful in removing these components. If no compressed air is available, be VERY careful not to score the wheel cylinder bore when removing parts from it. Discard all components for which replacements were supplied in the rebuild kit.
  2.  



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Fig. Fig. 3: Compressed air can be used to remove the pistons and seals



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Fig. Fig. 4: Remove the pistons, cup seals and spring from the cylinder

  1. Wash the cylinder and metal parts in denatured alcohol or clean brake fluid.
  2.  



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Fig. Fig. 5: Use brake fluid and a soft brush to clean the pistons ...



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Fig. Fig. 6: ... and the bore of the wheel cylinder


WARNING
Never use a mineral-based solvent such as gasoline, kerosene or paint thinner for cleaning purposes. These solvents will swell rubber components and quickly deteriorate them.

  1. Allow the parts to air dry or use compressed air. Do not use rags for cleaning, since lint will remain in the cylinder bore.
  2.  
  3. Inspect the piston and replace it if it shows scratches.
  4.  



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Fig. Fig. 7: Once cleaned and inspected, the wheel cylinder is ready for assembly

  1. Lubricate the cylinder bore and seals using clean brake fluid.
  2.  
  3. Position the spring assembly.
  4.  
  5. Install the inner seals, then the pistons.
  6.  



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Fig. Fig. 8: Lubricate the cup seals with brake fluid



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Fig. Fig. 9: Install the spring, then the cup seals in the bore



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Fig. Fig. 10: Lightly lubricate the pistons, then install them

  1. Insert the new boots into the counterbores by hand. Do not lubricate the boots.
  2.  



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Fig. Fig. 11: The boots can now be installed over the wheel cylinder ends

  1. Install the wheel cylinder.
  2.  

 
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