GM Full Size Vans 1987-1997 Repair Guide

Brake Shoes

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INSPECTION



Remove the drum and inspect the lining thickness on both brake shoes. A front brake lining should be replaced if it is less than 1 / 8 in. (3mm) thick at the lowest point on the brake shoe. The wear limit for rear brake linings is 0.030 in. (0.76mm).

Brake shoes should always be replaced in axle sets. The wear specifications given may disagree with your state inspection rules.

REMOVAL & INSTALLATION



With Full Floating Axle

See Figures 1 through 18



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Fig. Fig. 1: Drum Brake Components

  1. Raise and securely support the vehicle using jackstands.
  2.  



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Fig. Fig. 2: Exploded view of the duo-servo drum brake - 1987-92



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Fig. Fig. 3: Exploded view of the duo-servo drum brake - 1993-97

  1. Loosen the parking brake equalizer enough to remove all tension on the brake cable.
  2.  
  3. Remove the brake drums.
  4.  


WARNING
The brake pedal must not be depressed while the drums are removed!

  1. Using a brake tool, remove the shoe return springs. You can do this with ordinary tools, but it isn't easy.
  2.  
  3. Remove the self-adjuster actuator spring.
  4.  
  5. Remove the link from the secondary shoe by pulling it from the anchor pin.
  6.  
  7. Remove the hold-down pins. These are the brackets which run though the backing plate. They can be removed with a pair of pliers. Reach around the rear of the backing plate and hold the back of the pin. Turn the top of the pin retainer 45° with the pliers. This will align the elongated tang with the slot in the retainer. Be careful, as the pin is spring loaded and may fly off when released. Use the same procedure for the other pin assembly.
  8.  
  9. Remove the adjuster actuator assembly.
  10.  

Since the actuator, pivot, and override spring are considered an assembly it is not recommended that they be disassembled.



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Fig. Fig. 4: View of assembled rear drum brake components



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Fig. Fig. 5: Use an evaporative spray brake cleaner to remove brake dust from the components



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Fig. Fig. 6: Use the brake tool to disengage the primary shoe return spring ...



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Fig. Fig. 7: ... then unhook and remove the spring from the shoe



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Fig. Fig. 8: A pair of brake pliers is helpful when separating the secondary return spring from the actuator link



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Fig. Fig. 9: Unhook and remove the spring from the secondary shoe

  1. Remove the shoes from the backing plate. Make sure that you have a secure grip on the assembly as the bottom spring will still exert pressure on the shoes. Slowly let the tops of the shoes come together and the tension will decrease and the adjuster and spring may be removed.
  2.  

If the linings are to be reused, mark them for identification.



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Fig. Fig. 10: Remove the shoe guide from the stud at the top of the backing plate



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Fig. Fig. 11: Remove the actuator link



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Fig. Fig. 12: Use the brake tool to compress the hold-down spring and twist the plate to free the pin



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Fig. Fig. 13: Once the pin and the slot on top of the plate are aligned, separate the hold-down spring and pin



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Fig. Fig. 14: Remove the parking brake strut and spring



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Fig. Fig. 15: Remove the starwheel adjuster screw assembly ...



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Fig. Fig. 16: ... then remove the starwheel adjuster screw spring and primary brake shoe



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Fig. Fig. 17: Remove the parking brake lever from the secondary shoe using a pair of pliers



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Fig. Fig. 18: Remove the secondary shoe from the backing plate

  1. Remove the parking brake lever from the secondary shoe. Using a pair of pliers, pull back on the spring which surrounds the cable. At the same time, remove the cable from the notch in the shoe bracket. Make sure that the spring does not snap back or injury may result.
  2.  

To install:
  1. Use a brake cleaning fluid to remove dirt from the brake drum. Check the drums for scoring and cracks. Have the drums checked for out-of-round and service the drums as necessary.
  2.  
  3. Check the wheel cylinders by carefully pulling the lower edges of the wheel cylinder boots away from the cylinders. If there is excessive leakage, the inside of the cylinder will be moist with fluid. If there is any leakage at all, a cylinder overhaul is in order. DO NOT delay, as a brake failure could result.
  4.  

A small amount of fluid will be present to act as a lubricant for the wheel cylinder pistons.

  1. Check the flange plate, which is located around the axle, for leakage of differential lubricant. This condition cannot be overlooked as the lubricant will be absorbed into the brake linings and brake failure will result. Replace the seals as necessary.
  2.  

If new linings are being installed, check them against the old units for length and type.

  1. Check the new linings for imperfections.
  2.  


WARNING
It is important to keep your hands free of dirt and grease when handling the brake shoes. Foreign matter will be absorbed into the linings and result in unpredictable braking.

  1. Lightly lubricate the parking brake and cable and the end of the parking brake lever where it enters the shoe. Use high temperature, waterproof, grease or special brake lube.
  2.  
  3. Install the parking brake lever into the secondary shoe with the attaching bolt, spring washer, lockwasher, and nut. It is important that the lever move freely before the shoe is attached. Move the assembly and check for proper action.
  4.  
  5. Lubricate the adjusting screw and make sure that it works freely. Sometimes the adjusting screw will not move due to lack of lubricant or dirt contamination and the brakes will not adjust. In this case, the adjuster should be disassembled, thoroughly cleaned, and lubricated before installation.
  6.  
  7. Connect the brake shoe spring to the bottom portion of both shoes. Make certain that the brake linings are installed in the correct manner, the primary and secondary shoe in the correct position. If you are not sure remove the other brake drum and check it.
  8.  
  9. Install the adjusting mechanism below the spring and separate the top of the shoes.
  10.  
  11. Make the following checks before installation:
    1. Be certain that the right hand thread adjusting screw is on the left hand side of the vehicle and the left hand screw is on the right hand side of the vehicle.
    2.  
    3. Make sure that the star adjuster is aligned with the adjusting hole.
    4.  
    5. The adjuster should be installed with the starwheel nearest the secondary shoe and the tension spring away from the adjusting mechanism;
    6.  
    7. If the original linings are being reused, put them back in their original locations.
    8.  

  12.  
  13. Install the parking brake cable.
  14.  
  15. Position the primary shoe (the shoe with the short lining) first. Secure it with the hold-down pin and with its spring by pushing the pin through the back of the backing plate and, while holding it with one hand, install the spring and the retainer using a pair of needlenose pliers. Install the adjuster actuator assembly.
  16.  
  17. Install the parking brake strut and the strut spring by pulling back the spring with pliers and engaging the end of the cable onto the brake strut and then releasing the spring.
  18.  
  19. Place the small metal guide plate over the anchor pin and position the self-adjuster wire cable eye.
  20.  


WARNING
The wire should not be positioned with the conventional brake installation tool or damage will result. It should be positioned on the actuator assembly first and then placed over the anchor pin stud by hand with the adjuster assembly in full downward position.

  1. Install the actuator return spring. DO NOT pry the actuator lever to install the return spring. Position it using the end of a screwdriver or another suitable tool.
  2.  

If the return springs are bent or in any way distorted, they should be replaced.

  1. Using the brake installation tool, place the brake return springs in position. Install the primary spring first over the anchor pin and then place the spring from the secondary show over the wire link end.
  2.  
  3. Pull the brake shoes away from the backing plate and apply a thin coat of high temperature, waterproof, grease or special brake lube in the brake shoe contact points.
  4.  


WARNING
Only a small amount of lubricant is necessary. Be sure to keep it away from the brake linings.

See Figure 19



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Fig. Fig. 19: Using the proper tool, install the brake shoe return springs:

  1. Once the complete assembly has been installed, check the operation of the self-adjusting mechanism by moving the actuating lever by hand.
  2.  
  3. Adjust the brakes.
    1. Turn the star adjuster until the drum slides over the brakes shoes with only a slight drag. Remove the drum:
    2.  
    3. Turn the adjuster back 1 1 / 4 turns.
    4.  
    5. Install the drum and wheel and lower the vehicle.
    6.  
    7. If the adjusting hole in the drum has been punched out, make certain that the insert has been removed from the inside of the drum. Install a rubber hole cover to keep dirt out of the brake assembly. Also, be sure that the drums are installed in the same position as they were when removed, with the locating tang in line with the locating hole in the axle shaft flange.
    8.  
    9. Make the final adjustment by backing the vehicle and pumping the brakes until the self-adjusting mechanisms adjust to the proper level and the brake pedal reaches satisfactory height.
    10.  

  4.  
  5. Adjust the parking brake. Refer to the procedure in this section.
  6.  


WARNING
Avoid overtightening the lug nuts to prevent damage to the brake drum. Alloy wheels can also be cracked by overtightening. Use of a torque wrench is highly recommended.

With Semi-Floating Axle

See Figures 20, 21 and 22

  1. Jack up and securely support the vehicle using jackstands.
  2.  
  3. Loosen the parking brake equalizer enough to remove all tension on the brake cable.
  4.  



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Fig. Fig. 20: Exploded view of the leading/trailing drum brake



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Fig. Fig. 21: Push the parking brake lever off its stop



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Fig. Fig. 22: Removing the adjuster actuator

  1. Remove the brake drums. If difficulty is till encountered, remove the access hole plug in the backing plate and insert a metal rod to push the parking brake lever off its stop.
  2.  

The brake pedal must not be depressed while the drums are removed!

  1. Raise the lever arm of the actuator until the upper end is clear of the slot in the adjuster screw. Slide the actuator off the adjuster pin.
  2.  
  3. Disconnect the actuator from the brake shoe.
  4.  
  5. Remove the hold-down pins. These are the brackets which run though the backing plate. They can be removed with a pair of pliers. Reach around the rear of the backing plate and hold the back of the pin. Turn the top of the pin retainer 45° with the pliers. This will align the elongated tang with the slot in the retainer. Be careful, as the pin is spring loaded and may fly off when released. Use the same procedure for the other pin assembly.
  6.  
  7. Pull the lower ends of the shoes apart and lift the lower return spring over the anchor plate. Remove the spring from the shoes.
  8.  
  9. Lift the shoes and upper return spring along with the adjusting screw, from the backing plate. Some spreading of the shoes is necessary to clear the wheel cylinder and axle flange. Remove the upper spring.
  10.  
  11. Remove the retaining ring, pin, spring washer and parking brake lever.
  12.  

If the linings are to be reused, mark them for identification.

To install:
  1. Use a brake cleaning fluid to remove dirt from the brake drum. Check the drums for scoring and cracks. Have the drums checked for out-of-round and service the drums as necessary.
  2.  
  3. Check the wheel cylinders by carefully pulling the lower edges of the wheel cylinder boots away from the cylinders. If there is excessive leakage, the inside of the cylinder will be moist with fluid. If there is any leakage at all, a cylinder overhaul is in order. DO NOT delay, as a brake failure could result.
  4.  

A small amount of fluid will be present to act as a lubricant for the wheel cylinder pistons.

  1. Check the flange plate, which is located around the axle, for leakage of differential lubricant. This condition cannot be overlooked as the lubricant will be absorbed into the brake linings and brake failure will result. Replace the seals as necessary.
  2.  

If new linings are being installed, check them against the old units for length and type.

  1. Check the new linings for imperfections.
  2.  


WARNING
It is important to keep your hands free of dirt and grease when handling the brake shoes. Foreign matter will be absorbed into the linings and result in unpredictable braking.

  1. Install the parking brake lever assembly The concave side of the washer should be against the shoe.
  2.  
  3. Install the adjuster pin in the shoe so that the pin projects 0.268-0.276 in. (6.8-7.0mm) from the side of the shoe where the actuator is installed.
  4.  
  5. Apply an approved brake lubricant grease to the threads of the adjuster screw, socket and socket face.
  6.  
  7. Make certain that the brake linings are positioned correctly and connect the upper spring. If you are not sure of which shoe goes where, remove the other brake drum and check it. Don't over-stretch the spring; you'll ruin it. The spring can't be stretched, safely, more than 8.04 in. (204mm).
  8.  
  9. Install the adjusting mechanism between the shoes. Make the following checks before installation:
    1. Be certain that the adjusting screw assembly engages the adjuster shoe and parking brake lever.
    2.  
    3. Make sure that the spring clip is positioned towards the backing plate.
    4.  
    5. The linings are in the correct positions. The shoe with the parking brake lever is the rear shoe.
    6.  

  10.  
  11. Coat the shoe mounting pads on the backing plate with a thin coat of lithium grease.
  12.  
  13. Position the assembly on the backing plate, engaging the upper shoe ends with the wheel cylinder pushrods.
  14.  
  15. Hook the lower return spring into the shoe ends and spread the shoes, guiding the lower spring over the anchor plate. Don't over-stretch the spring; you'll ruin it. The spring can't be stretched, safely, more than 4 1 / 4 in. (108mm).
  16.  
  17. Install the hold-down spring assemblies.
  18.  
  19. Place the adjuster actuator over the end of the adjusting pin so its top leg engages the notch in the adjuster screw.
  20.  
  21. Install the actuator spring. Make sure that the free end of the actuator engage the notch of the adjuster nut. Don't over-stretch the spring. Its maximum stretch is 3 1 / 4 in. (83mm).
  22.  
  23. Connect the parking brake cable to the lever. Adjust the parking brake:
    1. Measure the brake drum inside diameter.
    2.  
    3. Turn the adjuster nut until the brake shoe maximum diameter is 0.01-0.02 in. (0.25-50mm) less than the brake drum diameter.
    4.  
    5. Make sure that the stops on the parking brake levers are against the edge of the brake shoe web. If the cable is holding the stops off the edge, loosen the adjustment.
    6.  
    7. Tighten the cable at the adjuster nut until the lever stops begin to move off the shoe webs.
    8.  
    9. Loosen the adjustment nut until the lever stops are just touching the shoe webs. There should be no more than 0.5mm clearance between the stops and the webs.
    10.  

  24.  
  25. Install the drums and wheels.
  26.  
  27. Pump the brake pedal 30-35 times with normal force. Pause about 1 second between each stroke.
  28.  
  29. Depress the parking brake pedal 6 clicks. The wheels should be locked.
  30.  
  31. Release the parking brake. The wheels should rotate freely.
  32.  

 
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