GM Full-Size Trucks 1988-1998 Repair Information

Component Replacement

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See Figures 1, 2, 3 and 4



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Fig. Fig. 1: Component locations



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Fig. Fig. 2: Data link connector-anti-lock brake system



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Fig. Fig. 3: Front wheel speed sensor-2WD models



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Fig. Fig. 4: Front wheel speed sensor-4WD models

REMOVAL & INSTALLATION



Electro-Hydraulic Control Unit (EHCU) Valve

The EHCU valve is not serviceable and must never be disassembled or repaired. If tests indicate the unit is faulty, the EHCU must be replaced.

  1. Label and unplug the electrical connectors from the EHCU.
  2.  
  3. Label and disconnect the brake lines from the EHCU.
  4.  
  5. Remove the bolts holding the EHCU bracket to the vehicle. Remove the bracket and hydraulic unit as an assembly.
  6.  
  7. Once removed from the vehicle, separate the bracket from the EHCU.
  8.  

To install:
  1. Assemble the EHCU to its bracket and install the bolts. Tighten the bolts to 5 ft. lbs. (7 Nm). Overtightening these bolts can cause excessive noise during system operation.
  2.  
  3. Install the assembly into the vehicle. Tighten the mounting bolts to 33 ft. lbs. (45 Nm).
  4.  
  5. Connect the brake lines in their original locations. Tighten the fittings to 16 ft. lbs. (25 Nm).
  6.  
  7. Connect the electrical connectors. Make certain each is squarely seated and secure.
  8.  
  9. Bleed the EHCU valve, then bleed the entire brake system.
  10.  

Bleeding the EHCU

Bleeding the EHCU requires the use of the TECH-1 scanner or its equivalent and the appropriate cartridge. Additionally, 3 tools, J-39177 or equivalent, are required. Bleeding cannot be performed without this equipment.

The EHCU must be bled after replacement or if air is trapped within the unit. It must be bled after bleeding the master cylinder and before bleeding the individual wheel circuits.

The Internal Bleed Valves on either side of the unit must be opened 1 / 4 - 1 / 2 turn before bleeding begins. These valves open internal passages within the unit. Actual bleeding is performed at the two bleeders on the front of the EHCU module. The bleeders must not be opened when the system is not pressurized. The ignition switch must be OFF or false trouble codes may be set.

  1. Open the internal bleed valve 1 / 4 - 1 / 2 turn each.
  2.  
  3. Install one tool J-39177 on the left bleed stem of the EHCU. Install one tool on the right bleed stem and install the third tool on the combination valve.
  4.  
  5. Inspect the fluid level in the master cylinder, filling if needed.
  6.  
  7. Slowly depress the brake pedal and hold it down.
  8.  
  9. Open the left bleeder on the front of the unit. Allow fluid to flow until no air is seen or until the brake pedal bottoms.
  10.  
  11. Close the left bleeder, then slowly release the pedal. Wait 15 seconds.
  12.  
  13. Repeat Steps 4, 5 and 6, including the 15 second wait, until no air is seen in the fluid.
  14.  
  15. Tighten the left internal bleed valve to 5 ft. lbs. (7 Nm).
  16.  
  17. Repeat Steps 3-7 at the right bleeder on the front of the unit.
  18.  
  19. When bleeding of the right port is complete, tighten the right internal bleed valve to 5 ft. lbs. (7 Nm).
  20.  
  21. Remove the 3 special tools.
  22.  
  23. Check the master cylinder fluid level, refilling as necessary.
  24.  
  25. Bleed the individual brake circuits at each wheel.
  26.  
  27. Switch the ignition ON . Use the hand scanner to perform 3 function tests on the system.
  28.  
  29. Carefully test drive the vehicle at moderate speeds; check for proper pedal feel and brake operation. If any problem is noted in feel or function, repeat the entire bleeding procedure.
  30.  

Front Wheel Speed Sensors
Two-wheel drive models (Except 1995-98)
  1. Elevate and safely support the vehicle.
  2.  
  3. Remove the wheel.
  4.  
  5. Remove the brake caliper.
  6.  
  7. Remove the hub and rotor assembly.
  8.  
  9. Unplug the sensor wire connector.
  10.  
  11. Disconnect the sensor wire from the clip(s) on the upper control arm.
  12.  
  13. Remove the bolts holding the splash shield.
  14.  
  15. Remove the splash shield and sensor assembly.
  16.  
  17. Remove the gasket.
  18.  

To install:
  1. Install a new gasket.
  2.  
  3. Mount the sensor and splash shield to the knuckle. Install the retaining bolts and tighten them to 89 inch lbs. (10 Nm).
  4.  
  5. Connect the wiring to the clips on the upper control arm. Check the wiring for correct routing.
  6.  
  7. Connect the wiring connector.
  8.  
  9. Install the hub and rotor assembly.
  10.  
  11. Install the brake caliper.
  12.  
  13. Install the wheel. Lower the vehicle to the ground.
  14.  

Four-wheel drive models (Except 1995-98)
  1. Elevate and safely support the vehicle.
  2.  
  3. Remove the wheel.
  4.  
  5. Disconnect the sensor electrical connector.
  6.  
  7. Release the sensor wire from the clip(s) on the upper control arm.
  8.  
  9. Remove the bolts holding the sensor; remove the sensor from its mount.
  10.  
  11. Reassemble in reverse order. Tighten the sensor mounting bolts to 11 ft. lbs. (15 Nm).
  12.  

Two-wheel drive 1995-98 models (except C3HD)
  1. Elevate and safely support the vehicle.
  2.  
  3. Remove the wheel.
  4.  
  5. Remove the brake caliper.
  6.  
  7. Remove the hub and rotor assembly.
  8.  
  9. Unplug the sensor wire connector.
  10.  
  11. Use a 3 / 16 inch drill to remove the sensor harness clip rivets.
  12.  
  13. Disconnect the clips from the sensor wire. Save the clips for the new sensor.
  14.  
  15. Remove the sensor assembly bolts and nut.
  16.  
  17. Remove the bolts holding the splash shield.
  18.  
  19. Remove the splash shield and sensor.
  20.  
  21. Remove the gasket.
  22.  

To install:
  1. Install a new gasket.
  2.  
  3. Mount the sensor and splash shield to the knuckle. Install the retaining bolts and tighten the splash shield mounting bolts to 12 ft. lbs. (16 Nm). Tighten the sensor retainers to 19 ft. lbs. (26 Nm).
  4.  
  5. Install the harness clips in their original position and attach them using 3 / 16 inch rivets.
  6.  
  7. Attach the sensor wiring connector.
  8.  
  9. Install the hub and rotor assembly.
  10.  
  11. Install the brake caliper.
  12.  
  13. Install the wheel. Lower the vehicle to the ground.
  14.  

Four-wheel drive 1995-98 models (except C3HD)
  1. Elevate and safely support the vehicle.
  2.  
  3. Remove the wheel.
  4.  
  5. Remove the brake caliper.
  6.  
  7. Remove the rotor assembly.
  8.  
  9. Disconnect the sensor wiring harness from the clip on the control arm and the clip on the frame.
  10.  

The sensor mount in a bore that leads to the center of the sealed bearing. Be careful when cleaning and working around the bore. Make sure no dirt or contaminates enters the bore or it may damage the bearing.

  1. Clean the area around the sensor thoroughly.
  2.  
  3. Unfasten the sensor retainer.
  4.  
  5. Remove the sensor by pulling it straight out. Do not use a prytool to remove the sensor as it could break the sensor off in the bore.
  6.  
  7. Make sure to remove the sensor O-ring and discard it.
  8.  

To install:
  1. Lubricate the new sensor O-ring with wheel bearing grease, install the O-ring on the sensor and lubricate the area just above and below the O-ring on the sensor body with wheel bearing grease.
  2.  
  3. Install the sensor assembly in the bore and tighten its retaining bolt to 13 ft. lbs. (18 Nm).
  4.  
  5. Attach the sensor electrical connection.
  6.  
  7. Route the sensor wiring harness in its original location and attach it with new mounting clips.
  8.  
  9. Install the rotor and caliper.
  10.  
  11. Install the wheel and lower the vehicle.
  12.  

1995 C3HD models
  1. Elevate and safely support the vehicle.
  2.  
  3. Remove the wheel.
  4.  
  5. Remove the brake caliper.
  6.  
  7. Remove the hub and rotor assembly.
  8.  
  9. Unplug the sensor electrical connection.
  10.  
  11. Unfasten the sensor bracket retainers.
  12.  
  13. Unfasten the sensor retainers and remove the sensor from the knuckle.
  14.  
  15. Installation is the reverse of removal.
  16.  

1996-98 C3HD models
  1. Elevate and safely support the vehicle.
  2.  
  3. Remove the wheel.
  4.  
  5. Remove the brake caliper.
  6.  
  7. Remove the hub and rotor assembly.
  8.  
  9. Remove the splash shield.
  10.  
  11. Disconnect the sensor wire mounting clip attached to the upper king pin cap and the mounting clip attached to the frame rail.
  12.  
  13. Unplug the sensor electrical connection.
  14.  
  15. Unfasten the sensor to bracket retainers. It is not necessary to remove the bracket unless it is damaged.
  16.  
  17. Remove the speed sensor.
  18.  

To install:

The speed sensor on these models is adjustable by using the slots in the mounting bracket. The sensor must be properly adjusted to obtain the correct air gap.

  1. Install the sensor on the bracket and finger-tighten its retainers.
  2.  
  3. Place the hub and rotor assembly on a surface with the tone wheel facing up making sure not to damage the studs.
  4.  
  5. Mark the position of the rotor relative to the hub so the rotor can be reinstalled in the same position.
  6.  
  7. Unfasthe the bolts attaching the rotor to the hub and separate the rotor from the hub.
  8.  
  9. Install the hub and tone wheel assembly onto the spindle.
  10.  
  11. Install the outer bearing, washer and spindle nut. Tighten the spindle nut to 12 ft. lbs. (16 Nm) while rotating the hub in either direction. Do not back off the nut.
  12.  
  13. Insert a flexible shim stock or equivalent between the tone wheel and the sensor. The shim stock must be 0.050 inch (1.25mm) thick and the length and width of the shim stock must be enough to cover the face of the sensor. If shim stock is nit available, regular notebook or writing paper can be used as long as the specification for thickness, length and width are strictly adhered to.
  14.  
  15. Press the sensor firmly against the shim stock and tone wheel.
  16.  
  17. Tighten the retainers as follows:
    1. Left-hand lower attaching nut: 10 ft. lbs. (14 Nm).
    2.  
    3. Left-hand upper attaching nut: 10 ft. lbs. (14 Nm).
    4.  
    5. Right-hand upper attaching nut: 10 ft. lbs. (14 Nm).
    6.  
    7. Right-hand lower attaching nut: 10 ft. lbs. (14 Nm).
    8.  

  18.  
  19. Remove the shim stock and make sure the sensor does not contact the tone while when rotated.
  20.  
  21. Install the splash shield making sure to route wire through the opening in the shield. Tighten the splash shield bolts to 13 ft. lbs. (17 Nm).
  22.  
  23. Route the wiring harness to its original location and attach the mounting clips.
  24.  
  25. Install the rotor making sure to line up the reference marks made previously. Tighten the bolts to 175 ft. lbs. (237 Nm).
  26.  
  27. Install the caliper and the wheel. Lower the vehicle.
  28.  

Rear Wheel Speed Sensor
EXCEPT SUBURBAN
  1. Elevate and safely support the vehicle.
  2.  
  3. Remove the wheel.
  4.  
  5. Remove the brake drum.
  6.  
  7. Remove the primary brake shoe.
  8.  
  9. Disconnect the sensor wiring at the connector.
  10.  
  11. Remove the sensor wire from the rear axle clips.
  12.  
  13. Remove the 2 bolts holding the sensor.
  14.  
  15. Remove the sensor by tracking the wire through the hole in the backing plate.
  16.  

To install:
  1. Route the wire through the hole in the backing plate and fit the sensor into position.
  2.  
  3. Install the 2 bolts; tighten them to 26 ft. lbs. (35 Nm).
  4.  
  5. Secure the sensor wire within the rear axle clips.
  6.  
  7. Connect the sensor wiring to the harness connector.
  8.  
  9. Install the primary brake shoe.
  10.  
  11. Install the brake drum.
  12.  
  13. Install the wheel. Lower the vehicle to the ground.
  14.  

SUBURBAN WITH 4L60E

Speed sensor removal/installation tool J-38417 or its equivalent is required for this procedure.

  1. Elevate and safely support the vehicle. The speed sensor is located on the left side of the transmission.
  2.  
  3. Disconnect the sensor wiring connector.
  4.  
  5. Remove the retaining bolt holding the sensor.
  6.  
  7. Using the removal tool, remove the sensor from the transmission case. Have a pan available to catch fluid spillage.
  8.  

To install:
  1. Coat the O-ring on the sensor with a thin coat of transmission fluid.
  2.  
  3. Using the installation tool, install the sensor into the case. Tighten the mounting bolt to 8 ft. lbs. (11 Nm).
  4.  
  5. Connect the sensor to the wiring harness.
  6.  
  7. Lower the vehicle to the ground. Check the transmission fluid level and fill to the correct level if necessary.
  8.  

SUBURBAN WITH 4L80E AND MANUAL TRANSMISSION
  1. Elevate and safely support the vehicle. The speed sensor is located on the left side of the transmission.
  2.  
  3. Disconnect the sensor wiring connector.
  4.  
  5. Remove the retaining bolt holding the sensor.
  6.  
  7. Remove the sensor from the transmission case. Have a pan available to catch fluid spillage.
  8.  

To install:
  1. Coat the O-ring on the sensor with a thin coat of transmission fluid.
  2.  
  3. Install the sensor into the case. Tighten the mounting bolt to 5 ft. lbs. (7 Nm).
  4.  
  5. Connect the sensor to the wiring harness.
  6.  
  7. Lower the vehicle to the ground. Check the transmission fluid level and fill to the correct level if necessary.
  8.  

 
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