GM Full Size Vans 1987-1997 Repair Guide

Rear Wheel Speed Sensors

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On early model vehicles, the rear wheel speed sensors are held by 2 bolts at each rear wheel. The brake drum and primary brake shoe must be removed for access.

Late models vehicles receive the rear wheel speed signal from the Vehicle Speed Sensor (VSS) buffer. The VSS is located at the left rear of the transmission. The buffer, a unit for interpreting the electrical signal from the sensor, is located behind the instrument cluster. The buffer, formerly known as the Digital Ratio Adapter Controller (DRAC), is matched to the final drive and tire size of each vehicle. If the final drive or tire size is changed, the buffer unit must be replaced to maintain accurate speedometer/odometer readings and proper ABS function.

TESTING



See Figure 1



Click image to see an enlarged view

Fig. Fig. 1: Rear wheel speed sensor resistance chart

  1. Disconnect the negative battery cable.
  2.  
  3. Raise the vehicle and support with jackstands. Remove the wheel and tire assembly.
  4.  
  5. Disconnect the rear wheel speed sensor.
  6.  
  7. Measure the resistance of the sensor and compare to the chart.
  8.  
  9. Replace the sensor if the resistance does not meet specification.
  10.  

REMOVAL & INSTALLATION



Early Model Vehicles

See Figure 2



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Fig. Fig. 2: The tone ring splines need to be clean to work properly

  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 retainer(s) 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 retainer(s); 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.  

Late Model Vehicles
WITH 4L60E TRANSMISSION

See Figures 3, 4, 5, 6 and 7



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Fig. Fig. 3: Vehicle speed sensor mounting



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Fig. Fig. 4: Unplug the weatherpak connector from the VSS



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Fig. Fig. 5: The VSS is held by the one bolt and clamp



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Fig. Fig. 6: Withdraw the VSS from the transmission



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Fig. Fig. 7: Fluid will come out of the VSS opening so be ready to catch the spillage

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.  

WITH W4L80E TRANSMISSION
  1. Elevate and safely support the vehicle. Both speed sensors are located on the left side of the transmission.
  2.  
  3. Disconnect the sensor wiring connector(s).
  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(s) 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.  

WITH 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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