GM Service Manual Online
For 1990-2009 cars only

Preparation Procedure

Trim height is the vehicle ride height. Incorrect trim height can cause bottoming out over bumps. Incorrect trim height can cause damage to the suspension components and symptoms similar to those produced when there is a problem with the wheel alignment. Measure the trim height when diagnosing suspension complaints and before measuring the wheel alignment.

Perform the following steps before measuring the trim height:

  1. Set the tire pressure to the pressure specifications on the tire placard. Refer to Tire Placard .
  2. Verify the tires match the tire size specifications on the tire placard.
  3. Verify the wheels match the wheel size specifications on the tire placard.
  4. Verify the fuel tank is full. Add additional weight in order to simulate a full tank, if necessary.
  5. Verify the rear compartment is empty except for the spare tire and the weight simulating a full fuel tank.
  6. Verify the vehicle is on a level surface, such as an alignment rack.
  7. Close the hood.
  8. Close the doors.
  9. Close the end gate.
  10. Verify the vehicle is not damaged from a collision.

Z Height Dimension Measurement Procedure

The Z height dimension measurement determines the proper ride height for the front of the vehicle.

  1. Use your hands in order to lift the front bumper of the vehicle up approximately 38 mm (1.5 in). Gently remove your hands in order to allow the vehicle to settle.
  2. Use your hands in order to push the front bumper of the vehicle down approximately 38 mm (1.5 in). Gently remove your hands in order to allow the vehicle to settle.
  3. Important: Measure all dimensions vertically.

  4. Measure the Z height dimension on the front lower control arms for the left and the right side of the vehicle.
  5. Measure from the center line of the control arm pivot bolt to the lower edge of the steering knuckle ball joint.

  6. Compare the measurement to the specification. Refer to Trim Height Specifications .
  7. If the measurement is not within 10 mm (0.4 in) of the specification, replace the front springs. Refer to Strut, Strut Component, and Spring Replacement .

D Height Dimension Measurement Procedure

The D height dimension measurement determines the proper ride height for the rear of the vehicle.

  1. Use your hands in order to lift the rear bumper of the vehicle up approximately 38 mm (1.5 in). Gently remove your hands in order to allow the vehicle to settle.
  2. Use your hands in order to push the rear bumper of the vehicle down approximately 38 mm (1.5 in). Gently remove your hands in order to allow the vehicle to settle.
  3. Important: Measure all dimensions vertically.

  4. Measure the D height dimension on the rear suspension for the left and the right side of the vehicle.
  5. If the vehicle has FWD measure from the center line of the rear wheel to the center line of the rear axle pivot bolt.

    If the vehicle has AWD measure from the center line of the rear wheel to the center line of the lower control arm pivot bolt.

  6. Compare the measurement to the specification. Refer to Trim Height Specifications .
  7. If the measurement is not within 10 mm (0.4 in) of the specification, replace the rear springs. Refer to Coil Spring Replacement .