GM Lumina/Silhouette/Transport APVs 1990-1999 Repair Guide

Shock Absorbers

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TESTING



The purpose of the shock absorber is simply to limit the motion of the spring during compression and rebound cycles. If the vehicle is not equipped with these motion dampers, the up and down motion would multiply until the vehicle was alternately trying to leap off the ground and to pound itself into the pavement.

Contrary to popular rumor, the shocks do not affect the ride height of the vehicle. This is controlled by other suspension components such as springs and tires. Worn shock absorbers can affect handling; if the front of the vehicle is rising or falling excessively, the "footprint" of the tires changes on the pavement and steering is affected.

One of the simplest tests of shock absorbers is to simply push down on one corner of an unladen vehicle and release it. Observe the motion of the body as it is released. In most cases, it will come up beyond it original rest position, dip back below it and settle quickly to rest. This shows that the damper is controlling the spring action. Any tendency to excessive pitch (up-and-down) motion or failure to return to rest within 2-3 cycles is a sign of poor function within the shock absorber. Oil-filled shocks may have a light film of oil around the seal, resulting from normal breathing and air exchange. This should NOT be taken as a sign of failure, but any sign of thick or running oil definitely indicates failure. Gas filled shocks may also show some film at the shaft; if the gas has leaked out, the shock will have almost no resistance to motion.

See Figure 1

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Fig. Fig. 1: When fluid is seeping out of the shock absorber, it's time to replace it

While each shock absorber can be replaced individually, it is recommended that they be changed as a pair (both front or both rear) to maintain equal response on both sides of the vehicle. Chances are quite good that if one has failed, its mate is weak also.

REMOVAL AND INSTALLATION



  1. Open the lift gate, remove the trim cover and remove the upper shock attaching nut.
  2.  

See Figures 2 through 6

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Fig. Fig. 2: The trim cover is held in place by snaps and can be removed by carefully lifting it off



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Fig. Fig. 3: The cover can be completely removed to get it out of the way



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Fig. Fig. 4: There is a rubber bumper cover over the top mount of the shock



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Fig. Fig. 5: Pull the rubber cover off for access to the shock upper retaining nut



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Fig. Fig. 6: Use a deep socket with an extension to remove the shock upper mounting nut

  1. Support the rear axle and safely raise the vehicle.
  2.  

See Figure 7

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Fig. Fig. 7: This is the top of the shock as viewed inside the wheel housing

  1. If equipped with electronic level control, disconnect the air hose.
  2.  
  3. Remove the lower attaching bolt and nut and remove the shock.
  4.  

See Figures 8 through 13

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Fig. Fig. 8: The bottom mount of the shock is secured with a nut and bolt



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Fig. Fig. 9: Using a socket and ratchet to loosen the bottom mounting bolt



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Fig. Fig. 10: Remove the shock from the bottom mount ...



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Fig. Fig. 11: ... then lower the shock and remove it from the vehicle. Removing the upper mounting brace with the shock, to inspect for wear



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Fig. Fig. 12: Standard rear shock absorber, with attaching parts



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Fig. Fig. 13: Exploded view of the shock absorber attachment

To install:
  1. Position the shock at the lower attachment, feed the bolt through the holes, and loosely install the nut,
  2.  
  3. If equipped with electronic level control, connect the air hose.
  4.  
  5. Lower the vehicle enough to guide the upper stud through the body opening and install the nut loosely.
  6.  
  7. Tighten the lower nut to 44 ft. lbs. (59 Nm).
  8.  
  9. Lower the vehicle the rest of the way, then tighten the upper nut to 16 ft. lbs. (22 Nm).
  10.  
  11. Install the rubber bumper and trim cover.
  12.  

 
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