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Home >> Chevrolet >> 1990 >> Step Van 7.4 N, Standard >> Repair and Diagnosis >> External Pages >> Different car >> Section 14 (Drive Axle - 7.5", 7.625", 8.5" & 9.5") >> Overhaul >> Reassembly & Adjustments >> Drive Pinion Depth & Bearing Preload

Drive Pinion Depth & Bearing Preload

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  1. Drive pinion rear bearing shim thickness must be determined whenever a new axle housing, ring and pinion set, or pinion bearings are installed. Shim pack thickness is determined by using Pinion Setting Gauge Set (J-21777).
  2. If removed, install pinion bearing cups into housing. Place lubricated pinion bearings into cups. Position Gauging Plate (J-23597-11 for 7 1/2" and 7 5/8", J-21777-29 for 8 1/2" and J-21777-85 for 9 1/2" ring gear) and rear pinion bearing pilot on preloaded stud.
  3. Install through rear pinion bearing, front pinion bearings and Bearing Disc (J-21777-42). Tighten hex nut until snug. Rotate bearings to insure proper seating. Hold preload stud stationary with a wrench on flats. Tighten hex nut until 20 INCH lbs. (2.2 N.m) are required to rotate bearings. See Fig 1 .
    Fig 1: Sectional View of Pinion Setting Gauge Set
    G71748Courtesy of GENERAL MOTORS CORP.
  4. Mount side bearing Gauging Discs (J-21777-45) for 7 1/2", 7 5/8" and 8 1/2" or (J-21777-86) for 9 1/2" ring gear on ends of arbor. Place arbor into carrier making sure discs are properly seated. Install side bearing caps and bolts. Tighten bolts to avoid movement.
  5. Position dial indicator on mounting post of arbor, with contact button resting on top surface of plunger. Set dial indicator at zero. Push indicator down on indicator shaft until needle rotates 3/4 revolution to right, then tighten in this position.
  6. Preload dial indicator 1/2 revolution, then tighten in this position. Place plunger onto gauging area of gauge plate. Rock plunger rod slowly back and forth across gauging area until dial indicator reads greatest deflection.
  7. Set indicator to zero. Repeat rocking action several times to verify setting. Once zero reading is obtained, swing plunger until it is removed from gauging area.
  8. Dial indicator will now read required pinion shim thickness for a nominal pinion. Record this reading. Check drive pinion for painted or stamped markings on pinion stems, or for a stamped code number on small end of pinion gear.
  9. If marking is a plus (+), add that many thousandths of an inch from indicator reading. If marking is a minus (-), subtract that many thousandths of an inch from indicator reading. This will then be required thickness of rear pinion bearing shim pack.
    NOTE: If no markings are found on pinion, use dial indicator reading as shim thickness.
  10. Remove bearing caps and gauging tool from housing. Place selected shim pack on pinion gear. Using a press, install lubricated pinion bearing onto pinion shaft.
  11. Install a new collapsible spacer over pinion gear shaft. Position pinion assembly in housing. While holding pinion forward, carefully drive front pinion bearing onto pinion gear shaft until a few threads are exposed.
  12. Install seal, pinion flange, washer and nut. Tighten nut until all end play is removed. Rotate pinion several times to seat bearings. Check preload using an INCH lb. torque wrench.
  13. Continue tightening nut and checking preload until specified preload is obtained. See AXLE ASSEMBLY SPECIFICATIONS  table. DO NOT  back off nut to lessen preload.
  14. If preload is exceeded, a new collapsible spacer must be installed, and nut must be retightened until proper preload is obtained.
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