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Don't Let Her Rear End Scare You

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Setting up differential gears can be a little scary, but it need not be. Check out this do-it-yourself procedure and save $100 plus. The only special tools you'll need are a depth micrometer and a dial indicator.

The example I'm going to use is an 8" Ford rear end. Let's assume you're going to replace the existing gear set with a new 3.00 or 3.55 or whatever - doesn't matter from a setup perspective. I will assume you have disassembled the gear case, cleaned parts including the new gears and bearings and you're ready to begin assembly. Be sure you marked the side gear bearing caps to differentiate them. Switching the caps will cause a mismatch of the ID threads and make it impossible to install the threaded ring nuts. See exploded view of differential (Figure 1) for nomenclature.

[exploded view]
Figure 1

Install the pinion in the drive pinion retainer

  • Begin by pressing a new Timken cone assembly (inner race) on the pinion. Place the back face of the one assembly against the gear. See the Timken Dimension Sheet (Figure 2) for bearing nomenclature.
  • Press two new Timken cups into the drive pinion retainer. The back face of the cups should face each other in the retainer. These bearings must be pressed in place! Hammering bearings into place can deform them and cause premature failure.
  • Place the pinion in the drive pinion retainer and slide a new collapsible spacer onto the pinion shaft - followed by the second cone assembly.
  • Splash the new bearings with fresh 90w gear oil.
  • Apply a little assembly grease to the seal surface of a new pinion oil seal and press the new seal into the drive pinion retainer. You may carefully tap the seal in place with a hammer. You will want to use a small piece of oak to clear the brow of the retainer.
  • Slide the yoke onto the splined end of the pinion shaft and install the pinion nut. Coat the threads and the back face of the nut with a silicone sealer to prevent oil from leaking out the splined end of the shaft. Hold the yoke in a vice and tighten the pinion nut until a pinion rotating torque is 20-25 inch pounds is achieved. Hold the yoke only to tighten the nut-clamp the retainer to check the rotating torque. This process provides proper bearing pre-load.
  • Install pinion assembly into the differential carrier. I would suggest you not install an O-ring on the pinion retainer at this time to ease assembly and disassembly during this phase of setup. I also prefer to omit the shims between the pinion retainer and differential carrier to simplify calculating the shim thickness in the next section.
  • Torque pinion retainer bolts to 20 - 25 ft. lbs.

[Dimension Sheet]
Figure 2

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