Mopar 8 3/4 Rear-Gear Buildup - Gearing Up

Fully torque one bearing-cap bolt on each cap, while snugging down the other. Turn the adjusters in until there is a small amount of preload. At the same time, keep a noticeable amount of backlash in the gears. You can feel the adjuster tighten and remove any bearing play. Starting with a large amount of backlash, turn the left adjuster (opposite side of the gear teeth) as tight as you can, pulling on a 12-inch long spanner wrench. Tighten the right-side adjuster to make sure it's tight, and then measure the backlash. Randy's Ring and Pinion recommends .006-.010 inch of final backlash, easily checked with a dial indicator. Backlash should be checked at four different positions by rotating the ring and pinion. If the backlash is too wide, back the right (ring-tooth side) adjuster off a notch, and then bring the left back in to full preload. Again, wrench the right adjuster to make sure it's tight, and recheck. Work the ring gear toward the pinion in this manner until the backlash is within specs. Once the backlash is set, torque the remaining main-cap bolt on each cap.

Use gear-marking compound to check the meshing pattern of the gears (see chart on page 37). This will establish a visual reference of the gear-mating pattern. If the backlash and bearing preload are correct, the only thing that can cause a poor pattern is an improper pinion-depth setting. This means a full teardown to remove the pinion and change the shim. If you get a good pattern, throw it in the housing.

Swapping centersections in an 8 3⁄4-equipped Mopar is a quick and easy process. Start by removing the axleshaft retainer nuts.

The axleshafts should slide out of the housing with little trouble. If they stick, loosely bolt a reversed brake drum onto the wheel studs to act as a slide hammer.

At this point, the centersection can be unbolted and removed. Have a drain pan in position to catch a serious load of oil once the seal to the housing is broken. If it sticks, a floor jack under the yoke will usually break it free.

We used a bead of silicone to provide the seal, balanced the case on a floor jack, and shoved our "fresh" 4.10-geared Sure Grip center into place in our Duster. All that was left was to replace the axles, fill it with lube, and enjoy the punch of gear reduction laying torque to both wheels.