Ford 8-Inch Rebuild - Geared Up

Shown here are all the remaining parts required for our differential rebuild. They include all-new bearings and races for the carrier and the pinion, a new crush collar, a pinion seal, and an O-ring. The bearing kit was valued at about $100.

New races are installed into the pinion housing using a bearing race installation tool carefully sized to engage the race properly. Next, all surfaces are coated with grease in preparation to receive the new bearings.

A new outer bearing is installed onto the pinion shaft. Here, the crush collar is added. Designed to collapse as torque is applied to the pinion nut during installation until the proper preload is reached, it cannot be reused if the pinion nut is overtightened. It also must be replaced anytime a pinion seal is replaced.

Loctite was used on the pinion nut before it was installed. Before it sets up, the required rotational force is measured with a torque wrench calibrated in inch-pounds. The desired force is 20-22 in-lb, which will be shown on the dial when the pinion is rotated using the tool. Our first reading came in at 16 in-lb, so the pinion nut was tightened down a little more for a final reading of 20 in-lb. Be careful not to overtighten the pinion nut to begin with because the crush collar will be too small if the assembly has to be loosened because of a reading that's too high.

Over on the press, the replacement ring gear is installed onto the differential. Locating pins are used to ensure that the gear seats with the correct orientation. Once seated, the ring gear bolts were treated with Loctite and tightened down to 65 ft-lb.

With a new pinion seal in place, the pinion gear is gently pressed into position. With each stroke of the jack handle, the technician rotates the pinion housing to prevent binding and to ensure a smooth installation.

With the ring gear in place, the next step is to install the new differential bearings. It isn't necessary to use the press. The bearings are installed using a tube and mallet as shown here.

With the races in place over the bearings, the differential is set into position in the gearcase. Next, the spanner nuts are carefully placed into their threads on either side of the differential bearing races. The main caps are also threaded to allow the spanner nuts to travel in or out in their bore as required. The main caps are tightened to 85-95 ft-lb. A dial indicator is used to check backlash. A setting of 0.008 to 0.012 inch is desired. Backlash is adjusted by moving the differential to the left or right within the gearcase, using the spanner nuts, relative to the pinion gear. Our initial reading was 0.005 inch.

Here, a spanner nut is shown being turned by a shop-made tool to adjust backlash. Using these nuts, the position of the ring gear relative to the pinion was opened up for a final setting of 0.010 inch.

Preliminary tests with the gear-marking compound show the ring-and-pinion engagement is too high on the gear tooth. The pinion housing must be removed and repositioned using a thinner shim. Replacing the shim with a slightly thinner one will move the pinion closer to the ring gear for more complete engagement.

We replaced the shim with a 0.020-inch-thick shim, and this engagement pattern was the result. It's nearly perfect as it has good depth and is right on the center of the tooth.

With the spanner nuts in the correct adjustment, they are secured into position using the locks shown here. Don't forget to use Loctite on the threads.

Trial-fitting the pinion housing doesn't do the new O-ring any good, so we are installing it now that all of the adjustments are complete and the pinion housing is being installed for the final time.

The pinion housing with the new O-ring is installed and fasteners are tightened down to 30 ft-lb. The gearcase mating surface on the housing is cleaned and a bead of Permatex used to provide a positive seal. Here, the centersection is shown during final installation. The retaining nuts were tightened to 40 ft-lb. The axles were installed and the driveshaft connected as well. Finally, we topped off the axle with some 90-weight gear oil. Since we didn't use a locking differential, a friction modifier or other additive is not required. On a quick testdrive, the newly rebuilt rearend delighted us with more responsive acceleration and completely quiet operation.