Part V


Rear Axle Assembly

by John Ironside

(This article was originally published in the June, 2013 issue of the Spark Coil.)

For the rebuild of the rear axle, I decided to replace all the thrust plate pins because most of the pins showed signs of significant wear. The parts order included a pin replacement kit consisting of a drill bit, a 10/32” tap, six screws and six replacement pins. After center punching the existing pin, drilling the pilot hole, tapping the hole, and inserting the screw, the pin was removed with a claw hammer as shown in Photo #1 of the right differential case. A few taps of a hammer set the replacement pins in their final positions. I checked each pin to be sure it did not protrude past the thickness of the outer steel thrust plate and interfere with the center brass thrust plate.

5-1

A properly sized fiber wafer is provided between the right and left axles in the differential to prevent axle end play. Using the existing fiber wafer, the differential case was reassembled and found to have excessive end play. I inserted a new fiber washer (included in parts order) and the differential case was reassembled. There was still too much end play. Fortunately, the parts order included a double set of gaskets for the rear axle. So I placed two new fiber wafers between the two axles, and when the differential case was bolted up, I found that the wafers were too thick because neither axle could be turned.

To get the correct spacing, I had to reduce the thickness of each wafer so the final “wafer sandwich” was correct. Milling the face of the 1” wafers proved to be very difficult. They were hard to hold by hand, and gluing them to the work bench with a hot glue gun didn’t hold very long. Sanding seemed to only roll the edges because the fiber material resisted abrasion. Finally, with a lot of effort, metal files were used successfully to obtain the correct thickness. With the wafers in place, the differential case was bolted up and the cotter keys inserted, and the axles extending out each side of the differential rotated with a firm drag and no end play. The ring gear was then bolted to the differential case, and each pair of bolts holding the ring gear was wired together to secure the installation.

The next task was to eliminate end play of the differential within the housing. With the left housing supported in the bench mount axle holder, the left thrust plates and inner bearing were positioned on the axle and inserted into the left housing. The right thrust plates and bearings were then installed and the right housing positioned so the joint between the housings could be bolted up. My first attempt was too tight, so the right brass bearing plate had to be milled to about 70% of the original thickness. By holding the bearing against the wheel of a bench grinder, I achieved the required thickness.

Photo #2 shows the differential inserted into the left housing. Attached to the housing with three bolts is the drive shaft that is supported horizontally. The initial fit between the pinion gear and ring gear seemed firm, but rotating the drive shaft seemed to be smooth with modest effort. I was told a crescent shaped piece of paper inserted between the gear teeth should create crisp creases without tearing he paper. This is what is happening in the photo.

5-2

Knowing that the adjustments were complete, I positioned gaskets with gasket sealer and the housings were bolted up to the drive train. To align the drive shaft perpendicular to the rear axle, I installed the radius rods and adjusted them until measurements between identical points on the two break hubs to a common point at the universal were identical.

Photo #3 shows the final task of installing outer bearings and seals. Since the inner axle bearings typically receive less wear, I made the decision to switch the inner and outer bearings for the final assembly. Another consideration was replacing the original outer bearings with safety hub bearings. Safety hub bearings are fitted to the axle housing and do not impose load on the rear axles. If an axle breaks, the wheels stay on the car with a safety hub, rather than falling off in the original design. However, the downside is that a pair of safety hub bearings will cost over $500. Since the parts cost of this restoration project was already over $800, I decided to retain the original bearings, making the bearing switch to compensate for previous wear differential. At a later date I may add safety hub bearings as restoration enhancement.

To keep the lubrication in the differential, a seal is first inserted over the axle and into the housing. Rather than the original leather seal, a modern neoprene seal was selected and is shown on the end of the axle in Photo #3. Next, the replacement bearing sleeve is compressed, inserted in the housing, and rotated with the sleeve puller tool until dimples in the sleeve and housing align. This assures that the grease cups on the axle housing align with the holes in the bearing sleeve. Note that the sleeves are designed for the right and left side of the housing and are not interchangeable. Finally, the washer, felt grease seal, and end cap are installed over the axle, tight to the bearing with gasket sealer between the housing and end cap.

5-3

To keep the lubrication in the differential, a seal is first inserted over the axle and into the housing. Rather than the original leather seal, a modern neoprene seal was selected and is shown on the end of the axle in Photo #3. Next, the replacement bearing sleeve is compressed, inserted in the housing, and rotated with the sleeve puller tool until dimples in the sleeve and housing align. This assures that the grease cups on the axle housing align with the holes in the bearing sleeve. Note that the sleeves are designed for the right and left side of the housing and are not interchangeable. Finally, the washer, felt grease seal, and end cap are installed over the axle, tight to the bearing with gasket sealer between the housing and end cap.

Reassembly is now complete. In the next part of the story, I will discuss the experience (with a few unique twists) of installing the drive train back into the car.