One advantage to starting with a complete rearend is having the stock axles for reference. Most axle manufacturers have databases to look up specs for particular applications, but most will also advise that variations in factory specs are common, so measuring is a good idea. We measured from the face of the axle flange where the wheel bolts on to the tip of the splined end and found 2958 inches. | 
If you know how to set up a rearend, you're ahead of the game. We don't, so we went to Tim Moore of Moore Automotive, since we know he's assembled numerous axles over the years, particularly GM Salisbury units. Tim prefers starting with a complete rearend so he can retain the factory shims. His first step is to mark the retaining caps for position before removing the stock components. |
Next, the stripped axlehousing is mounted to a shop vice via a custom plate that Tim bolts to the lower cover-mounting bolt holes. After assembling the new pinion gear with the original shim and the new bearings, Tim installs it in the housing without a crush sleeve and then uses a tool from T&D Machine to get an initial pinion-depth reading. | 
One of the key elements to our buildup is the Eaton heavy-duty limited-slip differential. Eaton manufactured the factory posi units for GM cars back in the day, and the unit we're using is similar, having clutch plates to link the drive axles. But this one is more stout, using carbon-fiber clutches and four coil springs for pre-load rather than a single S-spring. It's available for either the stock early 28-spline units or the later '88-up 30-spline. We're going with the 30-spline as an upgrade. |
The car this axle will go in sees lots of street use and has a fairly torquey small-block, so we picked a 3.42:1 ring-and-pinion set for a good balance of street and performance. The new Yukon gears came from Randy's Ring & Pinion and include a detailed instruction manual for those who intend to handle the install themselves. After Tim deburrs the new ring gear and the mounting surface on the new differential, he mounts the ring gear. | 
Once the new bearings are pressed onto the carrier, the differential assembly can be test-fit to the housing. Tim places the factory carrier shims in their original positions and taps the diff into place. The snug fit in the housing is a good indication that the carrier bearing preload is correct. |
With the differential bolted in place, Tim sets up a dial indicator and checks the backlash between the gears. Tim has a fixture that bolts to the pinion yoke to hold it steady so as not to give a false reading. The specs call for between 0.006 and 0.010 inch, and we had 0.008--solidly in the middle. | 
The next step is to "run a pattern" between the gears. This entails coating a section of ring-gear teeth with a special colored paste that has a consistency similar to lithium grease. When the ring-and-pinion mesh, the paste is displaced from the teeth at the point of contact, illustrating the mesh pattern between the two. Ours came out in a nice, centered pattern, indicating that everything was right where it should be. Usually, it will take several tries with varying shims to get it just right, but we got lucky. |
Once the proper gear pattern was established, Tim was able to remove the differential and then the pinion so that the crush sleeve could be installed for final assembly. Setting the proper preload is a matter of tightening gradually while intermittently checking preload with an inch-pound torque wrench. Tim is able to get it just about there by feel and then verifies it with the torque wrench. | 
An alternative to typical production-oriented crush sleeves (left) is the solid pinion spacer, produced by Ratech and available through Randy's. The solid spacer comes with a series of shims, and the installer must use the proper number of shims to obtain the desired preload. The advantage is an increase in strength and the ability to remove and reinstall the pinion yoke without having to replace the crush sleeve and then reestablish preload. This comes in handy when replacing pinion seals. The spacer costs only $17, but installing it takes a little more work. |
We sealed the cover on our fortified 10-bolt and then slipped in a fresh set of axleshafts from Dutchman Motorsports. These are stock C-clip type, but made from an induction-hardened alloy prior to machining for increased durability over stock parts. Our 30-spline upgrade axles should actually be an off-the-shelf application for a '67-'69 Camaro 12-bolt. Randy's recommends using synthetic gear lube and driving nice and easy for the first 15-20 miles, followed by a cooldown period. The next 500 miles should be standard street driving to break everything in, but after that, we should be able to hit this unit pretty hard without fear. | |