Upgrade A '71-'73 Rearend And Suspension

When Bill Thomas builds a differential, he uses only genuine Timken bearings and seals. He examines bearing races and rollers closely for scoring. During assembly, the bearing gets a liberal amount of assembly lube.

Bill stresses proper treatment of seals and gaskets to prevent leaks. Surfaces must be clean and free from scoring. The O-ring seal has axle lube and is ready. Pinion depth has been checked.

Bill installs the yoke and runs the locknut down. Loctite was used on the pinion carrier bolts, which are torqued to 30-45 lb-ft.

When building a rearend, always use a thread locker for added security. Loctite 262 is a high-temperature thread locker to use in conjunction with proper bolt torque.

Make sure surfaces between the ring gear and differential are free of debris and scoring. Any irregularity will cause ring gear misalignment and failure.

Bill seats the differential and ring-gear assembly in the carrier for setup. Bearings must be lubricated at this point with assembly lube.

Differential side bearing retainers are installed, then screwed down to secure bearings and mate the ring and pinion. These adjusting nuts call for a special spanner wrench. One of them is left-handed thread, which enables the ring gear to be moved left or right to adjust gear backlash.

Bill sets the backlash, which is 0.008-0.012 inch via a dial indicator.

Backlash and gear tooth depth is checked via this yellow compound designed specifically for gear lapping. This is how the gear tooth pattern should look, right smack in the middle of each tooth. Contact should be dead center in pull and coast.

Once backlash and gear depth are set, side-bearing retaining nuts should be torqued to 12-25 lb-ft. Here, Bill installs side bearing adjustment nut locks. Don't forget Loctite on these.

Our N-case Randy's Ring & Pinion 9-inch Trac-Loc differential is ready for installation.

Our '71 Mustang SportsRoof came from the factory with a 302 two-barrel V-8 and 8-inch peg leg rearend with 3.00 gears. We're going to fit it with a Bill Thomas 9-inch housing, N-case Trac Loc, 31-spline axles, and new drum brakes.

First, disconnect both rear shackles and support the 8-inch axle with a floor jack. Our Mustang is already supported with jackstands in the interest of safety.

Disconnect both shock absorbers at the leaf-spring brackets.

You'll have to remove the rear seat to get at the top mounts, which are also stud mounts.

With the rear axle properly supported...

...remove both leaf-spring brackets.

Both front leaf-spring mounts are removed with a 3/4-inch socket and box-end wrench. It's a good idea to spray all hardware with a penetrating lubricant such as WD-40 before you begin work to break down corrosion.

With the rear axle properly balanced, roll the entire assembly from underneath the body. This means you never have to lift anything. It's always good to have a buddy's help with this

Leaf-spring installation begins at the forward mounts. Use liberal amounts of chassis lube on the bolts and bushings to reduce corrosion risk and provide lubrication.

We're installing the new Bill Thomas 9-inch the same way we removed the 8-inch. Use a floor jack and roll the axle into position. Elevate the axle higher than the leaf springs, relying on a buddy to maintain balance.

When installing shackles, use chassis lube or white grease on the bushings for ease of installation.

Lower the rear axle onto the leaf mounting points.

After you secure the leaf springs and torque the plates to 30-45 lb-ft, install both Grab-A-Trak gas shocks. Remember to turn them upside-down and bleed them before installation. Tighten shock mounts to where rubber bushings expand to washer circumference. Don't overtighten.

Install the parking brake cables and brake lines. Now is the best time to flush and bleed your Mustang's brake system.