Jim Smart
April 1, 2000

Step By Step

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Rebuilding Ford’s venerable 8-inch third member is straightforward. All you need is a ring-and-pinion set (if yours is worn out) from Richmond Gear, differential side and pinion bearings, pilot bearing—ironically the most expensive bearing at $33—and the pinion seal.
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Disassembly begins with removal of the adjustment nut lock. A 1/2-inch wrench gets the job done.
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Remove the differential side bearing caps.
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Then remove the ring gear assembly.
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Remove the ring gear from the differential.
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Sometimes the ring gear has to be driven from the differential with a punch. Drive the gear evenly for 360 degrees.
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Divide the differential with a chisel or putty knife.
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Once divided, you can see the side and pinion gears.
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Once the tension pin has been removed, drive out the differential pinion shaft, which runs through the pinion gears.
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Differential pinion shaft wear needs a close look. Abnormal wear is cause for disposal.
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Here’s an exploded view of what makes a differential a differential. These parts allow your Mustang to turn right and left without tire scrub, so to speak. They allow the rear wheels to operate independently. The pinion shaft (A) supports the pinion gears (E). The tension pin (B) retains the pinion shaft. Side gears (C) are tied to the axle shafts. Thrust washers (D) are side bearings for the side gears. Thrust bearings for the pinion gears (F) give these gears something to bear against.
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There are two basic types of pinion gears—one for limited-slip differentials (left) and one for conventional differentials (right). The limited-slip gear has a raised area to clear the clutch pack, but the conventional gear doesn’t. This means you can use the limited-slip pinion gear in a conventional differential, but you cannot use a conventional pinion gear within the limited-slip differential.
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There are also two types of thrust washers that apply to each type of pinion gear.
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Differential side bearings are removed next. All you need is this puller, which can be rented or accessed at your neighborhood machine shop.
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Next, pull the yoke. You might need a puller or a press to remove the yoke.
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The pinion retainer is removed next.
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Sometimes the pinion retainer is stubborn. Drive the pinion assembly out with a punch by tapping the pilot shaft.
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The pinion pilot shaft is a high-wear item and the leading cause of noise. Examine and measure this shaft per the Ford shop manual before going any further.
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Drive out the pinion bearing races (cups) with a punch.
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Use a press to drive in the new pinion bearing races. Take care not to score the contact surfaces.
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The Richmond pinion gear is pressed into a new NAPA bearing.
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Believe it or not, a lot of folks miss this one. Lubricate and install the pinion retainer O-ring.
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The outer pinion bearing is next. Use lots of lubrication (gear lube)...
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...and then drive the pinion seal into place.
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The pinion gear is fitted with a crush sleeve, which allows a certain amount of endplay in the pinion shaft. These crush sleeves must be replaced during service to allow accurate endplay.
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Slip the pinion retainer over the pinion shaft.
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Press the driveshaft yoke into place, and then torque the nut to specs.
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When a crush sleeve won’t cut the mustard, you must resort to a sleeve and shims. Where this differs from a crush sleeve is the use of shims to adjust endplay. Once again, check the Ford shop manual for correct endplay using the tools recommended.
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Install the side gears, making sure you lubricate and install the thrust washers first. There’s one on each side.
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Pinion gears are next. Again, don’t forget lubrication and thrust washers. Drive the pinion shaft through.
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Install the tension pin next, which retains the pinion shaft.
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Install the other side gear and thrust washer, and then tie the two halves of the differential case together.
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Ring gear installation is next.We’ve opted for 3.55 gears. Use the ring gear bolts to pull the gear onto the differential case. We’re using Loctite on the bolt threads for security.
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Then the bolts are torqued crisscross between 65 and 75 lb-ft.
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Differential side bearings are pressed onto the case next. Mitch Jackson uses an old inside roller cup from an abandoned bearing as a driver.
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Here are the completely assembled pinion and differential assemblies for your visual reference.
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Believe it or not, this is the most expensive part, except for the ring-and-pinion gears. The super-small pinion pilot bearing retails for around $35. Seat this into place, and then install the retainer.
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The pinion retainer is shimmed to ensure proper pinion-to-ring gear depth.
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Install the pinion retainer.
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The differential side bearings are next. Lubricate the races and bearings...
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...then seat the ring gear assembly in place.
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Differential side adjusters are installed next. Get the ring gear centered with a smooth marriage with the pinion, and then tighten the adjusters.
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Mitch Jackson of A&M Gear Service checks ring-to-pinion backlash with a dial indicator. Backlash should be between 0.008 and 0.012 inch.
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A ring-to-pinion marriage means smooth lapping of the gear teeth. Jackson paints the gear teeth with a lapping compound designed to show tooth depth and positioning.
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Jackson runs the gears through, and listens for abnormal sounds or binding.
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After the gears are run through several times, Jackson inspects the pattern in the compound.
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This is what you should see—tooth contact that’s centered on the tooth front and back.
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Next, install the differential side bearing adjustment locks.
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Our completed 8-inch differential is ready for installation. Always remember that if you retrofit your conventional 8-inch to limited-slip, you must use a friction additive in the lubrication for best results.
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Jackson replaced our axle bearings while he was at it. Old bearings can be driven off with special tools, but Jackson cut our old bearing off with a cutting wheel. Always wear eye and ear protection for this operation.
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The new axle bearing slips on, followed by the retainer/slipper
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The axle shaft is pressed into the bearing.

Rear axles are something we don't think about often. In fact, rearends are likely the most uninteresting part of a classic Mustang until they fail, or until a sparky upstart blows your doors off at the traffic light, and then you're wishing you had a set of 3.91 gears. When rearends fail, they leave us stranded, or they follow us home in noisy protest.Ford removable carrier differentials perform reliably for thousands of miles with minimal maintenance. Keep the differential serviced with proper lubrication, and you can expect more than a quarter of a million miles without a complaint.We're going to focus on the Mustang's basic V-8 and large six differential—the 8-inch removable carrier unit. The 8-inch differential sports an 8-inch ring gear (hence the name) in a wide variety of ratios ranging from 2.50:1 to 4.11:1. Most common are 2.80:1 and 3.00:1 for small-block Mustangs. We're going to show you how to rebuild an 8-inch removable carrier differential by covering the basics of how to do this in your home garage.At first glance, a differential can be an intimidating sight. It's just downright overwhelming if you've never tried it before. We looked to Mitch Jackson of A&M Gear Service in Southern California for guidance on our 8-inch chunk from a '67 Mustang. Jackson told Mustang Monthly that most differentials wear out due to neglect. He added that the most common wear item is the pinion pilot bearing, which generates the most noise when it fails. If the ring-and-pinion gears are initially properly lapped, they can live a long time, he tells us.