The 8 3⁄4-inch rear was only offered in A-Bodies with the oddball small-bolt pattern, and these rears were fitted with narrow A-Body-only brakes. Here we have a stock A-Body 8 3⁄4-inch with the narrow factory 10x1 3⁄4-inch brakes (left). Notice the huge difference in area when compared to the common 2 1⁄2-inch wide brakes used in most other Mopar applications.
One of the odd things about pre-'72 Mopar A-Bodies was the use of five lightweight 7⁄16-inch wheel studs on a small 4-inch bolt circle. While Chrysler used the common 4 1⁄2-inch bolt pattern and beefy 1⁄2-inch studs on virtually every other car line (the early Imperial's 5 1⁄2-inch pattern being a notable exception), the early A-Bodies were saddled with an econo-box wheel pattern. Going back in the genealogy to the A-Body's origins, as Chrysler's compact economy entry in the early '60s, the five-on-four pattern didn't look so bad compared to the competition's compacts, which usually sported even more miserly four-bolt patterns.
In terms of function and durability in a stock vehicle, the smallish bolt pattern really presents no problems. The hang-ups begin when modifications to the factory package are thrown into the mix. Want to upgrade from the skinny, factory-fitted 13- or 14-inch wheels? Sorry, dude, the oddball "five-on-four" pattern has been all but forgotten by the aftermarket. If large modern rubber, or a serious set of drag slicks, are part of the plan, shelling out for special-order, or one-off modified wheels are about the only option if the stock small pattern is retained. Even then, if the wick has been turned up enough to produce serious dig off the line, you have to ask yourself, "Are those puny wheel studs up to the task?"
To go with the narrow brakes,...
To go with the narrow brakes, the A-Body 8 3⁄4-inch used axle shafts with a unique narrow backspacing. A-Body shafts will not provide the correct spacing to allow the use of the common big car brakes. The different backspacing can be seen here.
In 1973, the big-bolt pattern was finally made available on disc brake-equipped A-Bodies. Previously, the disc brake option consisted of the small-bolt pattern Kelsey Hayes four piston fixed caliper brake set-up, unique to the A-Body car line. The "new" brake set-up brought in for '73 was basically an adaptation of existing large-car components to the diminutive A-Body line. With the large car disc brakes also came the "big car" five lug on a 4 1⁄2-inch bolt pattern, and stout 1⁄2-inch wheel studs. Of course, to go with the large pattern up front, the rear was also revised to include the same large bolt pattern, as well as off-the-shelf "big car" drum brakes, replacing the skinny rear binders previously used exclusively in A-Body applications.
The new '73-and-up large-pattern A-Body rear brakes, B-, C-, E-, F-, J-, M-, and R-Body, as well as 1⁄2-ton light truck rear brakes as fitted to 8 1⁄4-, 8 3⁄4-, and 9 1⁄4-inch axles all interchange. The most common sizes of the big-car brakes were 10x2 1⁄2-inch and 11x2 1⁄2-inch and, with the exception of different parking brake cable lengths, are a bolt-on with any of the above mentioned rears. Of the A-Bodies produced after the change-over in 1973, the vast majority were disc brake-equipped, making the late-style brake hardware a very popular swap in earlier A-Bodies.
A second mismatch unique to...
A second mismatch unique to the A-Body was the small diameter center register found on the face end of the axle shaft (A). All other 8 3⁄4-inch flange type shafts used the same large spec register (B) to locate the drum concentric with the shaft. Notice that the flange face on the large bolt pattern shaft (left) is much larger than on the stock A-Body piece (right). The small face of the stock A-Body shaft gives just enough material to be redrilled to the large pattern.
If your plan is to cut and...
If your plan is to cut and re-spline a set of large-pattern shafts to the A-Body length, make sure that the shafts to be modified are not tapered down in the area where the splines need to be cut. Most 8 3⁄4-inch axle shafts are turned down just aft of the splines (A), and also step down in diameter along the length of the shaft (B). There were so many variations on the shafts, the only sure way to identify candidates for re-splining is to physically measure them.
Our conversion was done by...
Our conversion was done by ordering a set of Moser's custom-forged axles, spec'd for the A-Body 8 3⁄4-inch with backspacing for the common large car brakes. Parts for the A-Body narrow brakes are no longer stocked by most auto parts, and the large brakes offer a huge gain in swept area. The penalty? The rear width grows by about 0.4-inch per side.
The factory axle shaft used...
The factory axle shaft used tapered roller bearings and required that the preload be set with an adjuster, factory-fitted to one side only (arrow). The Moser shaft came with straight roller bearings, which require no pre-load adjustment. Just bolt 'em in and go. The setups are interchangeable.
The factory axle shaft used...
The factory axle shaft used tapered roller bearings and required that the preload be set with an adjuster, factory-fitted to one side only (arrow). The Moser shaft came with straight roller bearings, which require no pre-load adjustment. Just bolt 'em in and go. The setups are interchangeable.
Our rebuild and bolt pattern...
Our rebuild and bolt pattern conversion began with a bare housing, originally fitted with the early-style (pre-'65) tapered output axles with separate hubs. Late flanged axles were a bolt-in changeover. The housing was blasted, and then cleaned spotless, inside and out.