Before the Ford 9-inch became popular, the hot rodder’s choice for a tough rearend was the
In the ’50s and ’60s the search for high-performance parts usually meant a trip to the wrecking yard to rob components, engines, out of big, powerful cars of the day—Chryslers, Fords, Cadillacs, Olds, Pontiacs, and W-Chevys were all used. But when it came to rearends, the overwhelming favorites were those our of ’57-64 Pontiacs and Oldsmobiles.
These rearends were the Hotchkiss style, which means the ring-and-pinion gears, along with the differential components, are housed in a removable carrier, making gear changes and axle replacement quick and easy. They were tough with 9.3-inch ring gears, big pinion shafts, and large-diameter bearings and tough axles. In 1958 a good thing got better when limited-slip differentials were offered. Pontiac labeled theirs Safe-T-Trac while Oldsmobile called it Anti-Slip.
These are the axles commonly used in Pontiac/Olds rearends, (left to right) a factory 29-s
Bigger engines introduced in both Oldsmobiles and Pontiacs for 1959 prompted the second generation of these rearends with 31-spline axles, which were reportedly 22 percent stronger than the previously used 29-spline shafts. During the production run a third-generation gear case was introduced, oddly enough with slightly smaller pinion bearings, which was probably a cost-cutting move. Other changes were made to the limited-slip carrier, but strength was not adversely affected. Another factor that made these rearends popular was the wide selection of factory gear ratios available, 2.56:1 through 4.30:1 while even lower drag racing cogs were available from aftermarket suppliers.
(Left to right) These ring gears are P/O 9.3-inch, 2.69:1; Ford 9-inch 2.75:1; and a Chevr
Pontiac/Olds rearends had been widely used full width under Gassers and other cars and even though lots of slingshot dragster pilots had their legs draped over a narrowed version, custom-width rearends were seldom seen in other applications and almost never under a street car. The simple cure when using wide tires with a stock-width rearend was to radius the fenders and let the tires hang out in the breeze. On early street rods it wasn’t unusual for the rear of the car to be jacked up so wider than stock tires could protrude several inches past the fenders, but then styles changed and the need for a narrower rearend that was reasonably strong led many hot rodders to the ’57 Ford 9-inch, particularly those under wagons and Rancheros as they were the narrowest.
As the popularity of the Ford 9-inch increased the P/O 9.3 began to fade from the scene. Ironically the heavy-duty nature of the 9.3 worked against it and played a part in its demise. Compared to the Ford, the P/O parts were more expensive. By 1965 GM replaced the 9.3 with a Spicer design using an 8.875-diameter ring gear that mounted the internals in the axle housing rather than a separate carrier. The P/O rearend and parts were getting harder to find and there were more Ford 9-inchers being made every day.
The difference is pinion shaft and bearing sizes between these rearends is dramatic; (left
Today finding a P/O 9.3 may take some searching and it’s helpful to know what to look for. Six rib cases will be found on ’57 and ’58 rearends, ’59-64s have seven ribs. Housings with leaf springs were used under Pontiac and Olds in 1957 and Olds only in 1958-60; Pontiacs had coil springs in 1958-60 and from 1961-64 both had coils. Pontiacs had 1.75-inch-wide drums in 1957-58 while Olds used 2-inch from 1959-on, both used 2-inch brakes.
For a variety of reasons, not the least of which is the current Gasser craze, Pontiac and Olds rearends are enjoying renewed popularity. Thanks to the efforts of the Fabcraft Metalworks crew all the parts necessary to rebuild one are available along with a selection of improved components and special tools to make working on them easier. Fabcraft can also supply an excellent manual that tells you everything you need to know about these rearends, along with instructions on overhauling them, or they’ll refurbish a rearend for you.
These are differential side bearing caps. (Left to right) The P/O 9.3, Ford 9-inch, and Ch
In their day Pontiac and Olds rearends had a well-deserved reputation for toughness and reliability, that’s why they were found under so many hot rods on the dragstrip and the street. If you’re building a period-correct car, especially a Gasser, they are undoubtedly the perfect rearend for today.
Some of the most frequently asked questions regarding the Pontiac/Oldsmobile 9.3-inch rearend:
Q: Are parts available?
All P/O third member cases have casting numbers at A; first-generation cases have the date
A: Fabcraft Metalworks provides virtually every component for the Pontiac/Oldsmobile 9.3-inch rearend.
Q: What cars did they originally come in?
A: They came in all fullsize Pontiacs and Oldsmobiles from 1957-64.
Q: How are they identified?
A: By casting numbers and date codes, along with other external characteristics, all of which are shown in the manual by Zach Davidson and Brad Duerst.
Q: Are Pontiac/Olds rearends the same?
A: Starting in 1937 Pontiac and Oldsmobile rearend designs slowly began to converge, to the point that in 1957 all major components were virtually interchangeable, with the exception of some brake components, suspension attachments, and axle housing/axle widths.
Q: How strong is it?
Factory axles are easy to identify: (left to right) Olds 29-spline, Pontiac 29-spline, Old
A: Extremely strong! While the Ford 9-inch is the perceived benchmark of popular rearends today, in stock form the edge would go to the Pontiac/Olds. With its larger bearings, larger gears, and larger axles, the P/O 9.3 would fall somewhere between the Ford 9-inch and the Dana 60 in terms of strength.
Q: Why do Pontiac/Olds 9.3 parts cost more than those for a Ford 9-inch?
A: Ford 9-inch is like the small-block Chevy of rearends. Many Ford 9-inch parts are made offshore; they have smaller bearings and smaller diameter gears requiring less material. The high-volume production runs of Ford-9 inch components allow them to be relatively inexpensive. Pontiac/Olds 9.3 parts are manufactured in the United States and are made in smaller custom production runs using high-quality alloys and the best materials available. These smaller volumes and domestic content result in slightly higher prices.
Three different types of carriers will be found: A is a standard open drive, B is a ’58-63
Rare items today, Mickey Thompson offered lightweight differential cases for drag racing:
These are crush sleeves used to preload the pinion bearings: ’57-62 on the left, ’63-64 on
A shortage of P/O parts isn’t an issue thanks to the team at Fabcraft Metal Works. They’ll
A worthwhile improvement is the installation of a solid spacer and shims in place of the c
Here’s a comparison of the features found on P/O, Ford 9-inch, and GM 12-bolt rearends.