|Of the three drivetrain components, the engine, transmission and rearend, it is arguably the rear axle that receives the least attention. Perhaps we focus on the engine because it is more common to run into problems there, and is where much of a budget is spent.
Of the three drivetrain components, the engine, transmission and rearend, it is arguably the rear axle that receives the least attention. Perhaps we focus on the engine because it is more common to run into problems there, and is where much of a budget is spent. Maybe the transmission’s physical connection to our right hand commands it more attention. For whatever reason, the ring and pinion are often neglected. It’s too bad, because, a gear swap or rear axle upgrade can often bring forth some of the most satisfying results, often requiring relatively little cash expenditure.
This tendency is worsened when a project includes a rearend that has little support from the aftermarket. Obviously, those with a ten or twelve-bolt Chevy, a Ford nine inch or the more common offerings from Chrysler and Dana will have options. However, many units have seemingly gone by the wayside.
One of the more notable instances involved the 9.3 inch Pontiac/Oldsmobile rearend of the 50’s and 60’s. An extremely tough and popular rear end in its day, the 9.3 was pushed into the pages of history as more modern units became more widely available.
Until recently, it was nearly impossible to obtain quality aftermarket parts for these rear ends. Restorers were forced to utilize worn parts. Nostalgia drag racers commonly used Ford or GM units in place of their seemingly obsolete 9.3.
Thankfully, with the help of companies such as Texas-based Fabcraft Metalworks, the 9.3 is once again a practical option for anyone building a period correct project car, or a torque monster in need of a tough rear axle. The company offers high quality made-in-America components for these rear ends including ring and pinion sets, axles, rebuild kits and many other stock and performance parts.
Before you tackle an overhaul of a 9.3, it is imperative to know exactly what you have on hand. There were several changes made throughout the years the 9.3 was produced, as well as some part interchange issues that will undoubtedly confuse and frustrate anyone who lacks the information covered below.
The 9.3 debuted in 1957 in Pontiacs and Oldsmobiles. Both makes had shared the same axle in the past, and the new unit used some of the basic geometry of its predecessor. The new rear end was a Hotchkiss (dropout third-member) type using a 9.3 inch ring gear and 29 spline axles intended to manage the power of the newest V8 engines. In 1958, an optional limited slip differential was offered by Pontiac as the “Safe-T-Track” and by Oldsmobile as the “Anti-Spin.”
In 1959, more cubic inches arrived in the form of the Pontiac 389 and the Oldsmobile 394, so 31 spline axles were introduced in an updated center section casting to compensate for the additional grunt. The 31 spline pieces were estimated to be 22 percent stronger than their already stout 29 spline counterparts.
This second progression of the 9.3 was employed for the next four years, but in 1963, it saw another alteration in which pinion bearing sizes shrunk slightly and minor changes to the shape of the case were made. Finally, in 1964, the two-halved Safe-T-Track /Anti-Spin differential became a new, one piece design for that year only (1).
By 1961, Pontiac had introduced the Tempest along with Oldsmobile’s F-85. These models became the first cars built without the 9.3. Due to the high cost of manufacture, the 9.3 saw its last production in 1964.
In its eight years of production, the 9.3 housed production ratios from 2.56:1 through 4.30:1. Even deeper ratios were available over the counter to performance enthusiasts and racers.
In any conventional gearset, a higher ratio will mean that the head of the pinion is larger in diameter, because of its higher tooth count. As a result, the ringgear must be located further from the pinion as gear ratio increases.
To accommodate the array of gear ratios, engineers designed three unique series of carriers, open or Safe-T-Track/Anti Spin, that each fit a grouping of ratios. The three series’ ringgear flanges were of different depths to provide proper spacing of ringgear to pinion (1).
As drag racing flourished during the Sixties, the 9.3 developed a reputation as an exceptionally durable unit. Although the popular Ford nine inch axle also made its debut it 1957, the 9.3 had become the rear end of choice for many of the most demanding applications.
It was a popular swap for hot ’55-‘57 Chevys and was built into dragsters and gassers everywhere. With over-the-counter parts available at the local dealership, junkyard cars widely available and aftermarket parts abounding, the 9.3 flourished into the Seventies. However, as other more modern axles rolled off the production lines, the 9.3 slowly began to fade away.
For the sake of comparison, the super-successful Ford nine inch rear end can provide a helpful illustration of the 9.3s strengths. The Ford nine inch is similar in size and basic design.
Starting from the front, the 9.3 utilized a strong 13 spline yoke. Aside from a slightly smaller dust shield in ’63-‘64, the same yoke was used throughout production on every 9.3. Behind this yoke, the two pinion bearings were housed within the tough, nodular iron case. The 9.3 did not use a separate front pinion support like the Ford did. However, the pinion bearings are very large, much larger than their Ford counterparts, and the pinion shaft is heavier and longer than a Ford’s, which spreads the bearings apart farther, providing exceptional stability (2). The pinion of a 9.3 enters the case very high, and while this slightly reduces overall tooth contact, it provides a mechanical advantage over the lower-set Ford pinion. Finally, holding the carrier assembly in place are two very sturdy caps (3).
The 9.3, with its superior materials and craftsmanship, is a very robust unit. It is structurally sound and has been proven time and again, surviving in some of the most abusive environments.
There are many reasons why one might need to identify a 9.3, and Pontiac and Oldsmobile made it easy for the average guy to determine exactly what he had, provided he had the following information.
To begin, here’s the knowledge one might need if he were searching barnyards, junkyards or riverbanks for a diamond in the rough. As mentioned, the 9.3 case came in three variations, the ’57-’58, the ’59-’62 and the ’63-’64, which will be referred to as the first generation, second generation and third generation, respectively.
First, however, there are a couple of facts to note that may help identify a 9.3 from a different unit before getting too dirty. Obviously, crawling underneath a ’57-’64 Pontiac or Oldsmobile is a good bet, but sometimes the car itself may be absent. In this instance, look at the rear of the axle housing and note its shape (4). Next, count the number of nuts holding the third-member to the housing. There should be ten, but don’t confuse this with the rear inspection cover of a 10-bolt GM axle. On a removed third member, count the number of bolts holding the ring gear to the carrier. There should be twelve.
If the above criteria are met, use the following to verify that the unit is indeed a 9.3, and then to find out exactly what type it is. Not only did the three generations of cases differ visibly, but all Pontiac and Oldsmobile units were cast with raised characters denoting a casting number and date code.
Cases were also stamped at the factory with a code indicating gear ratio and whether or not the unit came equipped with a Safe-T-Track/Anti-Spin differential. Additionally, paint codes on the case and the ends of the axle shafts were used to indicate ratio and differential type. Safe-T-Track/Anti- Spin equipped units also possessed a tag indicating so.
To positively identify a 9.3 case, find the casting number. It is located at the 9 o’clock position between two mounting holes as viewed from the front. The casting number will indicate if it is a first, second or third generation case. A casting number of 522498 identifies the first generation, 535200 and 534548 identify the second generation, and 543317 identifies the third generation.
Next, find the date code. On first generation cases, it is at the 3 o’clock position, but higher on the case, closer to the snout. Second and third generation cases have the date code next to the casting number. The date code will be a letter followed by two or three digits. The letter corresponds with the production month beginning with A for January, B for February and so on, skipping the letter I. The next digit or two digits indicate the day of the month. The last digit is the last number of the production year. Thus, a date code of “E 17 9” reads May 17, 1959 (5).
Finally, cases were hand stamped after assembly with a code indicating gear ratio and differential type. The first number corresponds to a ratio, and is followed by the letter L if it was equipped with Safe-T-Track/Anti-Spin differential.
This stamp is located on a pad near the mounting hole at the 7 o’clock position. Above this stamp and under the nut at the 9 o’clock position will be the tag. Again, note that tags were only found on Safe-T-Track/Anti-Spin cases. The stamp and tag were located near the fill plug. This was done to ensure that service stations used the necessary friction additive in limited slip differentials when changing gear oil.
To supplement the stamped code, cases were paint coded with a color daub indicating gear ratio and an additional green daub if it was a Safe-T-Track/Anti-Spin differential. Unfortunately paint daubs are often faded or gone from original rear ends.
It is simple to verify that the ratio matches the code stamped on the case. Simply count the number of teeth on the ring gear and divide by the number of teeth on the pinion.
Visible differences between the three different cases are relatively easy to spot. The first generation case had six ribs extending from the snout to the flange. The second generation case used seven ribs extending to the flange. These ribs were common to the third generation case as well, but the three parallel ribs were lengthened slightly for two reasons. The third generation case began using smaller diameter pinion bearings which decreased the diameter of the case snout, thereby lengthening the ribs slightly. Easier to spot is the widened driver side portion of the case’s flange. This allowed the three ribs that extended to it to be lengthened slightly (5).
Axles also distinguish a Pontiac from an Olds rear end by the number of drive dogs used in the axle machining process. These are located in the center of the outside end of the axle. Olds axles had two, and Pontiacs had four. If the axles are clean enough to see paint, note the color or colors denoting ratio and differential type. It is also important to note that passenger side axles through 1963 used left-hand thread lugs. These lugs have an “L” on their end. Due to width changes throughout years and models, axles should not be interchanged.
The center sections themselves did not differ between Pontiacs and Olds. Remember that all three generations of cases will interchange among all axle housings, Pontiac or Oldsmobile, assuming spline count within the carrier matches the spline count of the axles, and correct length axles are used.
To add to the density of this information, there was a significant amount of overlap throughout the eight years of production. In some rare instances, date codes may indicate a year that does not correspond to the physical shape of the case.
Furthermore, these numbers may not match the year of car from which they came. Regardless, by using all methods of identification, it is easy to obtain the correct parts.
Once you have identified what you have, you will be able to decide precisely what you need. Fabcraft Metalworks offers ring and pinion sets in many ratios. The most popular ratios, however, are manufactured to fit the most common carriers. Therefore their sets may not necessarily match the equivalent factory gears. Regardless of what you have, Fabcraft is almost always able to get you exactly what you need for your project.
In addition to their array of 9.3 components, Fabcraft also offers a 3.55:1 ratio gearset for the 1965-1976 full-size Pontiac and Oldsmobile cars. 3.42:1 and 3.64:1 ratio gearsets are available for the 10-bolt Buick rear end used in the GS and GSX cars, and a 4.33:1 ratio gearset is offered for the Ram Air GTO.
A comprehensive manual on the Pontiac/Oldsmobile 9.3 is currently in the works. It will include even more details on identification as well as teardown, rebuilding and performance information. To get your name on the list to receive this book, contact Fabcraft Metalworks at 800-208-8242 or email a request to firstname.lastname@example.org. www.fabcraftmetalworks.com