Technical Korner of Our Classic ’63 Starfire Convertible ...



Technical Korner of Our Classic ’63 Starfire Convertible:

Rear End Views

By Jamie Cox and Mike Izzo

We came across an ad in October, 2014 from a company called Fabcraft Metalworks based in Southlake, Texas on their new product called "The Trophy Track Special". This is a purpose built limited-slip or posi-trac differential unit for 1957 to 1964 Oldsmobiles and Pontiacs with the 9.3 inch rear end. The limited-slips were called "Anti-Spin Differential" in our 1963 Oldsmobile literature. Only about 10% of ’63 Oldsmobiles had anti-spin units.

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We do continual upgrading on our collector car in hopes of keeping it drivable for another 50-plus years. Our thought was that by installing this (anti-spin) option our car would be more versatile for any road or weather condition. At the same time, we felt we could change the original gear ratio of 3.42:1 to 3.08:1 for improved mileage through lower engine RPM’s at highway cruising speeds.

Since we had planned a road trip down to Los Angeles in late February of 2015, we coordinated with Fabcraft to send all of the necessary installation components to J & S Gear of Huntington Beach, California. John at J & S has a long history installing Fabcraft products and was highly recommended by Dave at Fabcraft. A New Trophy Track Special limited-slip differential and a used 3.08:1 ring & pinion arrived prior to our Southern California trip. New 3.08:1 gears are not available, so changing from the original 3.42:1 gears requires the installation of “good” used sets. We delivered the car to John at J & S and they did the installation over a 2 day period involving about 6.5 hours labor. Fabcraft Metalworks has applied their vast experience with, and knowledge of, the 9.3 inch Olds / Pontiac rear end and its components to bring all of the appropriate enhancements to the design of the new Trophy Track limited-slip. Compared to what was available 52 years ago, this new posi unit is very much beefed-up, with its gear design and other features including all AISI 9310 alloy steel "pro-gear" internals and a nodular iron case with thicker walls.

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With the installation completed, the car was test driven and all looked great. We did understand the used 3.08 gears installed appeared to be a good set of matched gears producing a very nice wear pattern. After picking up the car to drive it the 56 miles back to our friend Mike’s home, we noticed a "noise" coming from under the car had developed during the trip. It did not sound like a bearing and if we put the car in "Neutral" the noise quit, so it only happened under "load" while driving at any speed. It did "speed up" as we accelerated and stopped when we stopped. We returned the Starfire to John at J & S for analysis. J & S Gear Co. has a great warranty of 12 months or 12,000 miles but does not cover abuse, racing, off-road use, etc..... so it covered this incident.

Over the next week, John went through his checklist to determine the source of our "noise". Where was the noise coming from? Bearings were checked then replaced with new parts…universal joints were inspected then replaced with new units. Even a newly built and balanced drive shaft was installed. The posi unit and gears were inspected for abnormal gear wear and proper tooth contact patterns…and everything looked excellent. Running the car on the hoist offered a quiet test in any gear. The correct gear oil of 85w-140 non-synthetic and correct special friction modifier had been used. J & S Gear even borrowed a "microphone" set-up from the local GM Dealer to try to pinpoint where the noise was coming from. However, noise can easily telegraph from one area to another so that action did not provide any real conclusions. Brad Duerst, Fabcraft's technical engineer, was also consulted along with gear and rear end specialists he has collaborated with for decades, all in search of an answer. Finally, with J & S having pulled the rear end all apart to find no readily defining evidence of anything wrong, Fabcraft decided to air-freight a complete new limited-slip unit and one of their new Vintage Gears 3.42:1 ring and pinion gear sets. By the way, this was all at their expense in order to allow a complete rebuild of our third member by J & S without investing too many additional man-hours or shop time in the "hunt" for the mystery noise.

Speaking of time, my wife and I had run out of time and had to fly back to Canada for key commitments such as Medical Specialist appointments and connecting with a granddaughter arriving from Toronto for her March break and related events. We left our classic car in good hands with Mike, John and Brad knowing they would find the solution.

Once all new replacement parts arrived and J & S Gear had an open shop time spot for our ’63 Oldsmobile, the complete installation was done over again. They even worked Saturday. The Starfire was then extensively road tested with no noise this time. Without spending excessive shop time, we can only assume the used set of 3.08:1 gears, while beautiful to the eye and giving a correct set-up pattern, may have been faulty in some way to cause this noise issue. Mike and a local friend then picked up the car and drove it back to Mike's home with no problems. No added costs from J & S Gears…thank you very much, John.

We did strike a deal with Fabcraft to help off-set the costs of their new Vintage Gears 3.42 ring and pinion…they were a new gear set obviously costing more than the used 3.08 set originally acquired. On March 26th we flew back to Los Angeles to organize taking our ’63 Olds Starfire Convertible home, now safe and reliable once again.

Both of these "classic car sources" acted very professional in our dilemma to solve this particular puzzling noise and they have over 60 of these new limited-slip differential installations done with no issues. We would not hesitate to recommend both of them to anyone in the future looking at rear end changes or specialty gear set-ups…whether to purchase components outright, purchase components assembled or for a complete installation into your car.

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• Fabcraft Metalworks 1360 N. Sunshine Lane, Southlake, TX 76092 USA

Tel # 1-800-208-8242 Fax # 1-817-421-0243 and email:

fabcraftmetalworks@ Attn: Dave Winders or Brad Duerst

Fabcraft Website: fabcraft.cool

• J&S Gear Co. 18222 Gothard St. Huntington Beach, CA 92648 USA

Tel # 1-714-841-4545 attn: John Coulman

email: JSGearco@

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