Conversion to 4-Speed


4 speed w engine a.jpgThe 4-speed manual transmission wasn’t offered in the GM compacts until April of ’62, probably about 100 sold in 62 Olds (Jetfire and Cutlass). Less than 500 and maybe less than 200 in ’63 Olds Jetfire and Cutlass. Buick Special and Pontiac Tempest also offered, but I don’t know how many they sold either. They were all Borg-Warner T-10’s. Full size GM’s and Fords used the same transmissions. GM produced 4-speeds didn’t become available until 1964. Made in Muncie, IN thus the nickname “Muncie” 4-speed, or “Rock crusher” (M-21 and M-22’s). Corvette started with the T-10’s in ’57. The Olds T-10 transmissions that I have seen/owned have a cast iron case and aluminum tail section. T-10’s are available with an aluminum case and tail section, however I have only seen them in Corvette’s.

The big difference in Olds F-85 and Buick Special T-10’s is that they have a bolt hole and threads on the output (main) shaft that provides for the yoke (drive shaft connector) to be bolted to the output shaft. This is a MUST HAVE.

4 speed.jpg
You will need a 4-speed drive shaft or at least the front section of the 2 piece drive shaft used in all Olds and Buick to obtain the correct length for the drive shaft. The three speed, 4-speed manual transmissions and automatic transmission are all different drive shaft lengths. The rear section drive shaft is also different for a Jetfire car. It is a two piece, two diameters overlapping each other with a rubber sleeve in between.

The front floor pan is different in a 4-speed Olds and Buick car. The “hump” between the driver and passenger sides is higher and wider to accommodate the 4-speed transmission and shifter. MUST MODIFY non 4-speed cars floor pan to work with the 4-speed manual transmission.

4 speed a.jpgNeed a hole in the back of the crankshaft for the pilot bearing for the front, input shaft of the manual transmission. It is possible that all crankshafts were made with the pilot bearing hole, but I am not positive of this (something to check with D&D) and the swap needs a manual transmission flywheel. There are two different flywheel and clutch set ups. The Jetfire uses a 10″ clutch and the F-85 and Cutlass uses a 9 1/2″ clutch, each with their own flywheel size. Of course you need a bell housing with inspection cover, clutch, pressure plate, throw-out bearing and actuating fork, two pedal set-up with all linkage and springs.

The shifter supplied by GM is NOT very good! I have substituted a Hurst Competition shifter bolted to the transmission and welded the Olds F-85  “pencil stick” operating lever on the Hurst set up to “look original” in the car. The back-up light switch from Hurst also will work, if you have the back-up light option.

4 speed w engine.jpgI have done this twice and many others have done this conversion also. It IS a BIG job!

Good luck………..Jim Noel

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5 Replies to “Conversion to 4-Speed”

  1. Any JETFIRE really needs the 4 speed manual, and the other cars could benefit as well. The 62-63 automatic was a very poor match to the torque curve of the engine, and had plenty of failure modes. At one time I had 13 of the “slim Jims” sitting around, trying to keep a good one behind a 63 engine.
    Bruce Roe

  2. Excellent website. A lot of useful info here. I am sending it tto a few buddiies ans also sharing in delicious.

    And obviously, thank you in your sweat!

    1. I no longer have the specific info on the model or part number for the Hurst shifters/linkage that I used. I do not recall if there was anything specific when I ordered them? I recall that they were Hurst Competition Plus shifters with the linkage kit to fit a Borg Warner T-10 transmission.
      I have just looked at the linkage kits for the Hurst Competition Plus shifter and see that they no longer specify a kit for our little gems. I do believe the kit for the Corvette B/W T-10 will work but would call Hurst to check it out first.

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