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Vintage Corvette Tech: Swapping the Powerglide for a Ford 3-Speed Manual Transmission

Shift for Yourself

Drew Hardin Jan 8, 2019
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Jack Hardgraves had had enough. A friend bought a Thunderbird “and proceeded to humiliate Jack in front of the crowd at the local dragstrip Sunday after Sunday. The gap wasn’t big, but it was there, so Jack decided to put a stick shift gearbox in place of the automatic unit and go gunning for his fine feathered friend.”

002 Archive 1955 Chevrolet Corvette Ford Transmission Swap Bolting Transmission To Bellhousing 2/6

So began a story in the March 1956 issue of Hot Rod magazine about curing one of the common complaints about pre-1956 Corvettes: the mandatory Powerglide automatic transmission. To get a leg up on his T-Bird-owning buddy, Hardgraves went to Nicson Engineering, a longtime speed-parts manufacturer in Los Angeles. The team there determined “a floor shift model seemed logical, since it would eliminate the necessity of rigging up column-shift linkage.” Hardgraves’ Vette was new enough to have an open driveline, so the Nicson crew decided that a three-speed transmission out of a 1951 Ford truck would fit the bill. It worked with the open driveline, had a floor shifter, and shared a tailshaft and gear ratios with Ford passenger cars. Plus, if he so desired, Hardgraves could employ an old hot rodder’s trick and fill that gearbox with Zephyr cogs.

003 Archive 1955 Chevrolet Corvette Ford Transmission Swap Transmission On Engine On Hoist 3/6

Cook Machine Company supplied a Cyclone bellhousing to join the Ford box to the Blue Flame Six, and the Chevy’s flywheel was drilled to accept a Ford clutch. A clutch pedal was made from a second brake pedal, hung from the same bracket as the brake but offset for room between the two. (Smaller pads on both pedals helped make more room, too.) Rather than using mechanical clutch linkage, Nicson adapted a hydraulic slave cylinder from a Triumph TR-2 and clutch master cylinder from a ’48 Ford.

004 Archive 1955 Chevrolet Corvette Ford Transmission Swap Hole In Floor 4/6

To fit the new setup in the car, Nicson removed the Vette’s stock crossmember, as it sat too far back to support the transmission. A new crossmember was fabricated from 1x3-inch channel iron and located across the fame members just below a hole cut in the floor for the shift lever (and for access to the transmission’s removable top). Because the Ford transmission was shorter than the Powerglide, the driveshaft was lengthened 7 inches by grafting a section of the Ford’s shaft to the original Chevy shaft.

005 Archive 1955 Chevrolet Corvette Ford Transmission Swap New Crossmember 5/6

“After the job was finished, Jack issued the challenge to his friend and was once again accepted,” the story concluded. “This time, though, the tables were reversed. Jack ended up in front of the T-Bird just about the same length he used to be behind.”

006 Archive 1955 Chevrolet Corvette Ford Transmission Swap New Clutch Pedal 6/6

Since Chevrolet had announced the availability of a manual transmission in 1956 Corvette models, this sort of swap “shouldn’t be as complicated as Jack’s was,” the magazine pointed out. “But if you happen to like the idea of a stick shift in your pre-’56 Corvette, you can do it yourself with a Ford transmission and a Cyclone adaptor ring.” Vette

Photography by Eric Rickman, Petersen Publishing Co. Archive

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