Will a five-speed box make our Shelby more enjoyable to drive?

Time to move this one to the front burner.

About 12 years ago, we found and then partially restored/lightly modified a 1967 Shelby GT350. This four-speed Lime Gold car is reputed to be one of 11 equipped with both a manual transmission and factory air conditioning.

As time went on, this amazing car somehow got pushed to the back of both our garage and our minds as we went on to other projects.

Blame a clutch problem that developed.

When preparing to fix that, however, some project creep snuck in: Why not replace the original Top Loader four-speed box with one of Tremec’s new TKX five-speeds?

When our longtime partner American Powertrain caught up on initial orders of its mythically popular new TKX, they were able to ship one for our Shelby.

This car has been our go-to car for vintage rallies and tours, especially out West, where the roads are open and the speeds are higher. The thought of installing a five-speed for relaxed cruising sounded perfect to us.

An invite to Lee Cross’s early GT350 tour prompted us to get going with the swap.

More to come.

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wspohn SuperDork
10/26/23 10:36 a.m.

Unless they revise the lower ratios, the only thing you might get with that swap is an OD ratio above the 1.0 4th gear.  Very nice mod if you find highway travel gets  bit tiresome with the stock 1.0  ratio and whatever diff is in the car,  but not much benefit if you are never topping out 4th or at least running at a speed (likely illegal) that results in an unpleasant noise level.

If one is after performance rather than comfortable cruising, they are well worthwhile - it means that you can drop the diff ratio for better acceleration while retaining top speed capability of the original stock diff.  I ran a close ratio set of gears plus and overdrive in my MG race car that allowed me to go from a 4.3 to a 4.55 which resulted in significantly better acceleration plus the same top end.  I also enjoy the 6 speed box in my Z4M - gives you a very close ratio set for the first 5 gears (5th is 1.00)  plus a nice long cruising overdrive 6th speed.

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