Shop Talk: Triumph TR3 Transmission Conversion

Triumph TR3 Transmission Conversion

With today's driving conditions and the fact that parts and transmissions are getting harder and harder to find, we constantly have to modify and update cars for repair. This is often the case with Triumph TR3s. When our client came to us wanting to update his standard 4-speed transmission to an overdrive, we immediately decided the best route to go was the later J-Type overdrive transmission out of a Triumph TR6. We chose the later J-Type for several reasons; one being that the later type transmission is much easier to find and much cheaper than the original early A-Type that the car would have come with. The J-Type also has slightly taller gears that will help with today's increased driving speeds and has the benefit of being a 4-speed synchro.

Triumph TR3 Transmission Conversion

When it comes to installing this later type transmission, it's all pretty straightforward. You can literally bolt this right into place. The clutch, hydraulics, starter, and driveshaft are all the same and will not need to be touched. We do recommend installing a new clutch kit and machining the fly wheel while you're in there. What will need to be modified is the rear transmission mount and exhaust system. Once the transmission is installed, you can use a jack to support the transmission and locate it just where you like it. We used a flat steel plate and a half-inch rubber block to make our transmission mount. We located the steel plate just under the floor boards on top of the frame rails. This way we did not have to cut or modify the floors. Once we knew where we wanted the mount located, we drilled four holes, two on each side, and fixed nutserts into the frame so we could bolt the mount as well. At this point, you can shim the transmission and mount to the desired position.

Triumph TR3 Transmission Conversion

The next step is to get your exhaust to correctly fit the car. Being that this transmission is out of a TR6, you'll notice the original exhaust system may not fit. In our case, the overdrive unit was rubbing on the exhaust pipe. This was a quick and easy fix as we had our local muffler shop cut a one-foot section out of the pipe and shape it just slightly different for clearance.

Triumph TR3 Transmission Conversion

When installing the tunnel and interior back in the car, you'll find it all fits right back into place just like it should. This conversion is undetectable from the interior side of the car, and unless you really know what you're looking at, you won't know it is a later type transmission, even looking from the underside. This is a great conversion and is the best way to go if you want to drive and enjoy your Triumph TR3. Please feel free to leave comments and ask questions.