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Triumph TR6 - Adding J Type Overdrive

I will be adding a J type overdrive to my non overdrive 73 car. I would like to add the overdrive unit to the transmission that I now have as opposed to putting in the complete overdrive transmission from the donor car. I understand that mainshafts are different and that the transmission mounts may have to be added. Any advice on how to do it and what might be involved would be greatly appreciated! Thankyou
Michael McLaughlin

Hello Michael,

Here is a list of the activities involved with installinga JType to your non-overdrive transmission.

1. Dismantle transmission and install overdrive mainshaft.

2. Assemble transmission with JType adapter and the JType overdrive.

3. Install electrical interlock switches in the transmission top cover.

4. Assuming the JType overdrive you are using was originally installed in a Triumph TR6 (not a Volvo or some other make) then the rear housing of the overdrive will already have the mounting holes drilled and tapped and the driveshaft flange will be the correct size.

5. Install the transmission in the car - no change should be needed to the rear mount.

That gives you some idea of what's involved. For that work I had a quote of around $1,800 Cdn not including the cost of the JType unit itself.

Instead I opted for the Toyota Supra 5 speed conversion with Hydraulic throwout bearing system.

Good luck to you and if you are looking for a JType overdrive drop me an email.

John Parfitt
Calgary, Canada.
John Parfitt

I recently did a J-type conversion on my gearbox. I used an overdrive from a triumph sedan (2000). It went fairly easy. Since you have to replace the mainshaft, I used the opportunity to rebuild the entire gearbox and replace the worn items (such as the synchros, gaskets and seals). I have a '76 so there was no problem with the rear mount. I think you may have a problem with the earlier mounts, not sure but it may be pre '73. Also, I had to redrill the holes in the flange to match up with the tr6 driveshaft. A local machine shop did that for me for $5. Wiring was simple. The only mistake I made was not using gasket sealer and not replacing the o rings on the shift shafts (is that the proper term?). Those created a minor leak that would drip on the exhaust pipe and smell. Will only make that mistake once since I had to pull the unit out again. Overall, very glad I made the of difference on the highway.
Mike Parkhill

This thread was discussed on 05/05/2003

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