View Full Version : GT6 GT6 overdrive question

05-02-2007, 12:26 PM
I received this question from a visitor to my web site. Never having a GT6 with overdrive, I'm not familiar with the options. Here's the question, any help is greatly appreciated...

Good afternoon Jim: I have a 1973 Triumph GT6 Mark 3 and a spare complete transmission with J type overdrive from a 1979 Spitfire (spare for my 1980 Spitfire) Is it possible to merger GT6 engine with J type overdrive / transmission? (GT6 is still whole, easer to ask questions, rather than pull motor to check)

Thanks for your response or any information could share.

05-02-2007, 12:59 PM
A friend and I installed a Laycock J Type OD in my 1970 GT6. It was quite a project. As we know, the J Type is not original to the GT6. It required a bit of cutting to the propshaft tunnel; a modified propshaft; a OD wiring harness (which we fabricated - not particularly difficult); fabricating a new gearbox mounting bracket; repositioning the gearbox mounting bolts and other, mildly vexing items.

I used a "kit" from Quantumechanics in CT ($1,600 + $200 for the propshaft, with a limited warranty), which sadly did not contain all needed components to install the unit. Also, one of the seals failed within about 1,000 miles, but when that happened I no longer owned the car.

On the other hand, the Laycock D-Type is original to the GT6 and in my opinion, entirely adequate unless you intend to thrash the car on a regular basis. The D Type is also less expensive and far easier to install.

For the record, I'm not an advocate of the 5 speed conversions. Installation requires maiming the car; they are not original (very important to some of us), and entirely unsexy, IMHO. The Laycock ODs may not be quite as reliable as a 5 speed, but properly maintained will deliver tens of thousands of miles of driving pleasure. And, shifting the OD (no clutch required) is a thrill in itself and tons of fun to operate. It never fails to wow passengers (how many moderns have seen an OD operate??).

Below is the link to Paul Tegler's website that illustrates when Paul and I installed the J type in my saffron/yellow GT6. The red one is Paul's GT6, a Mark III with a D-type. It took us all weekend and all night Saturday, and Paul is practically an expert on these cars with a fully equipped garage (i.e., this project is NOT for the uninitiated -- amateurs beware!).

All said and done, I think the OD revolutionizes these cars. The reduced cruising RPM on highways is wonderful. The J type has OD in 3rd and 4th, effectively rendering a six-speed gearbox. I had both the column shift and the gearnob switch, just for overkill.

Here's the link: https://www.teglerizer.com/triumphstuff/gt6/gt6jtype.htm

Please let us know how it goes. I hope this is helpful!


Andrew Mace
05-02-2007, 01:22 PM
Possibly of more immediate concern is the fact that one would NOT want to use a Spitfire gearbox in a GT6, OD or otherwise. The Spitfire ratios just aren't suitable. If this were a later three-rail Spitfire gearbox, it might be possible to use its mainshaft and reassemble the GT6 gearbox with the OD unit. But I don't know if that sort of interchange is possible between a GT6 three-rail box and what I'll assume is a single-rail gearbox from the later Spitfires.

Beyond THAT, what Mark said (above)! /bcforum/images/%%GRAEMLIN_URL%%/smile.gif

05-02-2007, 10:49 PM
Thanks for the info. I've passed it on.