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how hard is it to add overdrive?

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Will_Ringrose

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I was thinking today when on the highway going to work. "It would be nice if the RPMs were lower going 65MPH." Then I remember the overdrive units. How hard would it be to add an overdrive to a Late 73 GT6?
 
I encounterd the same problem of high revs when traveling the highway in my TR6. I opted to make the conversion to a Toyota 5-speed. The conversion was straight forward and easy.
No leaks, and a dependable Toyota transmission.
Just a thought.
 
Gliderman8 said:
I encounterd the same problem of high revs when traveling the highway in my TR6. I opted to make the conversion to a Toyota 5-speed. The conversion was straight forward and easy.
No leaks, and a dependable Toyota transmission.
Just a thought.
Click to expand...

What all is involved with that? Is there a kit I can get? I saw one for the ford type 9 transmission, is it the same idea?
 
I am restoring a 1966 MK2 Spitfire and decided to swap out the 4 sp trans for an O/D trans during the process. In an early Spitfire you have to replace the trans mounting plate (might be the same on your GT6), the drive shaft (needs to be shorter), as well as adding an O/D relay and switch. Since the car was being restored it wasn't that difficult to add the O/D. The issues with an O/D are that you have to find one that's serviceable. Then you either trust that it works, or have it rebuilt. All of the other parts I found through regular vendors. I went with the O/D because I wanted my car to be fairly close to original. Good luck with your choice.
 
Well the way I have always looked at redoing this GT6 was the idea that the original owner would have done the mods. so anything from the day it was new up until 85. A trans swap or an O/O would both be OK with me. It just is really a matter of cost and ease of install.

Without a work space to do the job in, I have to do the work in my driveway that is on about a 25 degree angle.
 
Not that OD isn't desirable on most any Triumph, but I've long questioned the "need" for it on a GT6. I put many miles on both '70 and '72 GT6s and never felt that the engine suffered in any way at highway speeds. After all, 70 mph in a stock GT6 works out to right around 3500 rpm. While maximum horsepower was developed somewhere well north of 5000 rpm, maximum torque came usually around 3000 rpm.

Sure, an OD gearbox will drop the revs and save some fuel (and maybe a bit of engine wear), but it'll take years for the OD to pay off in that sense. And yes, it's also a bit more fun to have more gears, but that six is strong and flexible enough that it doesn't really need it.

Often as not when a GT6 was factory equipped with OD, the diff. went from a 3.27:1 to 3.89:1.

I guess it's all what you really want; I never "missed" having it on my GT6s. Spitfires and Heralds certainly can make good use of it, though, as their gearing makes for much higher revs at highway speeds....
 
Question for those with the Toyota 5 speed conversion. How does the Toyota tranny feel compared to the Triumph tranny? I really like the short thows and feel of the Triumph tranny, would that change with the Toyota?

I'm open to either configuration; just trying to gather as much info as possible, and I know this part is subjective.

Thanks,

Eric
 
It's not all that difficult to install a correct D-type OD in a GT6, if you have all the proper parts. Quantumechanics sells turnkey-ready kits, and is a good vendor. D-types are not hard to find, really, and probably less than half the cost of a 5 speed conversion.

Properly maintained, a Laycock OD will last many tens of thousands of miles if maintained properly and not thrashed.

I installed a J-type in a GT6 and absolutely loved it. A D-type would have been just as good as I'm fairly easy on the car and don't race it.

Keeping the car period-correct is worth something, and also, the overdrive never fails to wow passengers when you shift in and out. Most moderns have never seen and OD, always a thrill.

Good luck, let us know . . . :thumbsup:
 
Will_Ringrose said:
Gliderman8 said:
I encounterd the same problem of high revs when traveling the highway in my TR6. I opted to make the conversion to a Toyota 5-speed. The conversion was straight forward and easy.
No leaks, and a dependable Toyota transmission.
Just a thought.
Click to expand...

What all is involved with that? Is there a kit I can get? I saw one for the ford type 9 transmission, is it the same idea?
Click to expand...

The conversions kits are pretty straight forward. The kits have an adaptable bell housing mating the new transmission with the Triumph engine. Once that is done (which is easy) it is just a matter of mateing it back up with the engine and re-installing in the car. I know I am giving you the short version, but really it is not hard.
For me, making the conversion is one of the best things I have done to my Triumph.
You need to evaluate your situation and finances and in the end make your own decision and it will be right for YOU.

edit: Bill does make a good point regarding your car. My experience is only with my TR6. If Bill says it won't work, he is giving you good advice.
 
I have explored the Toyota conversion into a GT-6 or Spitfire and have found it difficult because the Triumph frame interfers with where the tailshaft of the transmission would rest. The Ford Sierra 5 speed is also too long and is a weak transmission. Early Toyota W50 is too long, Datsun 210 might work but rare and hard to find. The Triumph frame is a problem, would require major surgery. Good Luck, Bill C. Mesa, Az.
 
It generally isn't cost effective to convert a non-OD box to OD, usually finding a factory OD is a better option.

For driving conditions out here anyway, and OD is almost essential if you'll be using the highways for any time period.
 
I converted a '72 Spit to an overdrive. I bought a parts car that had the OD tranny in it so I was able to use the rear mount,drive shaft and column switch. It is very simple to swap out the gearboxes.

I bought a D type OD tranny for my '69 GT6 from Quantum Mechanics for around $1300. Came with everything I needed to install it. The car is being restored from the ground up so I haven't been able to drive it yet, but I'm looking forward to it. I've done other business with them, and they can be trusted.

Also, as someone mentioned above, GT6's that came stock with an OD had the 3.89:1 final drive. I believe OD and a 3.27:1 diff was available in Europe for a time, but the gearing was widely considered to be too high.

I'm thinking about one of the 5 speed conversions for my TR4A, but haven't ruled out an original overdrive.
 
Since the XKE didn't want to be driven today, I got the 250 out. It was nice to flip the sw and drop the rpm's down. I second Skips words for Highway speeds. I have one in each car except the E.

Marv
 
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