View Full Version : Overdrive Conversion

02-06-2007, 07:05 PM
Hey, this may seem like a dumb question, but I was wondering if it is possible to convert a non-overdrive engine to an overdrive... and if it is possible, the pros/cons of such a conversion like the cost, difficulty, and benefits... I have a 1970 spitfire with the engine from a '78 spitfire 1500



02-06-2007, 07:10 PM
Its the transmission that is converted. It can be pricey unless you have a line on a overdrive tranny allready. Lower revs makes highway cruising very nice. Good for the resale value but as i mentioned before, unless you have an overdrive tranny ( or an overdrive mainshaft to convert your exsisting gearbox ) it tends to get expensive........

02-06-2007, 07:38 PM
Alex Check the archives .There is probably enough info on this to fill the Library of Congress.

02-07-2007, 09:14 AM
Yes it is possible. I did it with my MkI. I little harder because it was a 1500 OD unit and not the correct one for an 1147. It adds more weight and, as stated, can be pricy. I bought a no-title parts car that had the OD (thats why I bought it) for $250. It works fine so I got a pretty good deal. You will need the correct drive shaft and rear trans mount plate and rubber mount. I got all these from my parts cars.

The conversion helps immensely at cruising speeds and the resale value of the car. I also went with a 3.89:1 diff and am in the process of getting a 3.63:1 diff rebuilt. Then I ca really cruise with the big boys (if the engine will pull this load).

02-07-2007, 10:58 AM
An O/D is really nice to have, it make a Spit a much more capable touring car especially if there is highway work that is part of the mix.

As mentioned above, looking for a parts car with a complete set can be a much cheaper way to go if you can find one.

Here is a link to a shop that is well known and well regarded.


02-07-2007, 11:59 AM
I haven't converted a car to overdrive, but I have put a non-overdrive engine in an overdrive car and noticed a few differences.
The clutch is a completely different diameter(in my case the car was late model), you will need a flywheel and clutch to match the overdrive transmission. You are probably on your own for wiring, you may have to make your own small harness/wires. The drive shaft is a different length, and the trans mount is different.
Sounds like a lot, but it all comes together quite easily if you have the parts. Plus, if you are really anxious to drive, you can do it in stages, like refurbish the trans, and install. Then hook up the wiring when you have time.

Adam H.
__________________________________________________ ____________________________
1973 Triumph Spitfire

02-08-2007, 09:08 AM
My son And I did the switch in a TR6 with an overdrive tranny out of a rustbucket car and it really makes it a better car. The key is the patience and desire to find an overdrive in a dead car, its less expensive.