Vitesse overdrive conversion

[TR7th Heaven]

Hi All,
My Dad is presently renovating a 1970 MKII Vitesse convertible.
The car is non-overdrive but he has the opportunity of buying & fitting a known overdrive gearbox and ancillaries.
My question is - Does he need to change the diff as well?
I believe that the diff has a 3.89 ratio (from info on here). Was it the same regardless of whether overdrive was fitted?
Any help would be appreciated.
Cheers
Richard

[malcty]

Richard. I had my 1970 vitesse converted to overdrive about 12 months ago. Best item done to the car. Thoroughly recommend it. I have kept the original diff, and car still drives well. However I understand there are three different ratios and sure you will receive more advice on these. As my diff is now wearing and growling it will be time to consider an alternative ratio. I think it depends on whether you want acceleration or higher speed. Good luck to the conversion. Malc.

[Richard B]

Standard 2Litre Vitesse's had the same ratio 3.89 as the O/D Vitesse's.

It will just make it nicer to drive. 3.63 (1500 Spitfire) is an option, as is changing the final drive by fitting different wheels & tyres.

[TR7th Heaven]

Thanks to both of you.
It's good to know that my Dad won't need to make any immediate changes to the diff. Assuming it's a good diff that is, it hasn't been tested yet! If it isn't and he has to replace it, he could consider the 3.63 for easier cruising.
He'll be running it on standard wheels with slightly fatter tyres (brand new tyres from a different abandoned Ford project).
So if the diff is correct then the speedo should be correct, regardless of having overdrive.
It's all good , as they say.
Thanks again
Richard (wink)