Gearbox speedo ratio

[Minishell]

Hi,

I'm the owner and on the final legs of a restoration of a 1964 mini 850 with a three synchro gearbox. Through my brief driving I've noticed the speedo reads faster than what the car is actually travelling (+10mph normally compared to my satnav).

I'm just having the gearbox overhauled and the garage has asked me what size / ratio spline needs to go on the end of the speedo cable immediately when it connects to the gearbox. Does this make sense to anyone and they know the answer?

I'd rather be clocking up actual mileage on the speedo rather than more that I'm doing on such a restored classic.

Many thanks all.

Steve.

[rich@minispares.com]

all older minis ran the same worm and drive 17/6 - the speedo head was matched to the final drive, so you need to look at the sn number on the face of the speedo and match it to the cwp.

the later cars ran a standard (in some respects) speedo head, and 'walked' the ratio by using different worms and drives.

[underkut]

I used a company called guessworks .
They have a very handy tool on their website that you enter in as many details as you can. From tyre size to speedo no and diff ratio or gearbox.
It then tells you your best match.
Mine turned out a couple of miles an hour out at mid speed but was pretty good low and high speeds and i put that down to the speedo itself.

[LarryLebel]

I consider only being out 10mph as highly accurate for a Smiths speedometer.

[dklawson]

John at Guess-Works will be able to help you after you have read through his online tech info on the subject. You will be most interested in the pages dealing with ratio calculation and TPM math.
http://www.guess-works.com/