A word of clarification might be in order here. Until sometime in the
1970's, the TR series of cars all used the same speedo drive pinion gear
in the transmission. Differences in final drive ratio and tire size
were accomodated by different speedometer heads. So, a 4.1 TR4A had
exactly the same pinion as a 3.7, only the speedo head changed.
There is a 4-digit calibration number (in cable turns/mile) printed on
the face that distinguishes, it's typically around 1180 for 3.7 gears,
and 1350 for 4.1 gears. Sometime mid-TR6 production, that changed, and
later TR6 all used a speedo head calibrated to 1000 turns/mile; with the
drive pinion altered to suit tires/ratios. I'm not sure how, or if,
this applies to other S-T cars (or TR7/8).
Randall
Graham Stretch wrote:
>
> Hi Gerald
> I don't know about your car, but a lot of the Triumph range use a similar
> gear box, and if you have OD you laughing, as all you need to do is find the
> correct parts for the car that originally used that rear ratio, the early
> 2000 MKI saloons for instance had the 4.1:1 axle, also you could just count
> the teeth on the speedo pinion gear and work out the ratio of turns to the
> prop shaft, then reverse the maths to find the number of teeth you need on
> the pinion for the axle you have. This is what I did when I put the 3.45:1
> diff in my saloon, replacing a 4.1:1. I phoned ORS and they were able to
> provide the right ratio bit for the application.
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