TVR 3000M Ford Type 9 Gearbox speedo drive gear

[Gee Boo]

Hello all, following a recent gearbox oil leak and strip down, I have noticed that the speedo drive gear is badly worn and will need replacing. Along with first motion shaft, lay shaft, bearings etc
The question is, my car was always showing 10mph slower than when compared to the satnav.
Is now the time to change the speedo gear (assuming that the current blue one from whatever donor car is incorrect).
Any ideas of the difference the various colour drives make? Anyone have experience of what colour aligns with a TVR 3000M Essex V6 with the type 9 box, standard diff and wheels.
Appreciate that this will vary depending on diff ratio and tyre size etc,
Thanks in advance Gav

[Moto]

I'm no expert but surely if the speedo is as you say always reading 10mph slow them the fault could only be with the speedo unit itself All other possible faults would result in the speedo inaccuracy being a percentage of a true reading.

Moto

[Gee Boo]

Possibly, it’s just I suspect this gearing is from the doner vehicle .....

[Gee Boo]

This issue is moving forward quite quickly amongst my friends it seems I need the number of teeth on the shaft /number of teeth on the plastic gear drive /size of wheels and the diff ratio and there’s a calculation That reveals all ........??

[magpies]

Also be aware that it is illegal for a speedo to read less than the actual speed of the car.

[ATE399J]

magpies said:

Also be aware that it is illegal for a speedo to read less than the actual speed of the car.

Oops, mine reads about 25% slow!

[BIG DUNC]

I am not sure that is quite true. When new, to get. Type approval it cannot read under the actual speed.
Once it has that type approval....

[anonymous-user]

Had the OP considered an electronic Smiths Cobra Speedo?

[anonymous-user]

Gee Boo said:

Hello all, following a recent gearbox oil leak and strip down, I have noticed that the speedo drive gear is badly worn and will need replacing. Along with first motion shaft, lay shaft, bearings etc
The question is, my car was always showing 10mph slower than when compared to the satnav.
Is now the time to change the speedo gear (assuming that the current blue one from whatever donor car is incorrect).
Any ideas of the difference the various colour drives make? Anyone have experience of what colour aligns with a TVR 3000M Essex V6 with the type 9 box, standard diff and wheels.
Appreciate that this will vary depending on diff ratio and tyre size etc,
Thanks in advance Gav

There's a number of places in t'internet to find this out and an online calculator for the nearest match. I've just done this on the Vixen (driven gear change) and Tuscan (both gears). You're restricted to the available sizes of driven gear and driving gear and the Tuscan was right at the limit of both as the diff is 3.31 but you should be fine with the 3000M.