6 replies to this topic

[bantu]

Hi,
I'm having trouble working out the correct worm and pinion for my centre speedo.
TPM of speedo is ‪1280 - 90‬mph smiths central pre 84
Tyre size - 165/70 x10
Engine is a ‪1988 1275‬ mg metro which I'm guessing has standard gearbox for that engine.
In the ratio calculator on guesswork website it's suggesting 6/17. That ratio is already in and the speedometer is reading over, for example travelling at 50mph and the speedometer is reading 70+.
Any help would be greatly appreciated

[DeadSquare]

Hi,
I'm having trouble working out the correct worm and pinion for my centre speedo.
TPM of speedo is ‪1280 - 90‬mph smiths central pre 84
Tyre size - 165/70 x10
Engine is a ‪1988 1275‬ mg metro which I'm guessing has standard gearbox for that engine.
In the ratio calculator on guesswork website it's suggesting 6/17. That ratio is already in and the speedometer is reading over, for example travelling at 50mph and the speedometer is reading 70+.
Any help would be greatly appreciated

50 to 70+ is a hell of a lot for a gearing discrepancy.  Are you sure that you haven't got a KPH instead of MPH speedo ?

[bantu]

It's mph speedo

[Spider]

If your numbers are right, then you need a 2.02:1 ratio speedo drive, which just isn't available. The closest you'll get is 2.14:1 with a 7 tooth worm and 15 tooth pinion.

However, there's got to be an error in your assumptions as to what you have in your car now, or your speedo is way out of calibration.

To check the speedo, forget the indicated speed, look and note down the odometer. Drive a known distance (the further the more accurate) and see how far it has indicated. Then from that, we'll know what your speedo should be saying, that'll help steer us from there.

[bantu]

If your numbers are right, then you need a 2.02:1 ratio speedo drive, which just isn't available. The closest you'll get is 2.14:1 with a 7 tooth worm and 15 tooth pinion.

However, there's got to be an error in your assumptions as to what you have in your car now, or your speedo is way out of calibration.

To check the speedo, forget the indicated speed, look and note down the odometer. Drive a known distance (the further the more accurate) and see how far it has indicated. Then from that, we'll know what your speedo should be saying, that'll help steer us from there.

[bantu]

It's a 1988 mg metro engine and gear box so what would the FD ratio be? 3.444:1?

[Spider]

It's a 1988 mg metro engine and gear box so what would the FD ratio be? 3.444:1?

 

If original, yes.