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Speedo Wrong :(.

Started by Hewlett_T , Dec 07 2016 04:35 PM

Best Answer AndrewT , 09 December 2016 - 10:07 PM

Thanks for the reply.

I understand the dividing by 2 bit now however I still think you have the fractional bit wrong.

You need to do 35 / 64.75 = 0.54. That makes 5.54 total turns which if you then divide by 2 gives 2.77.
Then divide 10 engine turns by that to get your ratio gives 3.61:1 which is close enough to the metro size of 3.64 that you first thought it was to be due to a small measurement difference on your fractional turn. (32 rather than 35 would give exactly 3.64)

The other way of looking at it is that the way you have done it your fractional turn works out as more than a single turn which can't be right.

Hope this helps you find the speedo drive bits that you need.

Edit: A quick back calc on the worm and pinions listed on the guessworks shows that 7/18 is almost bang on for your over-reads. 5/18 will give you what you need. Go to the full post