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'71 140 speedometer ratios/turns per mile

vwbusman66

vwbusman66

Stößelstange über alles
Joined
Oct 12, 2016
Location
SE MI
So, I'm getting ready to try and figure out what gears I need for my T5 swap in my formerly M40 142S. It has a 4.10 rear end.

What RPM does the speedometer want at 60mph, or how many rotations does it want per mile?
 
If you still have all the components that came with your 140 that is easy to figure out. Check the ratio of the M40 output shaft to the speedometer drive gear. You are going to need that same ratio for the T5. Knowing that ration and your rear end gearing and tire size you can figure out how many revolutions per mile. This is all simple math. Something you should do yourself as an exercise in learning to build custom installations.
 
2manyturbos said:
If you still have all the components that came with your 140 that is easy to figure out. Check the ratio of the M40 output shaft to the speedometer drive gear. You are going to need that same ratio for the T5. Knowing that ration and your rear end gearing and tire size you can figure out how many revolutions per mile. This is all simple math. Something you should do yourself as an exercise in learning to build custom installations.
Click to expand...

I'd do that if I had the M40 here with me where the car is.
Sadly, it's 3.5 hours at home.
The math isn't the issue, it's knowing what the speedometer head wants to see.
 
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