Changed diff ratio - does speedo need re-cal?

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PeteE30Tourer
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Post Fri Jul 13, 2012 3:46 pm

Does the speedometer sensor on the diff pick up on the output shafts or the input?

I've just gone from a standard (3.73 I think) diff to a 3.64 LSD and my speedo appears to be reading much lower than before. Can it be re-adjusted?
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daimlerman
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Post Fri Jul 13, 2012 3:54 pm

Speedo sensor counts the output shaft,so swapping diffs will not affect the speedo reading.

3.64 will give 73mph at 3000rpm.

I have 3.64's on both of my E30's,one speedo shows 80mph at 3000rpm,other shows 77mph,but 73mph is the correct speed!
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PeteE30Tourer
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Post Fri Jul 13, 2012 4:36 pm

Thanks - I'll try to calibrate mine against my GPS, which should be accurate, right? Last time I checked, it was reading well high, but I guess it's better that way than reading too low.
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Brianmoooore
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Post Fri Jul 13, 2012 7:17 pm

PeteE30Tourer wrote: I guess it's better that way than reading too low.
The law insists on it!
A speedo. must not under read under any circumstances.