speedometer function - Accuracy - The 1947 - Present Chevrolet & GMC Truck Message Board Network

RyansToy · 12-09-2015, 04:18 PM

So I took my 68 out for a longer trip before I put it away for the winter. My buddy followed me to the storage spot (~250 Miles).

I have never checked the accuracy of the speedometer with GPS or a friends vehicle till now.

Odd thing was that at 50 MPH the speed appeared accurate,
But at 60 or 70 MPH the speedometer is ~30% low.

How does the speedometer work? does the mechanical cable turn a friction mechanism to show the speed? or does it turn a small generator to move an electrical gauge?

I would have thought the speedometer would be either correct, or wrong, but not both....

12-09-2015, 04:18 PM	#1
RyansToy Registered User Join Date: Aug 2015 Location: Nova Scotia Canada Posts: 145	speedometer function - Accuracy So I took my 68 out for a longer trip before I put it away for the winter. My buddy followed me to the storage spot (~250 Miles). I have never checked the accuracy of the speedometer with GPS or a friends vehicle till now. Odd thing was that at 50 MPH the speed appeared accurate, But at 60 or 70 MPH the speedometer is ~30% low. How does the speedometer work? does the mechanical cable turn a friction mechanism to show the speed? or does it turn a small generator to move an electrical gauge? I would have thought the speedometer would be either correct, or wrong, but not both.... __________________ 1968 GMC truck 910 Trim (Canadian) 127" WB 3 on the Three Trans (Saginaw SM330) 250 ci L6 Engine HEI ignition (early 80s L6)



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