[Stokestack]

Hi all.

I recently noticed the speedometer on my '96 Cobra reading way too fast, but only once in a while. I doubted that everyone around me on the highway was doing 90, and sure enough my GPS said 73 while the speedo said 90.

But at other times, the speedometer is pretty much right on with the GPS.

Any idea where I should start looking for this problem?

Thanks!

 

[2Manystangs]

there's a little plastic cog on the transmission for the speedo cable, it's probably getting worn out

 

[Stokestack]

Thanks. I'm curious as to why this would cause it to read too fast, though.

I did some research on how speedometers work, and apparently there's a hairspring in there that opposes the movement of the needle (which is driven by electromagnetic force). If the thing reads too high, it seems that this spring must not be opposing the movement enough.

The mystery is why the problem is so intermittent.