Speedo

V8 Sam · Post by **V8 Sam** » Wed Jul 25, 12 10:04 pm

Hopefully in the correct part.

My 70 dart speedo is quiet out. Showing 60mph but my gps is doing 70+

Gets worse the higher up it goes.

Speedo cable had it or?..

Guy · Post by **Guy** » Wed Jul 25, 12 10:20 pm

Rear gears may have been changed from stock, possible axle swap, gearbox may have been changed and now has the wrong speedo drive or the tyres are not the right size(too tall), I dought its your cable unless its jumping all over the place.

Dart Vader · Post by **Dart Vader** » Wed Jul 25, 12 10:29 pm

gearing change most likely

V8 Sam · Post by **V8 Sam** » Wed Jul 25, 12 10:47 pm

Hmm, anyway to find out?

Post by **MattH** » Wed Jul 25, 12 11:07 pm

Fender tag might show original ratio and you can calculate your ratio now by marking the prop and tyre and turning one full wheel revolution and see how many turns of the prop you get. This will give you the ratio.

Car will need to be securely jacked up obviously, just on one side so one wheel doesn't turn.

Pete · Post by **Pete** » Wed Jul 25, 12 11:23 pm

You can put a different ratio speedo gear in the transmission. Also a big impact is tyre height - if the car came with little 14" tyres then swapping to big 15" tyres (for example) will make a difference.

There are resources on the web to calculate the correct ratio drive for your combo..........