OT: Street Rod Speedometer

http://www.transmissionsone.com/speedometer_gear.htm

I just put a different one on my truck to because it was off by 9%. You can calculate exactly what you need - and the little gearbox hooks between your trans speedo cable.

Many places sell them - one is:
http://www.transmissioncenter.net/727Transmission.htm

If it is a mechanical speedometer, you can change the speedometer drive gear(s) in the transmission, or there are speedometer drive adapter gearboxes with different available gear ratios to correct the error.

If it is an electronic speedometer, there are electronic units available to make the correction (DRAC's)

I changed my F-150 from 3.08 to 4.10 gears. It had an 18 tooth driven gear, and I computed I needed a 24 tooth driven gear for the same driver. I had to go to a couple dealers who customized Mustangs to find a 23 tooth driven gear (6 months later truck and it would have been a computer setting). Since the teeth on that gear are very thin, I bought a spare. So far in 80,000 miles I've not needed the spare.

It should be that hot rod shops that sell rear axle gears carried the speedometer gears, but I've not found that to be the case.

Gerald J.

Knowing that, GOOGLE speedometer gears (make).

Link