Speedometer/odometer correction

[Dobreutra]

Hi,
I have a 23 t-bucket, 350 chevy engine, 2 speed powerglide transmission, and 8" Ford rear end with Mickey Thompson 31X16.50-15LT tires. I need help correcting the speed and odometer readings. I was driving at what indicated on my speedometer 40mph, a friend was following me and said I was actually going about 60mph. I drove on the interstate today and went 5 miles indicated by mile markers...my odometer indicated I had travelled ~4.1 miles. Is there anything on the market I should buy and install that will correct the readings? The speedometer/odometer is a Stewart Warner 824263. I look forward to any suggestions.
ps. I've had my 1st bucket for 6 weeks now, and I'm still trying to figure out why I've waited so long to own one. Mid life crisis possibly?
Harry

 

[Mike]

Is your speedometer using a mechanical cable or an electric sending unit?

The mechanical units are calibrated to read 60 MPH at 1000 RPM. You would calibrate this to your combination with the use of a different drive pinion. The pinions are available from S/W.

If the speedometer is using an electrical sender, then you can calibrate the unit yourself, by simply driving a precisely measured mile. See here for directions on how this is done.

 

[blownt]

You can go to a speedometer shop and they can make you an adapter that screws in either at the speedo or trans. They need to know what your drive gear and driven gear in the trans, tire diameter, rear gear, etc... and they will make you an adapter. It just spins the cable faster or slower depending on what ya got.


http://www.speedometershop.com/ratio.html