I have a 1981 VW pickup with the 5 speed tranny and the 1.6 diesel. The truck has 14" wheels from an audi 4000 on the truck instead of the factory 13" wheels. The odometer is very inacurate, and I know of the fix on the spline with super glue, however the speedo is way off too. At an indicated 55mph I am doing about 75mph. Is there an adjustment potentiometer to compensate for the other wheel size? I wouldn't think 1" would make 20mph in difference. Thanks for the help.