1956 chev speedometer

can someone tell me how to calibrate a speedometer on a 1956 chevrolet. I estimate its off 20 miles.I would like to do it my self.but don,t know how to go about it?I have put it in the vice and took a piece of cable with a drill to run it any advice other then send it out and pay $200.jerry geraldlinen@aol.com

gerald c linen

typically the speedometer is not off, it is usually the diameter of the tire, the rear axle ration or the gear in the transmission that is "off".

For instance if your speedometer is "off" 6 mph at 60 mph, your speedometer is "off" 10%. You will need to replace the gear that drives the speedometer cable with one with 10% fewer or more teeth depending on which way your speedo is "off" (fast or slow). In addition GM had stepping reducers that were available in a wide variety of percentages to correct the input to the speedo cable.

A simple change of tires can affect your speedo's accuracy if you change the diameter from what it was ...

Summary: it is USUALLY not the speedo ...

Jim Rohn

I know what your saying about the tires and the and the trannmission gear I should have said i had taken the speedometer out because it stop working.I thought the cable was bad but it was the speedomter head.I took it apart and put in a used odometer it now works but the speedometer is off 20 miles.