1981 corvette speedo reading wrong speed

What vehicle are these rims for? Do you know what size rims and tyres should be on the vehicle. A wrong size tyre can knock out the accuracy of you speedometer. It will read as faster or slower than the speed you are actually travelling.

Have the road wheels or tyres been changed from the original manufacturer's specification? If they have been changed for larger (or smaller) diameter wheels this would necessarily alter the vehicle's speedo veracity! This seems the most likely cause of errors in speedo readings. If this is NOT the case, then it sounds like a speedo fault. Best of luck!

First car: 80km/hSecond: 60km/hI suppose....

on a car that old the speedo is most likely mechanical. there is a long cable in a jacket coming out of the end of the transmission which goes into the back of the speedometer. jack the car up and find and unscrew that cable. if it is broken buy a new one at a dealer or parts store. if it is not broken find an old transmission man and find out if there is a replaceable speedo drive gear in the transmission. if not you may be looking around for someone to fix that old speedo. google it i am sure there is someone out there willing to take your money.

remove your speedo cable if its in ok shape lubercate it with high temp greese if its not in good shape and it may not be replace it before it breaks off in housing

This is an electronic speedo, could be several things but probably 1st and easiest thing to try is repalceing the vehicle speed sensor(vss). Also need to know if check engine light is on, and if any other electrical items are malfunctioning.

unhook speedometer cable from transmission and spin cable by hand it should turn smoothly if it des hook end to a low sped drill and see if it holds at a steady speed if it does the the problem is in the plastic speedo gear in the trans if it dos not remove the dash and inspect the connection on the speedo head

I fixed it. You just need to physically move the speedo hand anticlockwise. Be careful though.

This happen to me too. Had to get it replaced under my exstended warrenty that cost me the $200 deductable but would of coast over $400 if this happened later.

Oh, i had this problem! you need to replace the clock i don't know the name but you need to replace the thing that shows you in which speed you are and the time and things.