Speedometer reads too fast and jumps - 1984 Chevrolet C1500

Wrong tires. wrong speedo on the transmission.

Find one of those radar displays that sit on the roadside and tell you how fast you're going. Most likely your GPS is the one that's off, because it has to average and estimate your speed, wheras the vehicle's speedometer should be good from the factory.

The speedometer cable needs to be oiled it is hanging inside of housing and when it comes loose it makes the speedometer jump up and down from cable hanging up inside of housing.

Good observation. Changing the tire size increases or decreases the number of wheel spins per mile, and that changes the speedometer reading. GM or a custom truck shop should be able to modify the speedometer drive, but most drivers just note the inaccuracy and learn to live with it.

Bill B

in fact it should read slow not fast with 10.5 r15 s on. if you go to any reputable instrument service they will be able to sort it out for you ,no hassles. "youdoit"

HI, the speed sensor is damaged. replacing the sensor will fix this issue.

there is no censor for speed on a buick skylark.
i have an 88 same motor and everything
u jumped a tooth on the gear that drives the needle.
u have to pop the dash off and get to the problem behind the main gauge and the needle assembley should come right out. either that or you stripped the gear and its just going wherever it pleases.

try looking at the book theres a cable from the transmit ion to the speedometer and it could be a bad connection or theres a gear in you're trans that spins and tells how fast you're going sometime those go out haven't had that problem yet but i built my truck from the ground up

speedometer cable? speed sensor or speedometer meter it's self! engine light on scan obd 2 to retreve codes don't gue$$

bad speed senor on trans