Speedometer on a 1991 chevy silverado reads 80 when only going 35-40.

you need the correct sensor
seem to be an incompatibility between the gearbox and the computer

is this a problem if oil pressure is 80 when i start it up?

Hi Norton,

What has happened is your speedometer and tachometer drive motors are failing inside your silverado instrument cluster. I see this very often in GM trucks, to fix the problem you need to have your instrument cluster rebuilt.

Check out this article that talks more about it http://drspeedometer.com/chevy-silverado-instrument-clusters-why-they-quite-working

Thanks,
Fred

The stepping motors in the gauge go bad, but uusually they fail gradually, or just one, The dealer charges $300 to fix, do a search on ebay for CHEVY SILVERADO INSTRUMENT CLUSTER for cheaper repair options. gauges are powered by the pcm, no fuses inbetween, so if it runs ok, problem is in cluster

speedometer is electronically driven usual cause is coil in spedo itself u would have to replace , pull panel and test voltage if power bad spedo, info on how to do chiltons book at most any parts store

replace instrument panel cluster

There is a recall on the dash cluster for your truck. Check with dealer but don't let them give you the run around.

The stepping motors in the gauges go bad. do a search on ebay for CHEVY SILVERADO INSTRUMENT CLUSTER for cheaper repair options. The dealer charges around $300.00. It will continue to worsen.

What year is it? I know on the older models that the cable went right in to the top of the tranny and the gear was plastic and would wear down and not work or the cable would get pinched.

needs new cluster check with dealer might have recall