It will affect the speedometer but the tachometer will still be accurate.
rpm and speedometer gauges not working 1995 Chevy silverado 2wd
If the speedometer is not working but the odometer is, I would suspect the dash cluster is at fault. If both speedometer and odometer are not working I would suspect the speed sensor on the transmission is at fault.
If the speedometer is not working it probably needs a new speedometer cable. If the speedometer is actually broken either take it to as speedometer repair shop or replace it.
Instrument Cluster has been recalled take it in to your nearest Chevy dealership
It died of Chevy Envy
If both the speedometer and odometer stopped working it is probably the speed sensor in the transmission gone bad. If only the speedometer quit you may have to replace the dash cluster with a reconditioned unit.
There is a problem in the cluster. I would obtain a good used gauge cluster from a salvage yard , they are easy to replace. The only tools you need are a Phillips screwdriver, and a 7mm socket and ratchet. Once the dash plastic is off the unit just plugs in. But of course, check your fuses first right?
There are several possibilities why the speedometer is not working. The VSS, vehicle speed sensor may have failed or become unplugged. The speedometer may have failed, or the ECM, engine control module, may have failed or there could also be wiring issues.
Someone knocked a wire loose.
The dealer has to program it.