Innacurate reading with 1971 corvette speedometer

Corvette 1997-2005

Vehicle Speed Sensor

The VSS is located on the rear differential case.Here's a picture of a new sensor Sam.
Vehicle Transmission Speed Sensor at AutoZone com Best Vehicle...

The speedometer can fluctuate rapidly under normal driving conditions when the car's speed changes abruptly, but sometimes the needle can start swinging around the dial without any fluctuation in speed. If the hairspring comes loose or breaks, it can't hold the speed cup in place, and the result is a fluctuation in the dial. In electrical speedometers, if the circuit that counts the magnetic pulses fails, it can cause the speedometer read-out to vary from the actual speed and to shoot upward or downward without notice. If a speed sensor in the automatic transmission starts to malfunction, it can affect the speedometer and cause fluctuations. In these instances, either the speedometer or the sensor needs replacement.

Do you have a fuse for "gauges" and does it have power ?

Turns out this is a common problem for the Rendezvous.
I took it to a mechanic and after he tested to see if all the speed sensors were working with his handheld computer reader, (because there is no speedometer cable anymore) He reset the needle by turning the key about 25 times as far as possible without starting the vehicle. The speedometer needle came back a bit each key turn till it reached zero. It's been working fine since.

The speed senser is mounted on the transmission. This device is an slocrto magnatic motor and they cost less than $100 there held in with one bolt and have an electrical connector. Many times if it's bad enough the check engine light will come on. This problem but the heating up but work OK cild is a good chance the senser has failed.. The trans mission should be checked for overheating as the senser failure will be heal related

Its a loose connection on the speedo cable. its a b*tch to get to. I had the same problem on my truck, it would fluctuate in 5th gear on the highway. i spent the money and had a professional do it.

u may need a speedometer signal generator if dash gage is on just not reading speed its located on the left rearend of tranny just remove wiring clip and 1 hold down bolt and pull out easy to replace but if its problem with dash gauge's u may need a dash printed circuit board for speedo/tach

IMHO, I think that the broken cable is what is causing the problems. It "confuses" the programing of the CPU or computer.

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

Is it the 5.7 L? It's mounted on the transmission. countrycurt0