1991 Caprice Classic LTZ Digital Speedometer Problem

[ToyRoom]

I am the original/current owner a 1991 Caprice Classic LTZ.
Has over 125,000 miles and still love this car!

It has the "CERTIFIED" digital speedometer with the old fashioned "non-digital" odometer and trip odometer.
The speedometer just started displaying erratic speeds while driving.
The speeds are "all over the place" continuously, thus making the cruise control useless.
Also noticed that both odometers are not registering the mileage correctly.
A recent 100 mile trip only registered as 33 miles total!
This problem reminds me of a broken speedometer cable.
Is this it or is it something else??

Thanks in advance for any help!

[radioman2002]

One of two things has happened,. Either the wiring up to the dash from the transmission speed sensor is bad, or the speed sensor itself is going bad. Some times the plastic gear wears out or breaks, that could be the reason for the eratic readings. I would check the sensor first then chase the wiring problem, if it exists.