Sticking Speedometer

1998 Chevy Express van 5.7 auto. Last night the speedometer needle stuck at 65MPH. Pulled over turned the van off but the needle stayed at 65MPH. Drove a little more, then
the needle broke free and started to show the correct speed. But now its acts irractically, the needle gets stuck at different speeds before jumping aroud to the correct speed. No Check Engine light is on and the odometer works. Where should I start looking for the problem?
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There are traditionally two different types of speedometer drives. One is the mechanical drive which uses a cable from the transmission to turn a magnet inside a speedometer housing. The faster it turns, the more the speedometer head is displaced. If anything sticks due to dirt, a faulty speedometer cable, gears, etc, then you will observe the kind of behavior you have described. Fix...take it to a speedometer shop, if you can still find one. They can repair, calibrate, etc. OR take it to a dealership and they can replace it.
The other type of drive is digital, and an electrical signal is generated at the transmission sender. Eliminates the cable. The signal is converted at the speedometer to a display, whether it is an analog moving pointer type or LED display, or similar. The fix is the same.
It does not usually mean that there is anything wrong with your engine, or electrical system, or other.
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