Driving home from work yesterday, my speedometer kept giving out. I was cruising along at 65, and the speedometer would show 0. I watched the arm flail about between 0-65 a few times, and it was freaking me out. The tach stayed constant and I was not losing speed.
This morning, on the way in, I did not notice anything peculiar. What happened last night?
Some GM vehicles will behave like that if you’re beginning to have a loose battery connection. I can’t say about other brands, but you might want to take a look at your battery terminals.
It’s a 96 Jetta.
The spedometer in my Nissan pick-up did/does that. The needle would bounce around between 0 and whatever speed I was going. These days it hardly bounces at all… just stays at or near 0. I never got around to having it fixed.
I think there’s a little set of cogs, maybe in the transmission, that spin the spedometer and odometer. (The tach is separate.) They’re probably made of plastic and the teeth on the cogs can get stripped. After a while the teeth wear down to where they don’t converge anymore and the spedometer and odometer both cut out.
This is my theory anyway. My odometer still says 135,000 and in truth there are probably more than 200,000 miles on the truck… which would matter if I planned on selling it some day, but I don’t. 
My GM 91 Pontiac Sunbird did exactly this, along with other electrical troubles, when water got into an electrical harness junction box. Electrical faults can affect your spedometer if it doesn’t rely on purely mechanical links to the transmission, but rather, and electrical signal. When you temporarily lose power, you also temporarily loose the carrier.
Hope this helps. Good luck.
Is it a mechanical speedo, or electronic? With the speed indicating zero, were you still continuing to run the odometer, or did that stop also?
My VW exposure ends circa SuperBeetle and 411, so maybe Gary T will swing by with an opinion.
Mechanical speedometer, with digital odo. Since it doesn’t register tenths, and since it was over a short distance that I noticed the funkiness, I’m not sure if the odo was impacted. I ran a few errands on lunch today, and nothing seemed out of the ordinary.
It was my mom’s car. Maybe this was just her way of getting me to slow down a little. 