speedometer fluctuation

While driving, if I hit a large bump in the road, my speedometer goes to zero. If I hit another bump or hit the top of the dashboard, it starts working again. How do I access the speedometer cable and assembly behind the instrument panel? Also, what else could be loose? I looked from underneath, but can't see anything. It drives me nuts. Thanks for the help.

While driving, if I hit a large bump in the road, my speedometer goes to zero. If I hit another bump or hit the top of the dashboard, it starts working again. How do I access the speedometer cable and assembly behind the instrument panel? Also, what else could be loose? I looked from underneath, but can't see anything. It drives me nuts. Thanks for the help.

I currently have the same problem with my 1991 Century. I will be driving and hit a bump and all of a suden my check engine light comes on and my speedometer reads 0 mph. When that happens, the car will sometimes die when I am at a stop light. I have to give it some gas while I apply the brake. Then all of a sudden when I am driving again, everything will be normal. Anyone out there who can help us out would be appreciated. Thank you.