Having some issues with my 1991 Mazda 626. The speedometer seems to have a mind of it's own. I was running down the interstate today and it started to jump around slightly, and then it just pegged itself and made some high RPM grinding noises. It did this for awhile and then went back to looking normal, except it was around 20-30mph faster than I was actually going and jumping around 5-10 mph. Then it would go back to being pegged. It did this multiple times on the way home today. I checked the gear in the transmission, it was fine. Before I go tearing into the thing, I kind of wanted some more opinions on what it would be?
Thanks in advance!