spedometer help

[DrSanchez]

I am having trouble diagnosing the problems with the spedometer. It reads 40 mph at 25 and reads about 80 at 70, so the faster i go the more accurate it is. In addition the needle bounces back and forth no more than 5 mph while driving. Is is the whole spedometer or the cable or what???

[TcmaBoy]

Could be the speed, could be the cable. Only one way to find out.

[projectsupramk3]

How are you calibrating the speedo and getting these speeds to compare? With a radar gun? Is everything original/stock, wheels, transmission, differential gear, speedometer?
The bouncing needle means one of your two speedometer cables is about to break, filling the cables with oil could solve the problem, but they could also be too far gone to fix.

[DrSanchez]

My tranny just took a dump and from what i hear that will mess up your speedometer. Thanks for the help.

[projectsupramk3]

No it will not, that would only cause the speedometer will stop working when you're transmission stops turning. There are a number of other problems that could have contributed to you're calibration issue over a year ago.