Topic: 1979 firebird speedometer

[79 Rebel]

i have had my firebird for 5 years now ever since i got it my speedometer has been 5 miles off and past 40 about 10 miles off
it also starts to jump and shake past 45.
somebody told me to oil the cable my question is how to i take the dash apart by the gauges and do you guys think this is the problem
thanks

[ta78w72]

No, oiling the cable won't help.  Are you using a standard tire?  You may have to change the ratio gear at the transmission.

[79 Rebel]

no i do have bigger tires on the back
and smaller tires on the front
how would i  go about changing the ratio

[Hitman]

The spedometer jumping and shaking is usually due to a cable starting to go bad or needs lubricated.  The speedometer being off does have to do with the different size tires.  If you take your original tire size and what it was supposed to be and your new tire size and do a little math, yu can figure out how far off you are.  Changing the rear end will get you off probably even further.  You can play around with the speedoemeter and drive gears in the transmission to get your speedometer a little closer to accurate.  It is relatively inexpensive and fairly easy to do.