I need to know how I would go about fixing my speedometer problem. It is about 10 MPH off. When Im driving, if im going 40 MPH, IM really doing 50. So what caused this problem? I think its connected to the tranny gears isn't? Please help. I dont know if I need to replace the speedometer cable or what. Thanks.

 

86 Trans Am, 4bbl, 305 ci, True Dual Exhaust.

 

What does it read when you are completely stopped?? 10 or zero?

 

Closer calibration can be done by changing the VSS drive or speedometer cable drive gear. What rear gear ratio are you using?

 

If you have ten cover bolts in the rear cover for the axle, you have a Saginaw 10-bolt axle. If you have nine bolts in teh rear cover and a rubber fill/inspection plug about 1/3 the way up the cover, you have a Borg-Warner axle. Either one could have disc or frum brakes. Either one could be a clutch-type positraction differential, but a non-posi Borg axle is rare.

With a Saginaw axle, there is usually a metal tag held in place by one of the upper cover bolts. The axle code information is stamped into this tag.

With the Borg-Warner axle, the axle code is stamped on the front side of the right (passenger) side axle tube.

Aside from that, you can remove the cover and count gear teeth, or you can place a chalk mark on the tire and one on the driveshaft, turn the driveshaft until the tire makes one revolution, and count the number of turns made by the driveshaft.

Any of those methods can reveal the rear gear ratio. Once you know that, you'll have to remove the speedometer cable driven unit from the transmission and count the number of gear teeth on the plastic gear. The color of the plastic gear can also be significant. The correct replacemetn gear can be puprchased at the dealership.

 

warrior, in your email you told me that at a stop your speedo is at zero. Your speedometer is probably calibrated okay. Like vader is saying, you probably need to change the speedo gear in your tranny.