I have recently put a speedometer from a formula 350 firebird (3.27 gears) into my firebird (2.77 gears). The speedometer is completely wrong (way faster than I am really going). The odometer has completely quit.. I have the whole rear out of the formula with the 3.27 posi that I am going to put into my car. I want to know if the speedometer will stabilize with the other rear, and what to do about my odometer. I have heard that the electronic gauges sometimes have shorts and can be fixed if you know what your doing.. Someone please give me an answer.
Thanks,
Wes

 

If your speedo gears are for a 3.27 rear end ratio, then yes they will be correct when you put in a 3.27 rear end.
I have no idea about your odometer.

 

did you change the whole cluster or just the speedo head? Were the two identical, 85mph,120mph, etc?

As far as the odometer not working I have three of them that dont work. One day I may look to see if I can repair them.

 

I changed the whole cluster a 120mph to 140mph.. Just the odometer doesn't work.. I'd like to know how to repair it.

 

I'm not sure why the odometer quit working but changing the rear end won't help with the speedo being off has Kevin91Z may have suggested. These speedometers are electronic so you would have had to change the gearing on the input shaft of the transmission in order to make the speedo incorrect. Chances are the reason you aren't getting a correct reading is because the gauge is bad, as evident by the odometer not working. Gauges can also lose proper calibration over time so that's a possibility as well.

 

Ok.. Stock, my car came with 3.08s and the 120mph worked fine. I swiched rears with one that had 2.77s because mine had bad bearings.. after that the speedo was like 5 miles incorrect. The 140mph speedo shows 80 when Im going 65 (according to a friend infront of me on the highway) So I guess the theory now is that its way off calibration and i need to take it to someone because I can't do anything to fix it?

 

To fix a speedometer reading incorrectly after a rear end gear change, you need to change the speedo gears in the transmission.

 

i heard that there are different speedometers for autos and sticks there nunbers i think on the dash cluster.

 

Nah.

JamesC