I have an 88 IROC 383, 700R4 and I installed a 3.73 posi rearend. Drum brakes. I believe the vehicle came with a 3.07 rearend. Now the speedo reads like 100mph when doing 50mph. What can I do to corect this. The speedo is cable driven.

 

the speedometer gear in the tail end of the tranny needs to be changed to 1 with less teeth on it. i changed 1 before and its real easy...1 bolt i think and u have to pull it out...sometimes it gets stuck from being in there so long. u need to look up the biggest gear ratio for the same year car and see how many teeth would be on the gear for that size rear-end and go accordingly. they obviously never came w/ 3.73's so ull have to guesstimate.

 

I'm sure you can find aftermarket driven gears for almost any gear ratio if you look. Try searching www.jegs.com and www.summitracing.com for speedo gears. You should be able to find what you need and they're very easy to change.

 

Ok, thanks for the help, now I know what has to be replaced. Cant find speedo gears at jegs or summit. Has anyone ever put a 3.73 in camaro with stock tires. How many teeth were on driven and drive gear? Whats the formula? Where did you get parts from? Help!!

 

I got mine from GM. 15 tooth drive gear and 45 driven gear.

 

Try SLP, I think they have speedo. kits for a 3.73 conversion.