I have a 1985 iroc witha 3.73 rear end (which is not the origonal). When I am going about 65mph the speedometer says I am going 100mph. I have tried many different speedo gear combinations but cannot seem to get the right one. If anyone has a 3.75 rear end, and knows the speedo gears that they have please let me know. I am racking up miles like crazy.

 

We've got to be reaching the hundred mark on this question. I'd be glad to answer but just like the other 99 times no information is provided. Sorry...Go to the top of the screen here, hit the search button and type in speedo gears.

 

Well said, Jay.

 

What tranny you have?

 

I have the 700r4, so thats a .70 final drive.

 

What is your rear tire height in inches................................

 

Well my rear tire height is 26", but I just thought of something. I know that I have a 3.73 rear end, because I have done the spin the tire test and all the math stuff. and I was reading other peoples posts and saw that they used 15t and 45 t gears. those are the gears that I currently have and the speed is still wrong, so I was wondering if it is the speedometer's fault(since it is not the original, I think its from an 84). Are different speedometers calibrated differently.

 

You have the correct speedo gears. Change out the speedo itself to verify. A junkyard will sell you one cheap.

 

Hey, Thanks a lot guys. I will try the different speedometer and see what I get.