Here is my problem, i have a 91 firebird that was originally equipped with a 3.1 liter, auto 3:23 rear.

I took a 1987 305 tpi and auto trans and put it in my 91.

I kept my stock 3:23 rear end.

So basically its a 91 with an 87 motor and trans. The 87 had a 2:77 or 2:73 rear.

The trouble i am having is getting my speedo to be correct. Is that becuase of the 87 vss?

Do i need to change speedo gears or anything? I assume vss and rear end ratios are related. Do i just need a vss set for a 3:23 rear?

Any help would be great, thanks

 

You will need to get the correct speedo gears for your rear end and tire height.

 

I guess i am confused on why my speedo gears need to be changed. The speedo is from the 91, so is the rear. Sp the speedo sees a 3:23 rear, which is what it has.

 

All speedos are the same, they don't "see" any rear gears. They all want to see the same number of turns/mile of the cable, or pulses/mile of the VSS. The ratio of the speedometer gear converts turns of the rear wheels into the correct number of turns per mile.

If you didn't change out the gears in the transmission before you put it in, then you have speedo gears for a 2.73 rear. Change them.

 

Ah, now i see, thanks for your help