For a stock 700R4 from a 1991 Camaro RS with an LO3, how many teeth were on the stock gear on the output shaft? What color was that gear? I'm asking because I just went from the stock 2.73 rear end gear to a 3.42 rear end gear and the speedometer is off. I know I have to change the gear attached to the VSS but I'm wondering if I can leave the gear on the output shaft as is.

 

Biggest problem you're going to have is that you will need a different VSS. When I went from 2.73 to 3.23, I had to purchase a different VSS that would handle a 45-tooth gear. The VSS that came in the car would not. You will have to swap out the drive gear, driven gear and the VSS to get your speedo reading correctly going to 3.42. Or you could use the Dakota Digital box to recalibrate.

 

YUP.

The 2.73 should have had a RED 17 tooth on the shaft and a BROWN 39 tooth on the VSS.

Assuming that your running 16" wheels; To get to 3.42 you're gonna' need a GREY 15 tooth on the shaft and a YELLOW 41 tooth on the replacement VSS.

 

I'm actually running 17" wheels with 245/45 tires.

 

Don't worry about all that. MEASURE the radius of the wheel/tire combo with the car sitting on level ground: pull a measuring tape from the center of the wheel to the ground. COMPARE to the same MEASUREMENT of some convenient one of the factory tire sizes, to the extent that the factory tire size is accurately represented by modern tires (which isn't as close as one might think). ADJUST your speedo gear choice by the percentage that your combo differs from the factory one. DO NOT attempt to "calculate" tire size using the wheel dia and the tire "trade" size; it won't be reliably right.

 

That's super close to stock 245/50R16.
John posted the GM documented gear combination for 3.42 above. Run with it.
Your VSS in the car is probably not the correct one for the higher tooth count driven gear.
See chart in this thread: https://www.thirdgen.org/forums/tran...k-drive-2.html
At this point, unbolt and pop the VSS out. Verify it's 17; usually red. Marker it and rotate the trans. in neutral and count if you must.
Order the 15t gear. And if your VSS has a 38 or 39 t gear, order the right VSS and 41t driven.