I've got an '85 Trans am that has a T5 tranny and I swapped the 9bolt BW out that had 3.27 gears with a moser 12bolt that now has 3.73's. I read the stickys about the speedo gears and so forth, and figured out i actually need a 20 tooth driven gear with the 3.73 gear ratio and the current tire size I'm running now. My question is do I have a mechanical or electronic speedo? The parts guy at the dealer said i need a 140..... something part number, but I was thinking it was the number 3987920??

 

Welcome to TGO, 07rattleleak.

IIRC, 82-85 were mechanical. A quick look will verify.

JamesC

 

That's what I was thinking it being mechanical. I'm confused as to which driven gear it actually needs. Do I need the gear with the plastic shaft or the one with the metal shaft? How do I know which one? Correct me if I'm wrong, but is the 3.......series part number the plastic shaft and the 14......series number the metal shaft?

 

The 20 and 21 tooth gears with metal shaft are discontinued, so plastic it is.

 

That's kinda what I was thinking. So are the two interchangeable then? Just one has a metal shaft and one a plastic? Or do I have to modify the plastic one to fit?

 

Do your rear tires stick out further than stock, now that you have a 12 bolt. ?

 

No they don't, overall width is still the same as before.

 

Basically yeah.

Your old speedo gear sleeve might work fine w/ the new gear.

New ones are steel and have a seal that may need pressed inwards to meet the sealing surface on the new gear.