How often was the 3.70 9-bolt used in the Trans Am's? I just picked one up at a junkyard from an '85 that was a 5-speed/LB9 (verified by the F in the VIN) car, 9 bolt still has the tag on the rear and when I ran the S/N it comes back as a 3.70 posi rear.

Was this an unusual option on these cars?

 

don't think the 9 bolt was used untill 87

 

A very limited number of cars got a 9 bolt in 1986 but chances are you'll never find one that did. 1987 the 9 bolt became the performace option. The 3.70 gears were never a factory installed option. They were only available as an over the counter item from GM.

 

So I can assume that this was a good find? I went back out and looked at the tag again, it says Ratio 3.70:1 and the part number (10032274) and the serial number which I can't make out. The 10032274 shows as an '85-'86 Borg Warner part number where in '87 the 3.70 wasn't offered and the part numbers went from like mine 10032274 to 4ET, 4EW etc etc.