I just got a 9 bolt rear end from a ws6 89 transam. When i opened up the rear cover, i counted up the teeth and i get 38 and 10. Does that mean its a 3.8 ratio? The guy i bought it from said its a 3.45, but he never run it in his car. Also, when i opened up the cover, it didn't have the original gasket and there was a lot of weld spots and scratch marks on the diff. cover, which probably means someone grenaded this rear end already and most likely put different gears in it - the 3.8's? The gears themselves look in excellent shape.

I also counted # of revolutions the driveshaft turns by the time the wheel turns fully once, and i got about 3 3/4 turns.

3.8's would be nice,

 

I would suspect you miscounted.... AFAIK there is no 3.80 ratio in those.

38/11=3.454545454545

 

Count the teeth again. There is some odd ball stuff around, but 3.80 would be news to me. All the 9 bolt ratios (factory and other) are listed at www.9bolt.com

Miles
Diff Solutions
www.9bolt.com

 

I guess i did miscount them, this time i got it right for sure.
37 and 10.
there is also this code stamped on the bigger gear:
G01-878370BW 37-10 U.S.A. C7

I'm guessing i have 3.73's then?

thanks

 

3.70 (37/10=3.70)

Typically came in 85 TAs with L69

Didn't come from the factory in any 89 car AFAIK, of course that doesn't mean it didn't come out of one

 

878370bw is us gear's pn for 3.70 gears, so somebody replaced the original 3 series gears with that set.