hey guys as some of you know who have helped me out earlier, i am about to pick up my new rear from an 87 formula. now the guy who i am buying the rear from is telling me that the gears are 3.73's, and that he never has changed them. I didnt think that 3.73's ever came in the rears from the factory. The rear has disc brakes and it is posi it is also a 9 bolt. Do any of you know most likely what the gear ratio is? i am thinking most likely it is a 3.45 ratio. Did 2.73's ever come in formulas with posi, disks, and a 9 bolt? i am praying that they didnt. thank you guys for any help.

 

The LG4 (carbed 305) Formula's in 87 came with 2.73's if an automatic, and 3.23's if a 5 speed. If it's TPI and auto, then it's a 2.73 rear and if it's a 5 speed, then it's a 3.23 or a 3.08. SOME had Borg Warner axle that had either a 3.45 or 3.27 ratio.

 

BTW, in case he's wrong about the year, some 86's came w/ 3.73's.

 

you just reminded me of something, i thought that the last year for 9 bolts was 86. And this rear is supposedly an 87. hmmm somethings not right here, or am i wrong about the 9 bolts stopped production in 86.

 

I've got an 87 formy with a 9 bolt, 3.2X's (never can remember if it's 23's or 27's; one is the ten bolt equivilent and one's the 9bolt) and an auto tranny. I'm in the process of swapping almost all that out but the car was completly stock beforehand. I know it came from the factory like that, my parents are the original owners. I've mostly seen 3.2X 9 bolts though...

 

I thought 10 bolts started in 91.

 

I believe you are right about this now, i was just doing some more research and found out that 9 bolts were made past 1986. Thank you guys for everything you are helping with!!

-Ian

 

If you look in the Haynes manual it lists every rear end for every year and shows which years had the what.

If you look on the housing, the factory tag bolted to one of the cover bolts tells you the gear ratio. If the tag is missing, unbolt the housing cover and look on the gear. The BW units have the gear ratio stamped right onto the gear ... listed as BW 2.77, BW 3.08, BW 3.27, BW 3.45, and BW 3.70.

As you may have noticed I put 3.70 not 3.73 as well as 2.77 and not 2.73.... the factory 9 bolts were never manufactured with 3.73 or 2.73 gears, only 3.70s and 2.77s. You can buy aftermarket 3.73 gears for the 9 bolt but if this guy is saying it's factory, then it's not 3.73s. It's not 2.73s either because the BW units were 2.77 gears. I think this guy has no clue what he's talking about or he's lying and has actually changed the gears.

 

7½" 10-bolts in these cars have been there all along, since 1982, and continued through 2002.

9-bolts were used in some cars from 85 to 89.

A 87 Formula could have either a 9- or 10-bolt. In no case would it have come with 3.73 gears; that ratio wasn't available in 9-bolts at all, and were a very rare special order only item in 10-bolts. At best it would have a 3.45, and even that's unlikely; most likely it's a 2.73, 3.08 or 3.23 if it's a 10-bolt, or a 2.77 or 3.27 if it's a 9-bolt.

Like I told you in the other post, the odds are heavily (like 10,000 to 1 or higher) that the guy is either guessing, misinformed, or is just outright lying. Screw the "codes" and all that looking-up crap; people change stuff all the time, and don't change the codes. Take off the cover and look before you lay down your money and get it home and discover you just got sodomized.