I just wanted to know I read elsewhere that a 91 with gu2 rear had 2.73s and I read some where else that they came with 3.45s with POSI just want wanted know if the gearing is orginal or if its been changed to a 3.42 rear because I did count driveshaft rotation and it came out to around 3.42s thanks

 

If that's yours in the pic, Count the teeth on the ring and pinion then do the math. Or tooth count should be on the ring gear.


Factory would have been 2.73 but if you don't know the cars history then yes, they could have been changed.

 

That's a posi FWIW; the POS stock Auburn one, that most likely is toast like all the rest. Judging by how much of the driver's side axle is exposed I'd say it probably is.

The carrier looks 2 series to me.

Look around the edge of the ring gear for numbers something like 15:41. That'll tell you the gear ratio that you have. If I saw them in your pic I could tell you your ratio but your carrier is turned to where they're hidden. Post em when you find em.

 

then the rear has been changed out to 3.42s I don't know where they came up with the 3.45s at unless thats some kind of berlinetta rear

 

ive never had any problems out of this rear end really it still lights both tires up and its not making any noise ive put 6000 on it since beating the ever living **** out of it maybe I just got lucky but if it is really junk I'll just go straight to 4.88s I don't plan on any long drives any way

 

If that's 3.42s then you already have about the best gear for the low-revving TPI setup already. 4.88s would be overkill its not like you are pulling 7000rpms.

 

What are the numbers on the gears? Or, what are the tooth counts? (same thing) Effff "drive shaft rotations", there's too many ways to screw that up. You can get lucky and get it right, but then again, maybe not.

No point in guessing about what gears you have. You either KNOW or you don't. Look at the {ARTS. Nothing else matters.

3.45 is a 9-bolt ratio. Not available in the 10-bolt (which is what you have).

To my knowledge none of the 91s came with 3.42 but I could be wrong. And of course, people can always swap them, so no matter what "codes" you have, there's no guarantee that they still apply to your PARTS.

Availability of posi was completely separate from gear ratio in these cars. Some cars, being more "performance" oriented than others, were of course more likely to get it; but it was common in 305 auto cars with TPI and 2.73 gears, the lowest of the low among TPI setups.

4.88 gears with TPI will produce a setup that will launch from 0 - 30 in about a tenth of a second if you have traction, but won't be able to go faster than about 60 mph, with your foot on the floor and a 5 mile stretch of road. As said, 3.42 is about the best for the TPI motors with the better cam, and 3.23 for the others. I know the 305 5-spd cars with G92 got that cam, in some years; not sure which of the others or what years.

You can "test" your posi by putting the axle tubes on jack stands, putting the transmission in park, and trying to rotate one wheel with a lug wrench. Brand-new, that Auburn POS took around 65 - 70 to turn, once it was started turning (not "breakaway" or "clicker" torque, but SUSTAINED while moving). Below about 50 or so indicates that the clutches are worn enough that the springs no longer have tension. As the clutches wear, the side gears sink deeper and deeper into the carrier, exposing more and more of the end of the axle. Judging by the amount of the end of the axle exposed in yours, looks to me like there isn't much clutch left.

Look at the parts, and measure the torque. Nothing else matters.

 

You're right about one thing; you definitely won't be going on any 'long' drives with that gear ratio. It's your car, but with a TPI engine---and the relatively short tires on a 3rd gen---the car will become basically undriveable.

 

oh sorry I forgot to mention this is just strictly a drag and oval racer now and the tpi is gone .I did manage to get a vortec block and cam to work on it and a tbi motor to work with the tpi it has a carb crane 274h06 cam dual plane dart 2 intake and world heads and open headers the 350 motor came out of a 93 roadmaster with 10900 miles