Hey guys i just have a couple of questions, about a rear I just bought off of ebay. It is a posi rear from an 87 trans am with 3.73's. I have right now in my car a 3.08 rear non posi. so i guess my question is how much of a difference should i expect and how bad am I going to kill my gas mileage now with the 3.73's. I have a t-5 transmission by the way. Thanks for any input.

 

what mpg were you getting before?

 

I was getting about 17-18 mpg with the 3.08's

 

It won't be too bad on the gas mileage if you can keep your foot out of it. You might have a hard time since it will accelerate better and you cna roast the tires easier (not that it's hard anyways).

 

blue

I went from 2.73's to 3.73's and it made a huge difference in acceleration

 

you'll like the 3.73s.

87 T/As didn't come with 3.73s stock, I don't believe.

 

First thing you should do before you put it in your car is take off the cover and inspect everything and change the fluid. While you're doing that, make a point of looking for the numbers stamped on the edge of the ring gear, or count the teeth.

I'd almost be willing to bet that it doesn't have 3.73s, unless they've been changed. I don't believe any of those cars came with a ratio above 3.42, and those are pretty hard to find, would probably actually have been a 3.45 9-bolt (305 TPI 5-speed only).

Better count the teeth before you pay the bill.

 

Thank you guys for all of your help. I am going to go july 6th to pick up the rear. They are not the stock gears in the rear, the seller had 3.73's put in. Thanks again for all of your help.

*edit* thanks mdformula

 

you better hurry up ur 23 days late j/k

good luck with the new rear.