I'm new to rear ends. I'm wondering if I need a 2 or 3 series carrier? I have 91 camaro rs with the stock 3.08 gears .

 

Series 2 for stock gears 2.73-3.08.
Series 3 for stock gears 3.23-3.42.

Series 3 can fit a series 2 with a spacer. IIRC 1/4".

 

Will a 4th gen carrier fit in a 3rd gen? They're both 7 5/8..

 

Yes, it will fit. The '91 also has 28 spline axles. This is where you have to be careful. The '89 and earlier 7 5/8 and 7 1/2 inch rear ends had 26 spline axles and the '90 and later had 28 spline axles.

The 2 series is for 2.14 to 3.08 gears and the 3 series is for 3.23 to 4.56 gears. There are special thick 3.23 to 4.10 after market gears that are made to fit the 2 series differental, but this does not apply to GM gears.

 

So if your going from 2.73 to 3.73, you need a spacer? can that spacer also be purchased on summit?

 

DO NOT use a spacer. They are nothing but trouble, especially in the 7.5 rear end. There are special gears for the 7.5 that are made thicker for use on the 2 series differential.

 

thanks big gear head. that idea is out now. dont need ANY trouble back there. summit gave me the option to choose 3.73 for a series 2 carrier so that should take care of everything. here's the link in case others in my shoes need it:
http://www.summitracing.com/parts/sum-741012

 

Do they make a 3.42 ring and pinion for a series 2 carrier?

 

Yes.

 

I have 9 bolt with 2:77s You said summit had 3series for 2series

 

Not for the 9 bolt. The thick gears are only for the 7.5 10 bolt. You will need a 3 series differential for the 9 bolt.