GM 12 bolt rearend questions concerns

[BigChevyFTW]

i currently picked up a GM 12 bolt rearend for my chevelle

my concern is these articles that say they replaced the strait line rearend(12 bolt) for a 9 inch. can someone please tell me why they are saying this rearend isnt good for a corner carving GM A Body. thank you

[David Pozzi]

What articles???

[Rick D]

There are a lot of guys running 12 bolts on the auto-x and road. It's only 1/4 smaller then the 9 inch. You will be fine with the 12 bolt but as David said what articles?

[Amituk]

There is a good run down on 12s and 9s from jason at the GMR on my thread here

https://lateral-g.net/forums/show...t=37889&page=2

If you already have a 12bolt, I certainly wouldnt worry about it. Not a great deal in it really.

The only real advantage of the 9" that cant easily be replicated into a 12bolt is the easily interchangeable third member allowing easy track side ratio changes.

Amit

[SR71]

the 9" axles are retained by pressed on bearings instead of c-clips eliminating side to side axle play. thus the 9" doesn't suffer from pad knock back and has positive axle retention in the event of breakage.

if you are going to buy aftermarket axles, moser makes a kit that converts the 12 bolt over to 9" ford style axle retention.

[camcojb]

Originally Posted by SR71

the 9" axles are retained by pressed on bearings instead of c-clips eliminating side to side axle play. thus the 9" doesn't suffer from pad knock back and has positive axle retention in the event of breakage.

if you are going to buy aftermarket axles, moser makes a kit that converts the 12 bolt over to 9" ford style axle retention.

The 9" definitely has pad knock back issues, which is why Mark Stielow and companies like The GMR Co. spent so much time developing ways to eliminate it. Several of our members who track their cars have had issues.

http://thegmr.com/

[BigChevyFTW]

Thank all of you for your replies.

The article I read simply said " we ditched the 12 bolt strait line Drag Strip rearend for a Currie 9 inch.
that could have been a marketing ploy from the magazine.

The 12 bolt is like new with 3.73 gears i bought it from a guy who never installed it. only bad thing is the drum brakes so i will be replacing them soon and using the 12 bolt thanks fellas.

[David Pozzi]

On a 12 bolt with limited slip, a new unit will have no axle end play, a worn plate type will have some end play, re-shimming the clutch pack will reduce it. The Ford 9" has a better axle bearing but still has brake knock back problems. The cheapest solution is to use a floating caliper on the rear. If you want to use a fixed caliper, you need to install full floater axles.
David

[Vince@Meanstreets]

Originally Posted by BigChevyFTW

Thank all of you for your replies.

The article I read simply said " we ditched the 12 bolt strait line Drag Strip rearend for a Currie 9 inch.
that could have been a marketing ploy from the magazine.

The 12 bolt is like new with 3.73 gears i bought it from a guy who never installed it. only bad thing is the drum brakes so i will be replacing them soon and using the 12 bolt thanks fellas.

Might have already been set up for drag racing ie: spool, numerically high ratio so it was problably a bit cheaper to go with the 9.

[Flash68]

Originally Posted by David Pozzi

On a 12 bolt with limited slip, a new unit will have no axle end play, a worn plate type will have some end play, re-shimming the clutch pack will reduce it. The Ford 9" has a better axle bearing but still has brake knock back problems. The cheapest solution is to use a floating caliper on the rear. If you want to use a fixed caliper, you need to install full floater axles.
David

This guy knows what he's talking about.