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12 bolt or 9 inch

Truth project
I love my Chevy Chevette!
Posts: 1
Joined: 06/15
Posted: 06/08/15 02:23 AM

I'm doing a Pro-Touring build on my 67.  500+hp LS with a 6sp manual trans.  I have a stock 12 bolt with drum brakes.  I know I need to ditch the drum brakes, but should I consider a 9 inch?  What are the pros and cons?  

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Just Try It1
My first time was in a Chevy
Posts: 165
Joined: 08/14
Posted: 06/08/15 07:58 AM

with a 9" rear end you get rid of the C clip axles.

you will be that much farther ahead..  you will also be able to use not just 31 spline axles you could order 35 spline axles.  so it will handle any abuse you might give it.

there are some serious axle housing designs... you are not stuck with a stock shape.

the 12 bolt has slightly less frictional losses but that only really counts for super speedway. and one of the manufacturers actually has a case that bolts into a 9" housing that uses 12 bolt gears..  so you can have the best of the 9" features and the reduced drag of the 12 bolt gear set.

type 9" into the search window above right.  see what pops up.

you did not mention if you are building a camaro. a chevelle. an impala. a pickup.

but housings that bolt in are available for almost any application..

the only good thing about drum brakes is the various wheel cylinder sizes available to fine tune the brake bias. this allows you to get it close before using the adjustable valve that can only reduce pressure to the rear wheels.  but who wants drum brakes on a pro touring car.. even if you can upgrade easily to 11" drum brakes .   on OEM 4 wheel disc brake cars..  that run all 4 tires the same size.. the front brake caliper pistons have very close to 66% to 33% for the rears..

if you are going to run bigger rubber on the back.. you will want to weigh the corners of the car.. measure the tire roll out.  the contact area of the tire contact surface and a dozen other calculations to dump that into a brake bias calculator to see if you can get calipers that will get you close..  

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