So..I have a 9 3/8 12 bolt rear..options?

Discussion in 'Got gears?' started by lwalling, May 14, 2019.

  1. lwalling

    lwalling Member

    Hi All,

    Doing a big car project(71 electra), have an awesome 455 already installed and going 4l80e shortly.

    Knowing what I know about the 9 3/8 rear end I have a few options. Am I right? Can you help direct me in the right directions?

    1) Find a 71-72 Riviera GS posi rear with 3.42 gears. Any line on one if I'm right?

    2) Fab a 9 inch Ford or 12inch Chevy rear to fit. I'd like to keep my stock bolt pattern wheels, but also fit some small discs. Any vendors that are a good fit for something like this for a big car?

    3) Hopefully more ideas!

    Thanks in advance.

    70 GS Stage 1
    71 Electra
  2. Smartin

    Smartin Staff Member

    Find a 71+ big Buick with a factory 350. It has an 8.5” rear and is a direct bolt in. Gears are available for that.
  3. lwalling

    lwalling Member

    Any reservations with a 8.5 knowing the power plant is making 500+ hp?
  4. cjeboyle

    cjeboyle Gold Level Contributor

    Ther are lots of people on here running a lot more power than that with 8.5’s. I would think you would want to get new gears and an Eaton or similar posi to put in the 8.5 housing. Maybe Monzaz will chime in. He is one of the rear end specialists on this site and is where I purchased mine.
  5. BrianTrick

    BrianTrick Brian Trick

    The 8.5” 10-bolt is one of the best rears ever made. They can take plenty of abuse,and there are plenty of aftermarket parts available.
  6. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    I have an 8.5 10 bolt in my car. It has an Eaton 30 spline Posi Carrier and Moser 30 spline axles.
  7. monzaz

    monzaz Jim

    I have a few 10 bolt 8.5 rears for FULL size car on the shelf.
    All depends on what you expect.
    If your talking tack time and a 12 sec or faster BIG CAR 4000+ weight slicks higher stall you had better spend so money on a good rear.

    But if your talking street mostly and some fun runs on the weekend during the year the 8.5 will do the job.
    on the street we really do not worry much as the torque never really hooks, you can have 1000 hp and will never grab the ground so it does not matter.

  8. lwalling

    lwalling Member

    Thanks all. Found a 3.42 9 3/8 posi here on the forum. Pretty excited about it. The car isn't a drag car, but it's making good power and it will be driven plenty. Have a ton of parts coming together now. The motor is already in and runs great, mostly all TA Parts (Stage 1 heads, roller drivetrain, modest cam, etc) and a 6L80E being built to put behind it. This should be a really fun trip car when done!
  9. monzaz

    monzaz Jim

    That is impressive find. :) Make sure you get a good set-up as finding more of those gears are getting rare to find.
    MAKE sure you get them right on so they last.
  10. Smartin

    Smartin Staff Member

    Hopefully the rear came from a 71+
  11. lwalling

    lwalling Member

    Yep, it's the old listing from 2016 by @EEE - was still available.
  12. Smartin

    Smartin Staff Member

    Perfect! Kimson is a great board member.
    72GSX4ME likes this.

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