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11" Drum Upgrade - Can You Do Just Front?

Discussion in 'Early CJ5 and CJ6 Tech' started by kenb, Nov 26, 2019.

  1. Nov 26, 2019
    kenb

    kenb Member

    Detroit
    Joined:
    Jan 22, 2019
    Messages:
    176
    Hello,
    I'm upgrading the brakes on my M38A1. It has the 4 cylinder engine, 5.38 axles, stock diameter tires. I'm getting an overdrive this winter.
    Is is possible to upgrade the front brakes to 11" drums and keep the rears at 9"? I remember from auto class that the front brakes do 80% of the work. I'm not sure if the expense of upgrading the rear brakes would have any real benefit.
    I have a functional transmission brake so I don't need a parking brake for the rear wheels.
    Thanks,
    Ken
     
  2. Nov 26, 2019
    Jw60

    Jw60 Recovering Jeepaholic

    Sedalia MO.
    Joined:
    Oct 5, 2018
    Messages:
    387
    Front 11s and rear 9 is better than all 9s.
    But you may consider front disk and put those 11s on the rear...
    (I hate eccentric 9s they never come out even)
     
    jeepstar likes this.
  3. Nov 26, 2019
    givemethewillys

    givemethewillys Sponsor

    New Kent, VA
    Joined:
    Jun 21, 2005
    Messages:
    894
    That's how mine is set up right now, made a huge difference
     
  4. Nov 26, 2019
    Howard Eisenhauer

    Howard Eisenhauer Super Moderator Staff Member

    Tantallon, Nova...
    Joined:
    Nov 22, 2003
    Messages:
    5,925
    Front 11's & rear 9's work very well- most of the braking force needs to be applied to the front anyhow & having 9" in the back literally guarantees the rears will never lock up ahead of the fronts causing a spin out.
     
    Last edited: Nov 26, 2019
    Rick Whitson likes this.
  5. Nov 26, 2019
    colojeepguy

    colojeepguy Colorado Springs 2019 Sponsor

    At the foot of...
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    Apr 4, 2010
    Messages:
    4,459
    That would be a good reason to upgrade the rear...self adjusting brakes. If you can find the 11" backing plates, the cost is not that much.
     
  6. Nov 26, 2019
    timgr

    timgr Jeepin' Nerd 2020 Sponsor 2019 Sponsor

    Medford Mass USA
    Joined:
    Aug 10, 2003
    Messages:
    20,352
    Hi Ken -

    In hard braking, the rears are mostly tasked with keeping the rear wheels from coming around and putting you into a spin. Most of the braking force is applied by the front wheels. When you have 11s front and rear, the cylinders of the fronts are larger by 50% so that front and rear tend to lock up at the same time. Jeep later (ca 1974?) added a proportioning valve for the rear wheels, which adds even more front axle bias in hard braking.

    One additional reason to go to the 11s in the rear is parts cost. The Bendix 11s were used on millions of vehicles, including the F100 Ford pickups. There's still a good market for these parts, and multiple brand-name suppliers. With the 9s, the market is limited to a few unmodified CJs still on the road, and you have few suppliers with little incentive to keep the price down and quality up (ie Omix).
     
    Last edited: Nov 26, 2019
    65CJ5 SRD likes this.
  7. Nov 26, 2019
    65CJ5 SRD

    65CJ5 SRD Member

    NM
    Joined:
    Aug 12, 2019
    Messages:
    101
    Parts availability on the 9's was a problem for me and one of the reasons I went with 11's all around.
     
  8. Nov 26, 2019
    Greevesman

    Greevesman Sponsor

    Napa, Ca
    Joined:
    Oct 12, 2014
    Messages:
    338
    I did 11" fronts. Big difference, easy job.
     
  9. Nov 26, 2019
    Jw60

    Jw60 Recovering Jeepaholic

    Sedalia MO.
    Joined:
    Oct 5, 2018
    Messages:
    387
    Parts availability and cost are why I went 4 wheel disk. caliper brackets are a lot cheaper and adjustment is pretty easy. It's a grind however getting the calipers to clear the knuckles. Now I need 3 point seat belts to keep myself from kissing the windshield.
     
  10. Nov 26, 2019
    mickeykelley

    mickeykelley Well-Known Member

    Republic of Texas
    Joined:
    Oct 10, 2015
    Messages:
    1,567
    The problem is not you kissing the windshield. It's the windshield kissing you back. Just saying.
     

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