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My Theory Of Bore-dom - Brake Questions

Discussion in 'Flat Fender Tech' started by 46ODDFIRE, May 25, 2020.

  1. May 25, 2020
    46ODDFIRE

    46ODDFIRE Member

    Richmond, VA
    Joined:
    Aug 7, 2017
    Messages:
    125
    My latest archeological discovery and mystery continues all the usual themes:
    -- I broke something before the last repair (of something else) was even finished.
    -- I spent a ridiculous amount of time just getting one bolt or another loose (this time it was the the master brake cylinder fill plug).
    -- Almost no parts on my 1946 CJ2A are from a 1946 CJ2A.

    The quick review: My dad bought this CJ2A in 1969 and commenced to make and install lots of modifications. I now have the Jeep. Between my own mechanical mediocrity and the Jeep's Frankenstein's-monster modifications, I spend a lot of time just figuring out what the heck is going on. The Service Manual is of limited help, so I turn again to the EarlyCJ-5 brain trust.

    Getting to the point: I sprung a brake fluid leak in my rear passenger side wheel. When I got everything apart, there was crud caked on the cups and plungers. I was going back and forth among ordering a replacement cylinder (two, I guess), a cylinder repair kit (two, I guess), or holding off and trying to clean and reassemble everything (Cleaned up, the cups and plungers look great, and I have some reason believe the cylinders were serviced in the last five-to-10 years).

    REALLY getting to the point: While looking on the Kaiser-Willys site, I realized my cylinder bolts on differently than the stock cylinder. Then I realized that my Jeep does not have the 3/4-inch-bore stock rear wheel cylinders, or the 1-inch-bore cylinders from a truck or Jeepster. No, it has 1 1/8-inch-bore cylinders, apparently from the FRONT of a truck or Jeepster....?|

    Hmmmmm. Back in the day, I learned from my big brother that the Jeep was easy to put into a power slide when we rally raced along dirt roads. It was fun and easy to hang the rear end out, gas it and be off to the next turn. Not that that seemed surprising.... Flash forward to the last three years: When I've had to make a quick stop on pavement, one of the rear almost always locked up, made a big squeal and, more than once, scared the hell out of a pedestrian crossing the street.

    So: I'm thinking I have TOO MUCH braking power in the rear, relative to the front. Seems to me Dad may have done this for trails and rock crawling?

    Does anyone else think I should probably go down a size in the rear (assuming I'll also find 1 1/8-inch-bore cylinders on the front)?

    Also: What do folks use for the master cylinder filler plug? Is there a wrench with just the right offset (and maybe curve) to get a good purchase on that thing through the access hole? I ended up snaking a socket down between the engine and firewall, but that sucker was on tight, and it was difficult to get the socket on right.
     
  2. May 25, 2020
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

    Medford Mass USA
    Joined:
    Aug 10, 2003
    Messages:
    23,596
    The front cylinders are always larger than the rears. When you brake, weight transfers to the front wheels, and you need more force to lock the fronts than the rears. The rears need to be smaller so they don't lock up on hard braking and send you into a spin.

    Realize that the size of the cylinder is their AREA, so modestly smaller in diameter means a big reduction in area. I would copy the area ratio front-to-rear used from the factory in a '46 CJ-2A.
     
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  3. May 25, 2020
    46ODDFIRE

    46ODDFIRE Member

    Richmond, VA
    Joined:
    Aug 7, 2017
    Messages:
    125
    Thanks. That's my theory plan exactly. I don't know if my dad, or possibly my brother, did this for some reason, or what, and I suppose it doesn't matter.
    Also: Thanks to the moderator who changed my headline. My punniness left out the most-important word, "brakes."
     
    Focker likes this.
  4. May 25, 2020
    nickmil

    nickmil In mothballs.

    Happy Valley, OR
    Joined:
    Sep 23, 2002
    Messages:
    12,529
    To really be of help we need to know what diameter of brakes do you have. 9” that would be stock? 10” from a later Jeep? 11” from an even later Jeep? 1 1/8” front were common on 11” front drum brakes.
     
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  5. May 26, 2020
    jpflat2a

    jpflat2a what's that noise?

    Hermosa, SD
    Joined:
    Jul 30, 2003
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    8,513
    I suppose you need to tear into a front wheel cylinder and find out what diameter is up front.
    And, like Nick said, what diameter brakes do you have ?
    You can measure across the inside of the brake drum for the diameter.
     
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  6. May 26, 2020
    46ODDFIRE

    46ODDFIRE Member

    Richmond, VA
    Joined:
    Aug 7, 2017
    Messages:
    125
    Sorry, for everything I wrote, I left that out: 11-inch drums. I'll check everything out first, but it looks like I need to convert to 1-inch cylinders in the rear.

    Thanks, everyone!
     
  7. May 26, 2020
    Keys5a

    Keys5a Sponsor

    Florida Keys
    Joined:
    Jan 23, 2014
    Messages:
    4,170
    The brake wheel cylinder sizes also need to be matched to the correct master cylinder bore. Since your brakes have been "upgraded" to 11", I would be looking to duplicate the sizes used on factory 11" equipped Jeeps, maybe like found on a '72 model year.
    As far as your master cylinder, is it stock single-circuit on the frame rail? Yes, the original Wagner masters has a white-metal cap that tended to corrode with the iron casting, often crumbling apart when you try to remove it. Replacements used plastic caps that worked better.
    -Donny
     
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  8. May 26, 2020
    46ODDFIRE

    46ODDFIRE Member

    Richmond, VA
    Joined:
    Aug 7, 2017
    Messages:
    125
    Yes, the master cylinder is on the frame rail, and it appears to be stock. A plastic cap sounds like a good idea.
     
  9. May 26, 2020
    jeeper50

    jeeper50 jeeps 'till I die

    Spanish Fort. AL
    Joined:
    Dec 20, 2007
    Messages:
    844
    Mine has 7/8" on the rear, same as a 11" brake equipped 1975 CJ5 and I order all parts for that year model jeep.

    Also make a note to the inside cover of my jeep manual for future reference. This picture is the rear brake off that vintage jeep with emergency foot brake. It is also possible to have a front set of brakes (1/1/8 wheel cylinder) bolts up to the rear of your jeep. Does it have an emergency brake setup on the transfer case?
     

    Attached Files:

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  10. May 27, 2020
    46ODDFIRE

    46ODDFIRE Member

    Richmond, VA
    Joined:
    Aug 7, 2017
    Messages:
    125
    Yes, that's what I think I have: 1 1/8-inch-bore cylinders intended for the front but installed on the back. And yes, I have an emergency hand brake, though it has been disconnected and inoperable for years.
     
  11. May 27, 2020
    jpflat2a

    jpflat2a what's that noise?

    Hermosa, SD
    Joined:
    Jul 30, 2003
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    8,513
    75 CJ5 would have 15/16" diameter rear wheel cylinders.
    Nose picking....but that's what they were.
     
  12. May 27, 2020
    jeeper50

    jeeper50 jeeps 'till I die

    Spanish Fort. AL
    Joined:
    Dec 20, 2007
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    I was shooting from the hip with the 7/8 i recalled it was under 1"
     
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