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MC questions

Discussion in 'Early CJ5 and CJ6 Tech' started by Project71-5, May 30, 2005.

  1. May 30, 2005
    Project71-5

    Project71-5 BACON

    Gypsum, CO
    Joined:
    Sep 24, 2002
    Messages:
    897
    Does anyone know what size bore a stock dual chamber MC is?

    And I know this next one is pretty specific but how about the distance between the mounting holes on the dual chamber MC?

    I'm trying to figure out what other MC will bolt in with little or no modifications. Thanks fellas!
     
    Project71-5, May 30, 2005
    #1
  2. May 31, 2005
    jeepdaddy2000

    jeepdaddy2000 Active Member

    Eagle Point oregon
    Joined:
    Jun 24, 2004
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    1,187
    I replaced my OEM dual MC on my 71 with a 72-75 drum unit. Switched out the rod and boot. Direct swap. Rebuilt MC cost me 18$.
     
    jeepdaddy2000, May 31, 2005
    #2
  3. May 31, 2005
    Mcruff

    Mcruff Earlycj5 Machinist

    Albertville, AL
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    Sep 22, 2002
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    5,349
    I think Joe's point was for the disk brakes up front, he just forgot to mention it.;)
     
    Mcruff, May 31, 2005
    #3
  4. May 31, 2005
    jeepdaddy2000

    jeepdaddy2000 Active Member

    Eagle Point oregon
    Joined:
    Jun 24, 2004
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    I would imagine that a disk brake version of the above mentioned MC would work as well.
     
    jeepdaddy2000, May 31, 2005
    #4
  5. May 31, 2005
    w3srl

    w3srl All-around swell dude Staff Member

    Port Orange, FL
    Joined:
    Nov 6, 2002
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    4,275
    Just remember that if you use a MC from a Jeep that is later than a '71, be sure that the unit you pick has the brake line outputs on the correct side of the MC. Every MC I saw that was later than '71 had the lines coming out of the inboard side of the MC (passenger side) while the disc brake units had them on the outboard (driver's side). This is no big deal if you are running a hanging pedal setup, but if you still have through-the-floor pedals you *REALLY* want the lines coming out on the passenger side. This means using a drum-brake MC and changing out the RPV on the rearmost port to use with the front discs.

    Trust me fellas, BTDT. Got a DRAWER full of the t-shirts! :D
     
    w3srl, May 31, 2005
    #5
  6. May 31, 2005
    Project71-5

    Project71-5 BACON

    Gypsum, CO
    Joined:
    Sep 24, 2002
    Messages:
    897
    Yeah I have disks up front and 11" drums in the rear. The stock MC stops them but it is really mushy mainly because it doesn't flow enough volumn.

    I really would like to try a CJ disk/drum unit but the lines are the main thing because I still have the underfloor unit. I'm sure a 72-75 unit would work if I removed the RPV.

    I even thought about looking for a Wilwood unit which is why I asked about the mounting hole centers. Thanks guys!
     
    Project71-5, May 31, 2005
    #6
  7. May 31, 2005
    Mcruff

    Mcruff Earlycj5 Machinist

    Albertville, AL
    Joined:
    Sep 22, 2002
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    5,349
    Joe be sure to keep the part number if you find one that works, cause I have the same problem.
     
    Mcruff, May 31, 2005
    #7
  8. Jun 3, 2005
    Mcruff

    Mcruff Earlycj5 Machinist

    Albertville, AL
    Joined:
    Sep 22, 2002
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    5,349
    Joe I measured the distance between the mounting bolts on my drawing for the brake bracket, the bolts on the flange are spaced 3.375" apart.
    Found this link, it might help, they have quite afew MC with the brake line holes on both sides.
    http://www.hotrodsusa.com/store/mastercylinders.html
     
    Mcruff, Jun 3, 2005
    #8
  9. Jun 3, 2005
    w3srl

    w3srl All-around swell dude Staff Member

    Port Orange, FL
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    Ya know, I've been wonderin' about this. The '77-up drum MC fits like a champ and does work, but I've never really go tthe pedal I was happy with. Mind you, It's rock-solid, but like Joe said, the volume just doesn't seem to be there. There's gotta be another MC out there that is dual-chamber, has the ports on the passenger side, and has a big enough bore to drive discs well......

    The wheels be a turnin' now! :shock:
     
    w3srl, Jun 3, 2005
    #9
  10. Jun 3, 2005
    Mcruff

    Mcruff Earlycj5 Machinist

    Albertville, AL
    Joined:
    Sep 22, 2002
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    5,349
    Well I talked to the friend of mine that I got my dana 30 with the disk from today, he said that with that stock setup before I got it, he always had a soft pedal and it never felt good and firm to him and his setup was completely original when he bought the jeep, so maybe they were borderline from the factory.
     
    Mcruff, Jun 3, 2005
    #10
  11. Jun 3, 2005
    w3srl

    w3srl All-around swell dude Staff Member

    Port Orange, FL
    Joined:
    Nov 6, 2002
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    Ok, I'm on a mission now. :rofl:

    So what is the original bore size, anyone know?

    And am I correct in thinking that a smaller bore is going to give more pressure, but less volume?

    If that is the case, and given that the 1/2-ton GM discs border on overkill for a 2800-pound Jeep, then I think I'd be tempted to go with the largest bore I can get.

    Idears?
     
    w3srl, Jun 3, 2005
    #11
  12. Jun 3, 2005
    william_cj3b

    william_cj3b 3BOB driver

    Milton, FL
    Joined:
    Nov 17, 2003
    Messages:
    421
    OK - this is something I've been doing my homework on for a few weeks now. And yes, homework can be fun if it requires multiple field trips to all your favorite salvage yards ;) Some of my info may be incorrect or incomplete, so chime in freely to correct.

    Original (77-78, maybe later) Jeep master cylinder w/ front disc had a 1 1/16" bore. All drum brake CJ's (68?-78?) had a 1" bore. GM trucks w/ manual disc brakes also used a 1" master cylinder.

    Yes. The brake hydraulic system is essentially a glorified lever. The higher the ratio of piston area (caliper/wheel cyl. over master cyl.) the longer the lever. ??? clear as mud????

    With oversized tires I would have to say that they're anything BUT overkill. The GM disc brakes are not any bigger than the CJ disk brakes (except maybe for pad area, I haven't compared this yet) The GM calipers also have a smaller bore than the CJ ones (GM - 2 15/16", CJ - 3 1/8") which means higher fluid pressure is needed.

    The K10 trucks used a master cylinder with a 1" bore for manual brakes and 1 1/8" bore w/ power brakes. Wagoneers used the same 1 1/8" master cylinder (same PN) and had nearly identical calipers (same bore, same pads and mounting bracket - I think the only difference is the brake line fitting)

    I plan, in the very near future, to put discs on the Jeepster and install a Wagoneer booster and master. Along with 11" rear drums (which use a wheel cylinder of the same size as rear Wagoneer brakes) I should be able to assemble a "factory matched" Wagoneer brake system with a 5 lug pattern on a Jeepster. I am still considering a smaller wheel cylinder on the rear to reduce lockup, but will probably wait and see what the initial result is. There are SEVERAL different size wheel cylinders that will fit 11" backing plates.

    Confused......???? I know I am :oops:
     
    william_cj3b, Jun 3, 2005
    #12
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