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Help confirm my thoughts here..

Discussion in 'Early CJ5 and CJ6 Tech' started by cj566, Jan 6, 2009.

  1. cj566

    cj566 New Member

    I have researched this topic a lot the last couple of weeks. I upgraded my brakes to 11" drum brakes all around on my 66cj. I got a good deal on a pedal assembly from an 89 wrangler. It has the clutch master and booster as well. It's a nice setup.Will require some pedal mods but nothing major. Anyway I planned on using a master cylinder from a drum/drum application on the booster. After a long search by my friends at my local NAPA store, all of the drum/drum master cylinders they had (which is a lot) will not mount to my booster. The center to center on the mounting holes is different on all they had. My thinking is i can just use the disk/drum master cylinder from the 89 wrangler and plumb a 10" rpv to the front brakes. Is my thinking correct???????

    I just wanted to extend my thanks to all you ECJ members who have provided so much info to me during the rebuild of my CJ. I don't ask many questions on the forum but the search function provides so much info I don't need to.

    Thanks again,Steve
     
    cj566, Jan 6, 2009
    #1
  2. floor ya

    floor ya NOT. a junior anything

    some one correct me if i'm wrong. but you should be able to use a adjustable proportioning valve and fine tune to your drum/drum.
     
    floor ya, Jan 6, 2009
    #2
  3. w3srl

    w3srl All-around swell dude Staff Member

    That's not entirely correct. An adjustable proportioning valve will alter the front/rear bias but do nothing in terms of maintaining pressure in the lines once the pedal is released.

    The correct way to do this would be to remove the 2# RPV in the MC port that feeds the front brakes (rearmost port on the MC) and then plumb a Wilwood 10# RPV into the line feeding the front brakes. The rears should be fine.
     
    w3srl, Jan 6, 2009
    #3
  4. cj566

    cj566 New Member

    Thanks for the reply's Steve and Floor ya.

    Steve I was under the impression that there was not an 2# RPV in this MC because it is firewall mounted and would therefore not require one...as the MC would have been above the calipers...

    And is an adjustable proportioning really necessary for a drum/drum setup????? Would the use of the disk/drum MC on the drum/drum setup require an adjustable proportioning valve for some reason ??????

    Steve
     
    cj566, Jan 6, 2009
    #4
  5. w3srl

    w3srl All-around swell dude Staff Member

    You may be right about the RPV, personally I wold plumb it all up and give it a try without the RPV. If there is a need to have a 10# RPV in the front brake line, you will have a poor pedal and have to double-pump the brakes to get a good feel/stop out of it. You do want to be careful about having two RPVs of different values in the sam eline, that can really mess things up performance-wise, since the two valves would be inline with each other.

    And no, I don't think you will need an adjustable proportioning valve either, but I would be cautious about hard stops until you see how it all behaves. If it locks up the rears before the fronts then you will need some restriction in the rear line to even it out.
     
    w3srl, Jan 6, 2009
    #5
  6. Boyink

    Boyink Super Moderator Staff Member

    Just FWIW - I used the drum/disc power setup (including the proportioning valve) out of a late CJ7 on my drum/drum CJ5 without any mods to the master cylinder and it always worked fine.
     
    Boyink, Jan 6, 2009
    #6
  7. Warloch

    Warloch Did you say Flattie??? Staff Member

    You are correct there - I have done a couple in the last few years (convert floor pedals to the firewall) and have not had to use RPVs on any of them. I even have a proportioning valve (willwood) that I thougth I would need with my single feed setup, the different size pistons on the drums and the disc - drum combo have taken care of it.

    As said - test carefully - then decide if you need them.
     
    Warloch, Jan 6, 2009
    #7
  8. cj566

    cj566 New Member

    Thanks for all the info everyone. It will be trial and error. I'll make it happen. And I'll be careful.

    Steve
     
    cj566, Jan 7, 2009
    #8