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Dual chamber MC question

Discussion in 'Flat Fender Tech' started by garage gnome, Mar 8, 2011.

  1. Mar 8, 2011
    garage gnome

    garage gnome Rust polisher

    Western MA
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    I've been thinking about upgrading the stock single chamber MC on my 3A to a dual one using Herm's kit. But I've been wondering, is a proportioning valve necessary (or a good idea)? :? I've searched the threads, and none of them mention using one. I would think that the rears would lock right up when the brakes are applied since there is barely any weight back there.
     
  2. Mar 8, 2011
    w3srl

    w3srl Semi-homeless in Florida Staff Member

    Port Orange, FL
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    Nope, been running without one for 6+ years.
     
  3. Mar 8, 2011
    mdmeltdown

    mdmeltdown Member

    Bossier City,...
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    Mine don't lock up, but if you really hammer down on the pedal they do, but then so do the front from what can tell
     
  4. Mar 8, 2011
    Howard Eisenhauer

    Howard Eisenhauer Super Moderator Staff Member

    Tantallon, Nova...
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    Not required as your (assuming stock 9" brakes) wheel cylinders are different sizes front to back, 1" vs. 7/8" IIRC. This means that for the same pressure applied to each end the rears generate less pressure to prevent rear lockup.

    FYI at least some later jeeps with 11" brakes used the same system postal jeeps for example. Others used the same wheel cylinders on both ends with a proportioning valve. The tricky part is some that came with the different sized cylinders also have a doohickey plumbed into the lines to trigger the dash light if one side develops a leak, people see these thing & assume they're a proportioning valve, this can lead to all sorts of fun when performing a transplant :)

    H.
     
  5. Mar 8, 2011
    garage gnome

    garage gnome Rust polisher

    Western MA
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    I'm using 10"ers out of a '66 CJ5.


    While doing some more searching about installing Herms kit, I found this on the 3B page:

    But like w3srl said, he's been fine for 6 years.
     
    Last edited: Mar 8, 2011
  6. Mar 9, 2011
    w3srl

    w3srl Semi-homeless in Florida Staff Member

    Port Orange, FL
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    Actually, I have a proportioning valve in the rear line but it's cranked wide open. Stock 9" rear drums and GM discs up front.
     
  7. Mar 9, 2011
    nickmil

    nickmil In mothballs.

    Happy Valley, OR
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    There's a lot of variability whether you need a proportioning valve or not. I suspect Steve's is cranked wide open because of the small rear brakes. Less likely to lock up. When I had discs on the front and 11" drums on the rear I didn't have one, still don't with disc/disc but probably should have one as the rear locks up just slightly before the front. I have run into some conversions I've done that did need one on the rear though or they would lock up. I'd try it without first. You can always add it if needed.
     
  8. Mar 9, 2011
    duffer

    duffer Rodent Power 2019 Sponsor

    Bozeman, MT
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    I'm running disc/disc on the 3B and installed a Wilwood unit below the dash. It did make a difference and I suppose you could even change the bias based on loading, but something I have never found necessay. To me, it's not worth having to rebleed the brakes a second time if you put it together without it and then find you probably need it. Not a big expense.
     
  9. Mar 9, 2011
    Hawkes

    Hawkes Member

    Nova scotia
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    Piratejack.net sells adjustable proportioning valves on ebay, they go for cheaper than their website. Mine should be here any day, and with shipping to Canada it was still cheaper than their list price. They can be hard to contact by phone but an ebay purchase is easy.

    I have rear drums and front rotors, and it's 50/50 which ones lock up first. Since I drive on ice and mud I want the fronts to always lock up first.

    edit: I just went to power brakes from manual, with the manual brakes they never really locked up, so it may not be an issue anyway.
     
    Last edited: Mar 9, 2011
  10. Mar 9, 2011
    garage gnome

    garage gnome Rust polisher

    Western MA
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    Alright, thanks Gents for the input. I think I'm going to put the dual chamber MC in without it and see. I want to be able to push the brakes when towing my trailer and know I'll be safer when I stop... Hopefully. :)
     
  11. Apr 16, 2011
    garage gnome

    garage gnome Rust polisher

    Western MA
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    I finished putting the dual MC in today, but I have another question. How far should my pedal move? It stops at about 1" before the floor board and is solid. There is no air in the system and the brakes are all properly adjusted. With the old single one, the pedal moved about 1" before it got solid.
     
    Last edited: Apr 16, 2011
  12. Apr 16, 2011
    windyhill

    windyhill Sponsor

    PA
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    Did you bench bleed your master cyl. before you installed it?
     
  13. Apr 17, 2011
    garage gnome

    garage gnome Rust polisher

    Western MA
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    Yep. The pedal doesn't feel spongy at all.
     
  14. Apr 17, 2011
    garage gnome

    garage gnome Rust polisher

    Western MA
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    While I was eating breakfast, I came up with an idea. I took the return spring off to see if there was any free play with the push rod. Yep, there was about 1". Solved that and now it is much much better.
     
  15. Apr 17, 2011
    windyhill

    windyhill Sponsor

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    Smart little wipper snapper an't you!:) Nice Job.
     
  16. Apr 22, 2011
    57cj5

    57cj5 Member

    North Carolina
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    Just curious on a couple of things. I also have his dual res. MC and discs up front with the 11 inch drum rears.
    1) did you have to shorten the rod from the brake pedal to the MC? My first one was cut and welded together to make it shorter. I felt this mod a little unsafe. I then tracked down some used rods (both ends) and cut one down the threaded one to the right size and threaded it all the way to the eyelet. Now it fits without any welding and is just as strong. I got that idea from someone else who did it this way.

    2) I have semimetallic pads up front but will be switching to organic. I read and was told that organic pads are for manual brakes whereas all others are for boosted brakes. They say with organics you can stop much better.

    3) I run a proportioning valve in my set up. Seems to be working great for me.

    Paul
     

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