Drum-drum 11" Poor Stopping

Discussion in 'Flat Fender Tech' started by vuldub, Aug 15, 2016.

  1. Aug 15, 2016
    vuldub

    vuldub New Member

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    I have a 1952 M38 with v6 231 with 31” tires. It was previously converted to 11” self adjusting drums, front and back with a single chamber master cylinder . When I got the jeep the brakes were scary – no stopping power so I overhauled them completely. New drums, new shoes, new wheel cylinders (1 1/8” bore in front and 15/16” bore in the back), new flex lines in the front, and a new single master cylinder 1 1/8” – brakes were still hard to stop. Swapped the 1 1/8” single master for the 1” single master and I had better stopping power, but the pedal is very hard and it’s difficult to lock up the wheels on gravel. Last winter I changed the 1” bore single master for a 1” bore dual master MC36239 (drum-drum dual – chambers are similar in size) for safety, but I had hoped the stopping might improve. It didn’t. Still have a very hard pedal. No room to install a booster. Thoughts?
     
  2. Aug 15, 2016
    Howard Eisenhauer

    Howard Eisenhauer Super Moderator Staff Member Sponsor

    Tantallon, Nova...
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    Welcome :)

    Still using the stock pedal & pushrod?

    The 1-1/8" MC is defiantly on the big side but 1" should be exactly right.

    Obviously, something isn't right. I have 11" drums, 1" & 15/16" front/rear & a 1" MC- they work just fine, I might even go to smaller wheel cylinders in the back.

    If you're used to power brakes then yes the pedal will feel hard anyhow but still you should be able to lock them up when you really want to.


    H.
     
  3. Aug 15, 2016
    vuldub

    vuldub New Member

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    No, it was converted to a hanging pedal and the MC is firewall mounted. I can stop and hold on a hill, but it's a very hard pedal - my wife doesn't like to drive it. I need to stand on it to lock the wheels. My buddy's CJ2a has a similar conversion, but he still has the frame mounted MC and his brakes are way better than mine.
     
  4. Aug 15, 2016
    Howard Eisenhauer

    Howard Eisenhauer Super Moderator Staff Member Sponsor

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    Do you know what the pedal ratio is for your setup, or what it came off of?

    H.
     
  5. Aug 15, 2016
    Alan28

    Alan28 Sponsor Sponsor

    Châtillon en...
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    I have a 'normal ' pedal and brakes, of course it is a little bit hard, but it works well. My son drives it too, and is not surprised by the brakes.
    It is not like his new car, of course, but the Jeep stops.
    Maybe your pedal systme is not well organised, maybe something else but I know the old brake system, it is my young years, and there is nothing mysterious in it. You should compare with an otyher similar Jeep to see where is the difference. And maybe the brake fluid but I don't see why.
     
  6. Aug 15, 2016
    Daryl

    Daryl Sponsor Sponsor

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    When you bleed the wheel cylinders do you get a forceful spray of fluid out of the bleeders?
     
  7. Aug 16, 2016
    vuldub

    vuldub New Member

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    Don't know what it is off. I measured it a while back and seem to remember 6:1 but I will remeasure tonight.
     
  8. Aug 16, 2016
    vuldub

    vuldub New Member

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    My buddy's CJ2a has a similar conversion, but he still has the frame mounted MC and his brakes are way better than mine.
     
  9. Aug 16, 2016
    vuldub

    vuldub New Member

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    I bled the cylinders into a sealed cup with a hose in and hose to the bottom of the cup (the one man method). If they weren't bled adequately they would have air in the line, which would produce a soft spongy pedal, not a hard pedal.

    When the wheels are off the ground, applying the brakes results in all four wheels not being rotatable. Also, there is no pulling to left or right when you stand on the brakes, they stop in a straight line.
     
  10. Aug 16, 2016
    jpflat2a

    jpflat2a what's that noise?

    Riverside CA
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    So how much freeplay do you have in the pedal before it becomes hard ?
     
  11. Aug 16, 2016
    tarry99

    tarry99 Member Sponsor

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    Pedal ratio is important 5-6:1 is in the ballpark..........1" master up front should be fine with a 15/16" wheel cylinders for 11" drums. If you think the brakes at both ends are properly bled and all else is fine.......then start looking at the non-obvious things like are the shoes correctly installed in each backing plate ..........some shoes can be reversed so that the leading edge is not correct..........Since these are new shoe's take a close look at the wear pattern on both the shoe and drum............sometimes the shoes will not be ground concentric in OD with the ID of the drum.............meaning your only getting partial contact with the friction surface............check it out.
     
    Last edited: Aug 16, 2016
  12. Aug 16, 2016
    Howard Eisenhauer

    Howard Eisenhauer Super Moderator Staff Member Sponsor

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    Depending on your setup it could take 800 to 1200 lbs of pressure at the wheel cylinders to lock things up.

    Let's say it's 1000 lbs, with a 1" MC thats ~ 785 pounds of pressure required to be applied to the MC, with a 6;1 ration thats 130 lbs of push from your leg to the pedal required.

    Stock CJ pedal ratios are around 6.5 to one-ish,

    Tarry made a good point about the shoes- if they're in backwards they don't work nearly as well.

    H.
     
  13. Aug 16, 2016
    nickmil

    nickmil Super Moderator Staff Member Sponsor

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    Also, with manual brakes you should be using organic friction material (shoes in this case). Any other type are too hard and will give poor braking just like you are experiencing.
     
  14. Aug 16, 2016
    Daryl

    Daryl Sponsor Sponsor

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    The reason I asked about pressure at the wheel cylinders was to see if you actually have hydraulic pressure. Nothing at all to do with whether they are bled or not. Hydraulic brakes need pressure in order to work. That will tell you whether you have a pump problem (MC or bad lines) or you have a brake pad material / glazed drum problem. Once you can find out what is actually happening the chances of solving your problem go up a little bit.
     
  15. Aug 16, 2016
    Alan28

    Alan28 Sponsor Sponsor

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    I hate to work on drum brakes because I remember my fingers crushed :(. I have a problem with mine and I gave the car to the pro-shop, he is more organized than me. One brake had a leak so it is repaired but the shoe is greased by the hydraulic liquid so I have to change it.
    I have a new shoe on the hand brake, all is perfect.
    The positioning of the shoes is to be checked carefully, tested by various means and the quality of the shoe must be adapted.
    All these parameters are interfering so I understand the problem, starting by the shoes which is easy to check. And modify.
     
  16. Aug 17, 2016
    vuldub

    vuldub New Member

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    Ah, I get your point now. Thanks. I do believe I have good hydraulic continuity to all wheel cylinders. Amount of pressure I cannot quantify. When it went to a dual master, I routed the rear and front separately so they no longer share a connection T, and nothing improved. That suggests it's not in the lines or inequality of pressure.
     
  17. Aug 17, 2016
    vuldub

    vuldub New Member

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    That was going to be my next action. Check out the wear pattern on the shoes. I will double check the shoes - primary (front facing) shoe should be smaller shoe. I can confirm there is no leakage on any shoes (that usually produces pulling as the non contaminated shoes grab preferentially). It might be awhile before I get into the brakes as I have another problem to deal with....
     
  18. Aug 17, 2016
    vuldub

    vuldub New Member

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    This is something I did not consider. I just bought the shoes that were listed. Will check out this.
     
  19. Aug 19, 2016
    fhoehle

    fhoehle Sponsor Sponsor

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    Just to add my two cents, I'd cut the drums and see if that helps. Boy, that glazing makes things quite a bit harder to woah. If you are right at 6:1 leverage, I wonder if possibly going to something with a 15/16 or a 7/8 bore would be excessive. I went manual brakes, and they are pretty light for manuals, with a 7:1 ratio. I do have a fair amount of pedal throw however. I'm going to do power brakes though.
     
  20. Aug 23, 2016
    jeeper50

    jeeper50 jeeps 'till I die

    Gawja
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    I found my flex lines collasped on my 2A recently while trying to bleed my new MC it had a very hard pedal, ordered both axle drop flex lines and wow what a difference on flow out to the wheel cylinders. brakes working normally now.
     

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