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Brake Front-REAR imballance

Discussion in 'Early CJ5 and CJ6 Tech' started by SRedinger, Mar 23, 2008.

  1. Mar 23, 2008
    SRedinger

    SRedinger Member

    Now Eugene, Oregon
    Joined:
    May 14, 2006
    Messages:
    96
    Description:

    My Jeep Brakes lock up the Back brake set when I stop hard-- Burn rubber.
    At the same time my fronts are not doing much wheels braking lightly-- but not locking the tires.

    All the system is bleed and I have lots of pedel.

    I Got 11" brakes on all fours.

    The Master Cylinder is on the firewall-- it is from a 1980ish Chevy 1/2 ton PU
    It is a dual master cylinder.

    There are two hydro fittings on the master cyl. One to the back brakes and One to the front brakes.

    The larger of the fittings goes to the back brake set. It is a 3/8 hydro fitting
    The fronts have 3/16 fitting

    Question--

    Is it reasonable to think that I should just trade fittings-- and thus the front brakes would brake harder-- while the backs brake lighter?

    Has any one else dealt with this situation?


    WILWOOD ADJUSTABLE BRAKE PROPORTIONING VALVE?

    Thanks-
     
    Last edited: Mar 23, 2008
  2. Mar 23, 2008
    w3srl

    w3srl All-around swell dude Staff Member

    Port Orange, FL
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    Nov 6, 2002
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    4,216
    Fist things first: The larger reservoir on the MC should be plumbed to the front brakes, this should be the one closest to the firewall. This reservoir is larger because the disc calipers use more fluid (bigger piston) than the drum rears.
    If you have these lines switched you will have exactly the symptoms you describe. ;)
     
  3. Mar 23, 2008
    bkd

    bkd Moderator Supreme Staff Member

    K-Town Tenn.
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    X2 I agree
    Jim S.
     
  4. Mar 23, 2008
    jpflat2a

    jpflat2a what's that noise?

    Riverside CA
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    Jul 30, 2003
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    8,409
    are you sure the front wheel cylinders are free, and not frozen up ?
    are you sure the brakes are adjusted properly, the shoes are contacting the drums before the pedal is applied ?

    if yes and yes, then carry on
     
  5. Mar 23, 2008
    SRedinger

    SRedinger Member

    Now Eugene, Oregon
    Joined:
    May 14, 2006
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    w3srl
    and
    bkd--

    Thanks and this is the case-- That is the fronts have the bigger reservoir . YOur feedback is appreciated. Driving an old Jeep is a real reality check for me after driving my supercharged Bonneville for years.

    I just ordered a Wilwood brake proportioning valve off of ebay for the Jeep-- seems like a solution---what do you think?

    Part of the Challenge with doing a frame-up rebuild it you put it all together-- then have a lot of bugs to get out of the whole vehicle-- expecially when you switched the engine, brakes steering-suspension and all of that plus more all in one big project. It is actually a real surprize that the Jeep works as welll as it does considering what a massive combo of untested parts it is built-up from and how CHEAP I did it.

    When I think about it ----the brakes are not really a perfect match for the MC. The MC was designed for a 1/2-3/4 Chevy truck that had discs in front and drums in back.

    I got 1967 front Bronco Brakes that are 11" on the back axle and 1974 Stock CJ 11" brakes on the front. The wheel cylinders on the back vs. the fronts may be as much as 1/4' dia different. The Bronco drums are somewhat different too-- they are very heavy and thick.
    This dawned on me after I just looked at the old parts I saved. I replaced the front brake cylinders with new aftermarket ones that I think are 1" dia (not sure) but I remember now that the Broncos were a little different size.

    Part of the problem may be that the brake shoes have not seated to the front drums yet. The Fronts have brand new drums and shoew the backs were arched-in and worn in . I got the bronco brakes from a neighbor who put a Dana 44 and disc brakes on his Bronco-- then the brakes sat for like eight years in my garage.

    Also I am running really small studded snow tires-- 215s these are only 27 -28 inches tall.

    I got a worn set of 31x10.5s I am going to mount in a couple of weeks. Then after the Jeep brakes and tracks good I will save $ for some better tires. I got 4-5 inches extra of wheel well clearance and could run really big tires-- even 37s. BUt that is too big.

    And part of my problem is that I was driving the Jeep in metro Denver, Colorado with BMWs,
    Hummers, Lexus, and sporty VWs flying all around like wild! Jack-Rabbit jump states and rapid panic stops are the way of driving in this place. 40-50 year old Jeeps and Trucks just cannot compete with agile commuters in this metro traffic. I drove a 40 mile circle to get the Jeep inspected and registared last week and it wore me out driving that old T-90 in big metro city traffic-- I was in a bumper to bumper for about 3 hours too. I live in an area right next to one of the wealthest urban areas in the Nation. Hummers and Escalades with 22" spinner chrome wheels--Brass chrome and coustom plates.

    But I am selling my metro Yuppy house and moving 1400 miles back to southern Oregon ASAP-- and I am going to become a Hippy again.

    Ever use a proportioning valve?
     
    Last edited: Mar 23, 2008
  6. Mar 23, 2008
    jpflat2a

    jpflat2a what's that noise?

    Riverside CA
    Joined:
    Jul 30, 2003
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    8,409
    the front wheel cylinders are typically much larger in diamter than the rears, say 1-1/8" vs 1" or even 3/4"
     
  7. Mar 23, 2008
    bkd

    bkd Moderator Supreme Staff Member

    K-Town Tenn.
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    Apr 29, 2007
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    3,292
    good points Jim...as I learned in my build all the components need to work, and work together......the joys of building from scratch is getting everything to work:D
    Jim S.
     
  8. Mar 23, 2008
    SRedinger

    SRedinger Member

    Now Eugene, Oregon
    Joined:
    May 14, 2006
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    96
    It could be that the rear brakes since adapted front Bronco brakes- thus the fronts from a heavier vehicle-- So after thinking about it the backs might naturally be giving slightly more braking than the factory 11" CJ brakes on the front.

    Part of my situation with such a customized vehicle made from so many different donor vehicles is brain storming possible bugs in the overall vehicle. So all of your feedback is very useful and appreciated.

    It is a real scarry thing to lock your screatching louding ripping rear tires-- and having your Jeep skid a long ways on its rears--- in heavy traffic toward possibly ramming some lawyers NEW 2008 LOW SLUNG CONVERTIBLE BMW who stopped on a dime in front of you. ( Though I must admit is it fun to see some fancy-dan lawyer who - (in his shiney sports boat--all groomed with slicked back hair, brute colone and 1000 dollar sun glasses) get the #$%&... scared out of him by an old red Jeep about to run him over. R) (as you see his eyes in his rear-view mirror-- watching at our quickly approaching bumper at his head level-- )--------( ASIDE FROM GETTING REALLY SCARED MYSELF)
    :oops:
     
  9. Mar 23, 2008
    bkd

    bkd Moderator Supreme Staff Member

    K-Town Tenn.
    Joined:
    Apr 29, 2007
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    I've got that unit on mine....you want the fronts to grab just before the rears...the P valve allows you to adjust the rears. I took mine to a gravel road and locked it up to see which wheels grabbed first, then adjusted the valve accordingly...takes some time but works great on my rig now.
    Good luck, Jim S.
     
  10. Mar 23, 2008
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor 2021 Sponsor 2020 Sponsor

    Medford Mass USA
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    Yep - the front brakes do most of the braking because of weight transfer, so they should have the larger cylinders. The master has to deliver the same pressure front and back, regardless of the volume of fluid delivered. A pressure imbalance would set off the warning light (if you had one). Force on the shoes gets larger the larger the cylinder is. A 1 1/8" cylinder makes 2.25x as much force as a 3/4" cylinder.

    I'm not sure that a disk/drum master cylinder is what you want. The disk brake wheel cylinder pistons are much larger than the drum brake WC pistons. I would use a drum-drum master if I had a choice. Since you have hanging pedals, I would use a drum-drum MC from maybe a '76 CJ.
     
  11. Mar 23, 2008
    SRedinger

    SRedinger Member

    Now Eugene, Oregon
    Joined:
    May 14, 2006
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    96

    Yes indeed.

    Testing your vehicle in a Metro area is really different from how I did it when I lived in a small rural town.

    Personally I do not like to drive a lifted narrow track Jeep on a Metro Freeway. And I avoid it.

    I did run the old CJ6 down Denver's Interstate 25 for about 5 miles at 60 mph-- and is was not a very safe feeling experience-- but it was OK-. FRONT END DID NOT SHIMMY even when hitting BUMPS!!!!


    BUt it is my belief that an old narrow track Jeep is a 45-50 mph designed vehicle.

    People drive their cars here like it was a raceway. Average speed 70-75- with a few always going like 80. If is often( in local news) that a very small agile car gets completely demolished by a heavy truck here in Denver. It is like an everyday thing on the evening news-- some little late model can pulls a quick lane change 'cut in front' with fast stop stunt in front of an 18 wheeler and is actually totally run over and completely transformed into shreaded sheet metal with chunks of wheel rubber, castings and human flesh. This happens when the lane the car changes into is suddenly slowed, just as the car switches into that lane-- yet the person still cuts infront of another vehicle. People who are in a hurry do not seem to realize that all other vehicles can NOT stop, accelerate or turn as quick and eazy as their little sporty cars.

    If this were to happen in front of an old Jeep on a metro freeway-- it would be a really bad day for Jeep, Driver and car in front and all directly involved.


    So with an old Jeep you want all your steering, suspension, and brakes to work as well as possible-- to avoid running into or having to to manuver beyond your vehicle's ability to stay upright. And you also want to avoid those kinds of traffic.

    But even 11" drums vastly our preform the old stock 9" stock brakes== and are pretty cheap and eazy to convert.

    And yea-- my front wheel cylinders are free and brand new and bleed. But thanks for asking/ mentioning.
     
    Last edited: Mar 23, 2008
  12. Mar 23, 2008
    SRedinger

    SRedinger Member

    Now Eugene, Oregon
    Joined:
    May 14, 2006
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    Yea--this could be a very good tip. I used a MC that I had quick had access to--
    It takes considerable pedel pressure to make the brakes work as it is now and very little foot pedal travel occurs.

    I wonder if other MCs have the same mount bolt pattern?


    IF not I could redrill-- or make an adapter.
     
  13. Mar 24, 2008
    AKCJ

    AKCJ Active Member

    Fairbanks, Alaska
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    Aug 12, 2003
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    1,033
    Why not just put on the adjustable proportioning valve?

    It's not very expensive or difficult.

    And it may keep your jeep out of the back of a BMW.

    I put mine under the dash so I can reach it from inside but it may be even easier to frame mount it. Once you get it adjusted you don't mess with it much.
     
  14. Mar 25, 2008
    jeeper50

    jeeper50 jeeps 'till I die

    Gawja
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