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Hot Rods Fixed Brakes... reason they didn't work

Discussion in 'The Hokey Ass Message Board' started by wallster, Aug 16, 2019.

  1. wallster
    Joined: Aug 3, 2012
    Posts: 56

    wallster
    Member
    from Buffalo NY

    I've owned this '32 Ford for a couple of years and I've posted all the brake issues I've had with it since the day I bought it. First and foremost the front disc brakes would eventually lock up and I'd have to open a caliper bleeder to relieve the pressure, then I was good for a little while. The car never did stop that great but worked well enough to drive. I replaced calipers, front hoses, the line flares were poorly done so I replaced all the brake lines and changed residual valves. I even added a proportioning valve for the rear drum brakes but still it didn't brake worth a shit. Upon digging into the problem I found that the power booster rod was advanced well into the MC giving it a preload which was the reason for the brakes building pressure and locking up the brakes. Two days ago I was thinking that I needed to look elsewhere so I unbolted the master cylinder and set it on wood blocks so I could see the power booster rod. When I depressed the brake pedal the booster rod protruded barely 3/8". The problem was all in the pedal because it would bottom out on the bottom of the car (when idle) and when pushed all the way in it wouldn't throw the rod far enough into the MC. I pulled the pedal assembly off and cut it so that it had approx three inches sticking out from under the firewall. I drilled two 1/4" holes in it 1" apart. Then I cut the curved end of the pedal at the base to open up the upright angle and then "massaged" the curve that enter the firewall. I added about three inches of steel to the pedal end. I welded the shit out of the pedal once I had my clearances and cleaned everything up. Sandblasted it and painted it. Once dry, I bolted the two together with (2) 1/4"-20 SS nuts and bolts and now the rod extend almost 1". So the original builder didn't have his ratio correct and didn't bother fixing it but rather preloaded the booster rod so the brakes would stop the car. Thanks for everyone's advice and if you're in the same boat with your brakes check out how far the brake stroke is because you might have a similar situation. I feel stupid that I didn't check it first but it just didn't dawn on me that someone could have gotten this so wrong when putting the car together. (See pics, the before photo was taken when the builder was finishing the car)
     

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    s55mercury66, pitman, jazz1 and 4 others like this.
  2. Thanks for the update and the details on what it took to make things work as they should. For as many cars here that get new brake systems swapped onto them, and the number of people that end up with brake issues, it's good to see somebody take the time to diagnose the problem all the way back to the brake pedal. ;)

    It seems that too often the owner just wants to throw money at the problem and when he doesn't find the root cause and fix it properly, he just learns to live with it. :oops:

    You have to know how this stuff is supposed to work before you can figure out why it doesn't. :rolleyes:

     
    osage orange and wallster like this.
  3. Ebbsspeed
    Joined: Nov 11, 2005
    Posts: 6,250

    Ebbsspeed
    ALLIANCE MEMBER

    Glad you got it figured out. One thing i would be concerned with are the two 1/4 inch bolts 1" apart holding the pedal arm together near the pivot point. I think I'd be inclined to use larger diameter bolts.
     
  4. Weld it, , the shear strength of 2 1/4-20's ain't enuf.
     
    King ford and Black_Sheep like this.

  5. wallster
    Joined: Aug 3, 2012
    Posts: 56

    wallster
    Member
    from Buffalo NY

    IMG_9430.jpg
    I replaced them with 3/8” SS bolts... good call, thanks!
     
    Last edited: Aug 19, 2019
    Boneyard51 likes this.
  6. wallster
    Joined: Aug 3, 2012
    Posts: 56

    wallster
    Member
    from Buffalo NY

    The problem with welding them is even with taking the steering column out there's not enough clearance to get that assembly in there in one piece.
     
    Frankie47 likes this.
  7. X-cpe
    Joined: Mar 9, 2018
    Posts: 1,958

    X-cpe

    One cardinal rule when designing/building brake systems is that the MC piston should bottom out before the pedal hits the floor.
     
  8. bschwoeble
    Joined: Oct 20, 2008
    Posts: 1,015

    bschwoeble
    Member

    My buddy and I work on all varieties of "special interest " cars. The biggest complaint owners have, after buying a car, are the brakes. Many, many people think they know what there doing, when engineering the brake system. I'm not saying we haven't made mistakes, but we have learned to take nothing for granted. Especially when using off shore parts, which is mostly unavoidable. If you believe what you read, the rod out of the brake booster should be .0010 to .0015 thousands free play to the master cyl. piston. And don't forget to use the plug for a non - power brake master cyl.
     
  9. Thanks for posting your diagnosing, and repairs to the system. Glad you got it figured out.
     
  10. V8 Bob
    Joined: Feb 6, 2007
    Posts: 2,966

    V8 Bob
    ALLIANCE MEMBER

    Make sure they are grade 5-8 SS, not the regular grade 2. Torque with lock-tight.
     
    wallster and Boneyard51 like this.
  11. V8 Bob
    Joined: Feb 6, 2007
    Posts: 2,966

    V8 Bob
    ALLIANCE MEMBER

    The booster push rod should normally be around .030".040", and checked with full vacuum applied. Where did you read .0010" to .0015"???
    The use of a M/C bore plug depends on the style of push rod; manual (retained or floating), and power (guided or un-guided). One rule doesn't apply here.
     

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