Master cylinder size??????

Discussion in 'The whoa and the sway.' started by Bens99gtp, Jun 24, 2019.

  1. Bens99gtp

    Bens99gtp Well-Known Member

    So I want to pole what sizes ppl are using for there master cylinder and what their brake set is.

    We recently swapped from 4 wheel manual drums to 4 wheel disc. Calipers front and rear are willwood dynalight with 1.75 pistons in all 4 holes on all 4 wheels.

    I bought s front kit and put togeter the rear with a weld on bracket and slip over hat and rotor.

    Before buying anything I called willwood several times each speaking to a different tech person to see if I got the same answer each time.........they all told me to use their 15/16 tandem master and since this is a drag car with skinny tires to plumb the primary port to the rear and secondary to the front. As i did. I reused factory lines size, its 3/16" all the way through in front, with the 1/4" running rearward splitting into a 3/16 going to each wheel across the rear axle.

    Bled the master on the car first, till all bubbles stopped both ways. then hooked up to car, started rr,lr,rf,lf. Went through bleeding both sides several times. Had hose on bleeder to be able to see any bubble, after passing more than a quart through the system though we had it well bled out. Rilling in shop dad said he thought it felt ok, pedal was a little lower than b4, I just figured it was going to travel more seeing we had alot more area to fill.

    Today rolled the car outside the shop and down the drive.......I had brakes but not till the very bottom of pedal travel and pedal was very easy to push???????

    I'm using the upper hole in the pedal which should give me a higher ratio. My clevis is only on the master pushrod a few threads to do more I'm going to have to fab up an extension......which wouldnt be hard. I have room to adjust the switch back and get a little longer stroke from the pedal, just not sure how much more stroke is in the master..........I think the said it had a little more than an inch and I would have to wedge myself down there to measure.........but its close to the full travel I had b4 and I even believe the brake switch will work with adjusting it

    I'm wonder if the the 200 dollar master in the size 3 techs from the told me is the wrong size and just flat ass not moving enough volume to fill all 16 pistons????
    Or if somehow there is still air in the system.

    I need to get a pressure gauge on it to find out
    Last edited: Jun 25, 2019
  2. BrianTrick

    BrianTrick Brian Trick

    When going to 4-wheel discs,you need less volume and more pressure,thus the smaller piston in the master cylinder. What do you have for a proportioning valve?
  3. Bens99gtp

    Bens99gtp Well-Known Member

    How I plumbed this with thevwilwood master having a 2:1 volume ratio. The primary has twice the volume as the secondary. I plumbed the primary to my rears, I removed the factory pvalve on the frame, used the same 1/4" line size to rear, and split the rear to a 3/16 each side.

    The front I used the factory 3/16 line size, its tied to secondary port....going through line lock first. The a jegs manual pvalve.

    This is how wildwood said to plumb this. Use the rear tires as primary since I have little skinnys up front.

    I haven't had time to mess with this at all, I think I'm going to get a syringe bleeder and redo the master first and see if any improvement
  4. Bens99gtp

    Bens99gtp Well-Known Member

    After getting a few weeks of track time its seeming the 15/16 master wildwood recommended seems to be working well, I have the adjustable pvalve in the front and I have it set to not reduce anything and all seems to be working well. Pedal travels alot farther than I'm used to, but it works very well, I think when I have time I can extend the pushrod to at least move the pedal up off the floor a little
  5. Skylard

    Skylard Well-Known Member

    For whatever it's worth, i chased a problem and found that even though i bench bled the master, it got air in it.
    the fix was remove the master and get the rear higher than the front, used a stubby screwdriver to press the piston in a few times.
    the air was trapped at the front of the bore.
  6. Bens99gtp

    Bens99gtp Well-Known Member

    I might try this after the season is over, can hurt and think I will have to pull it to build a rod extender as with the cage in the car I dont fit well under the dash being 6'4 350.

    That or some form of pressure or vacuum bleeder
  7. Skylard

    Skylard Well-Known Member

    right i'm 6'4' 225.. not easy.
    does the master point up, in the front?
    if there is any bubble in the line it will find it's way up there,
    i don't think pressure bleeding or vacuum bleed would move it.

    jacking up the rear to level the master might get it, if indeed that is the problem.
    LOL, i own 2 cars and 5 master cylinders.

  8. Bens99gtp

    Bens99gtp Well-Known Member

    It is slightly uphill. And I have the that port going to the rear, as per there subjection to put the primary port going to the rear slicks.

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