Line size for rear disc

Discussion in 'Suspension, Steering, Brake & Wheel Topics' started by newschool72, Aug 6, 2013.

  1. newschool72

    newschool72 Veteran Member

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    Ive heard a couple outfits claim we should run the same size brake lines ,front and to the rear, if using 4 wheel disc. I am looking into a prop valve for the rear brakes and am having a heck of a time finding adapters for the 9/16-18 to 1/4, but I did find a 9/16-18 to 3/16. I have 1/4" line going to the back from the factory ,but am converted to 4 wheel disc. My pedal has been soft sense I put the car together and am now wondering if the bigger line to the rear has been the problem all along.
     
  2. Zspoiler

    Zspoiler Veteran Member

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    look for a proportioning valve for 1979-81 Firebird /Trans Am with 4 wheels disc brakes.
     
  3. BondoSpecial

    BondoSpecial Veteran Member Lifetime Gold Member

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  4. newschool72

    newschool72 Veteran Member

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    My conversion setup came with a prop valve for the setup. Everything came from the same place and is designed to work together, but I didn't go with new line. Im just wandering if the line size should be the same front and rear, if the calipers are identical. I need to install a rear prop valve so I can dial the back brakes down for burnouts at the strip and will change the line to the rear to match the front ,if it will help the pedal feel.
     
  5. John Wright

    John Wright Veteran Member Lifetime Gold Member

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    Don't forget the body drop line that goes from the 1/4" line on the body to the hard lines on the rear axle. Here is what I used....
    [​IMG]
     
  6. BondoSpecial

    BondoSpecial Veteran Member Lifetime Gold Member

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    The single rear line is supposed to be larger than the front lines. 3/16 is the correct size for the front and 1/4 for the rear. The rear has to be larger because it feeds TWO calipers whereas the front 3/16 feeds each front singly.
     
  7. newschool72

    newschool72 Veteran Member

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    That is what I had thought , but Ive seen a couple places where manufacturers recommend same size lines ,if the calipers are the same. I can see where the line size could be different converting from drums to disc brakes. It is over my head to understand because we aren't feeding anything, like a fuel line, but pressurizing something. In fuel lines , the larger line usually has lower pressure, so if there was a parallel ,the smaller line would make more pressure. :confused:
     
  8. BondoSpecial

    BondoSpecial Veteran Member Lifetime Gold Member

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    You are feeding two calipers from one 1/4" line and one from 3/16". That is correct. At the back of the car you have 3/16" lines on the axle housing. You do have 3/16" lines feeding each caliper. You need the 1/4" trunk to feed two 3/16" lines at the back.
     
  9. woody80z28

    woody80z28 Veteran Member Lifetime Gold Member

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    It really doesn't matter either way with disc. I've been told by Tobin at Kore3 and several others that 3/16 throughout is fine. I have a single 3/16 from my master to line lock, 3/16 from line lock to tee, and 3/16 from tee to each caliper. Rear is 3/16 to my prop, and stock 1/4 to rear axle and 3/16 to calipers.
     
  10. newschool72

    newschool72 Veteran Member

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    I was hearing that ,not only is 3/16" fine, but would give a firmer pedal than the 1/4" would. If it doesn't matter ,I wont worry about changing it. I do still have the issue of finding the fittings to work the rear prop valve into my existing brake line. The two valves I am looking at are Willwood. One has 1/8" NPT fittings and the other has 3/16" inverted flair. Other than that ,they are the same. You would think adapting a 1/4" line to an 1/8 NPT or 3/16" inverted wouldn't be hard to find. Try it.:confused:
     

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