Dismiss Notice

Welcome To CK5!

Registering is free and easy! Hope to see you on the forums soon.

Score a FREE t-shirt and membership sticker when you sign up for a Premium Membership and choose the recurring plan.

Brake line sizing???

Discussion in 'The Garage' started by Smokin'Joe, Sep 12, 2006.

  1. Smokin'Joe

    Smokin'Joe Registered Member

    Joined:
    Jul 27, 2006
    Posts:
    50
    Likes Received:
    0
    Location:
    Butler,Pa
    I'm replacing the hard lines on my truck. All of them for fuel and brakes due to rust. It uses 1/4" line for the brakes. Here is my question: If I replace the 1/4" line for either 5/16" or 3/8" line, will this increase the brake pressure and performace of my truck's stopping ability?
     
  2. loafer

    loafer 1/2 ton status

    Joined:
    Aug 19, 2003
    Posts:
    634
    Likes Received:
    0
    Location:
    Lyman, Maine
    No, it won't do anything but increase the volume of fluid in the brake system. Larger lines will increase the rate at which you can push fluid through the lines, but you don't need this in a brake system because the flowrates are very low.

    The hydraulic force is a function of the area ratio between the the MC and the wheel cylinders/caliper pistons. The rear pressure is also regulated by the combo/proportioniing valve.

    The max pressure can never be higher than what the MC can produce, which is only dependent on how hard you step on the pedal and the area of the MC.

     
  3. ntsqd

    ntsqd 1/2 ton status

    Joined:
    Nov 28, 2002
    Posts:
    3,381
    Likes Received:
    0
    Location:
    So. CA
    And further on this, larger tube sizes at brake pressures expand considerably. So you increase the mushiness of the pedal feel with larger tubing.

    If anything, go with smaller (3/16") tube for the brake system.
     
  4. Smokin'Joe

    Smokin'Joe Registered Member

    Joined:
    Jul 27, 2006
    Posts:
    50
    Likes Received:
    0
    Location:
    Butler,Pa
    Thanks for the info.
     
  5. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

    Joined:
    Dec 14, 2001
    Posts:
    22,060
    Likes Received:
    69
    Location:
    Pleasanton, CA.
    Dude, are you for real? You argue my point of using braided flex hose for the whole rig with you saying it won't make the pedal mushy then here you tell this guy that using larger steel line will increase the mushiness of the pedal feel with the larger line. :surepal:

    Just so he and anyone else can see what i'm talking about here is the link to the other post. http://coloradok5.com/forums/showthread.php?t=184290
     
  6. ntsqd

    ntsqd 1/2 ton status

    Joined:
    Nov 28, 2002
    Posts:
    3,381
    Likes Received:
    0
    Location:
    So. CA
    Not only am I very real, I worked as an R&D Engineer for Wilwood and I have worked on (as in been PAID to) race cars for nearly 15 years. That in addition to working on my own stuff for much longer than that.

    I take it you think I'm contradicting myself? I am not, they are totally different design considerations.
    Have you ever used larger tube or hose? Have you ever done the calc which shows how much the increased diameter increases the surface area? The difference btwn 3/16 tube inside surface area and 1/4 tube inside surface area is a lot larger than you'd think. Over a 12" span the difference is ~2.4 square inches. At a service max of 1200 psi that's a lot of force.
    Since it's pressure over area, and ALL of the area inside is subject to the pressure, and there is no such thing as a perfectly rigid tube, it all expands under pressure. The larger the surface area, the more the tube or hose will expand, which results in a mushy pedal. If we could use -2 (1/8") tubing or hose as a way of reducing the expansion under pressure we would. The problem with -2 is that it won't flow enough volume for a brake system to properly function.

    Braided hose happens to expand nearly the same amount as steel tubing when under equal pressure. Which is to say not very much. Not nearly what the OE hose does under the same pressure. Those are not even close to the same as steel tubing. Put your hand on one and have someone stand on the brake pedal some time. Then do the same with a braided SS hose.
    This lack of large expansion in braided SS hose is why you CAN use it to do a complete brake plumbing job, assuming that you can afford to do so.

    Now if you use -4 (1/4") hose instead of the recommended -3 (3/16") hose then you will have a mushy pedal.
     
  7. Smokin'Joe

    Smokin'Joe Registered Member

    Joined:
    Jul 27, 2006
    Posts:
    50
    Likes Received:
    0
    Location:
    Butler,Pa
    When you talk about flexable line, go with the ss braided line, especialy when you want to increase length, or performance. I know this. It will hurt my wallet, when my truck gets lifted, but is being figured into the cost. My question was about the hard line. Since it needed replaced, I wanted to know if this simple change would do anything. My thinking would've made it worse... ....I want to make my truck better. Thank you for teaching me something.
     

Share This Page