Register now to get rid of these ads!

Technical SIZING BRAKE SYSTEM

Discussion in 'The Hokey Ass Message Board' started by Clik, Aug 5, 2021.

  1. Clik
    Joined: Jul 1, 2009
    Posts: 1,965

    Clik
    Member

    All my hard lines are 1/4" but the rubber flex lines are only 1/8".

    Having a 1/4" line being being split with a tee to feed two rear drums through a single 1/8" line doesn't seem right to me but it appears that most flex lines are clearly marked 1/8".

    Thoughts?
     
  2. squirrel
    Joined: Sep 23, 2004
    Posts: 55,941

    squirrel
    Member

    just how fast does that large volume of fluid have to move through that little hole?

    I think you're looking for problems where there are none.
     
  3. Mike VV
    Joined: Sep 28, 2010
    Posts: 3,029

    Mike VV
    Member
    from SoCal

    WHY...would you use 1/4" brake line ?
    That just screws with everything known to making a brake system work well. That's a LOT of additional fluid that the master cylinder has to move for the brakes to work properly.
    Nothing is really designed for 1/4" dia. line. ALL of the master cylinder to caliper or wheel cylinder calculations are designed around...3/16" dia. line.

    3/16" diameter is a MUCH better choice of fluid line diameter.
    Just my, oh so humble thoughts.

    Mike
     
  4. 1/4", 3/8", 1/2".. the diameter doesn't matter. The determining factor is how much VOLUME it takes to stroke the wheel cylinders. The Master cylinder will only stroke that distance (volume), no matter what size line you use. 3/16" is the usual standard however. Like squirrel said, for these sizes, all you're going to see is a difference in velocity.
     
    Elcohaulic, Driver50x, Russco and 5 others like this.

  5. Clik
    Joined: Jul 1, 2009
    Posts: 1,965

    Clik
    Member

    The 1/4" Lines I took off look original and an earlier similar truck I have also had 1/4" lines. I don't know about any of the flex lines since all had been replaced. These are large drums on 3/4 and 1 Ton trucks 1959 and 1965 Chevy.
     
  6. 2OLD2FAST
    Joined: Feb 3, 2010
    Posts: 5,216

    2OLD2FAST
    Member
    from illinois

    IIRC both my OT 1-ton Chevy pickups run 1/4" from the combo valve back to the T at the rear axle then 3/16 to each rear wheel cylinder. I'd just replace what was there ( I've never seen 1/8" brake tube ?)
     
  7. 1/4 , 3/16 once the system is filled and bled your not really moving fluid , but creating pressure .
    The amount the fluid moves is minuscule, but the pressure goes up quickly once you press the brake pedal.

    most systems on newer cars have we 3/16. But a lot of older cars had 1/4”

    I like using 3/16 as I find it easier to work with and parts availability a bit easier.

    but what ever floats your boat. As has been said. Your looking for problems where there are none.
    Go look somewhere else and be done with it.
     
    Driver50x, partssaloon and Ned Ludd like this.
  8. Clik
    Joined: Jul 1, 2009
    Posts: 1,965

    Clik
    Member

    The 1/8" are the flex lines. It's stamped on the hoses 1/8".
     
  9. woodiewagon46
    Joined: Mar 14, 2013
    Posts: 2,269

    woodiewagon46
    Member
    from New York

    Are you sure the ends aren't 1/8" MNTP pipe thread. That may be what they are referring to. Can you post a picture?
     
  10. It makes zero difference what size they are, just stop worrying about it and drive your car.
     
    VANDENPLAS likes this.
  11. gimpyshotrods
    Joined: May 20, 2009
    Posts: 23,264

    gimpyshotrods
    ALLIANCE MEMBER

    That is not how hydraulic systems work.

    If it takes say 1.5-cubic-inch of fluid displacement to fully actuate, it literally makes no difference if the lines are 1/8" hose, or 8" pipe, so long as all of the air has been removed. What is pushed into the system by the master cylinder is what is pushed out at the end of the lines, combined. Line/tube size plays no role here.

    The side-argument of flow rate does not come into play, either, as the system is operated by a person. You cannot operate it fast enough to realize a performance difference if the lines were too small.
     
    Last edited: Aug 6, 2021
  12. gimpyshotrods
    Joined: May 20, 2009
    Posts: 23,264

    gimpyshotrods
    ALLIANCE MEMBER

    Old-school cars had 1/4" brake line. Newer ones 3/16".

    Keep in mind, both of those numbers are tubing measurement standards. In other words, they are outside diameter.

    The inside diameter of each would be that, less twice the wall thickness.

    Your brake hoses are measured with hose measurement standards. In other words inside diameter.

    I cannot find a listing right off, but if memory serves 3/16" brake tubing is about 0.030" wall thickness. Times two that is 0.060"

    Subtract that from 0.188" and you get 0.128" inside diameter. 1/8" is 0.125", assuming the hose manufacturer can hold a zero-tolerance. If not, they differ by 0.003"

    Your car was built the way that it used to be done. That design did not kill anyone.

    Smaller tube and hose are now the standard, and that's not killing anyone, either.
     
    Driver50x, kadillackid and VANDENPLAS like this.
  13. This is the perfect example of why we have so many threads on brakes not working loaded with misinformation. Please don’t give advice if you don’t understand yourself.
     
  14. Budget36
    Joined: Nov 29, 2014
    Posts: 13,174

    Budget36
    Member

    Is the car in question OT? My 67 bug has(although metric) flex hose to a fitted 1/8 th inch metal line to the rear wheel cylinders. I can’t recall what my OT Vette has, and not crawling under it now;)
     
    Guy Patterson likes this.
  15. seb fontana
    Joined: Sep 1, 2005
    Posts: 8,444

    seb fontana
    Member
    from ct

    Take the master cylinder apart and look at the ports in the bores; pretty small, I bet the largest is under 1/8. Very good read by 57 Fargo.
     
    57 Fargo likes this.
  16. BJR
    Joined: Mar 11, 2005
    Posts: 9,816

    BJR
    Member

    Just picture a 1 foot diameter pipe full of liquid, no air what so ever. Now force one gallon of liquid into one end, and one gallon of liquid will come out the other end. Now take a 1/8 " diameter pipe and force 1 gallon of liquid in one end and one gallon will come out the other end. So in this case size doesn't matter! :D
     
  17. Clik
    Joined: Jul 1, 2009
    Posts: 1,965

    Clik
    Member

    Both vehicles mentioned are On-Topic. Chevy 59 and 65 Hot Rod Trucks.
     
  18. Clik
    Joined: Jul 1, 2009
    Posts: 1,965

    Clik
    Member

    The thread size accepts 1/4" IF 7/16"-24
     
  19. Clik
    Joined: Jul 1, 2009
    Posts: 1,965

    Clik
    Member

    But you can push fluid faster at using the same pedal pressure through a 1/4" tube than an 1/8" tube.
     
  20. TrailerTrashToo
    Joined: Jun 20, 2018
    Posts: 1,289

    TrailerTrashToo
    Member

    The fluid only moves a few inches to actuate - and moves a few inches to return. In this instance "size does not matter". If you have ever bled brakes, each stroke produces a relatively small amount of brake fluid.

    EDIT: "size"

    Large bold print does not make does not increase the relevance of your statement.
     
    Driver50x and VANDENPLAS like this.

  21. No you cannot. Your not moving fluid your creating pressure which creates a mechanical action.

    why are you beating this dead horse ?


    0A54B6F9-CA88-40F8-80BE-724E6BB90CA9.gif
     
    gimpyshotrods likes this.
  22. clem
    Joined: Dec 20, 2006
    Posts: 4,188

    clem
    Member

    My brain tells me that you are doing a little of each, - but I have been known to think differently than most………

    maybe you could explain the mechanical action part, with no movement of the fluid ? Thanks !
    .
     
    VANDENPLAS likes this.
  23. What most people miss is it’s a dead end system…there is no “flow” to speak of, less then a tea spoon of fluid moves during a normal brake application. Have some one step on the pedal while you watch the fluid level in the master and get back to us.

    The fluid simply transfers force, that’s it. The input or master cylinder piston exerts a force on the fluid, because there’s no where for it to go it exerts a force on the out put piston or the caliper/wheel cylinder. I think it’s all explained pretty clearly in my thread I linked earlier.
     
  24. I’m REALLY dumbing it down in my last post.

    yes you are moving fluid , but it is moving so little that it almost doesn’t matter ,the brake system is a closed system so no matter how hard you stomp the pedal or how long you keep the pedal down , the distance the fluid moves does not change, only the pressure changes.


    Look at a standard “ closed loop system” like on a forklift. Fluid comes from a tank into a pump, valve then a cylinder to accomplish the “work”

    once the system is full and there is no air, it take very little fluid for that cylinder to creep up off the ground, wether it’s picking up a feather or a 10k roll of steel, the amount of fluid to move that cylinder up 1” will always be the same. Volume of fluid only comes into play when you want to move that cylinder 16’ in the air !!

    I just want to add, even at 16’ the amount of fluid is the same regardless of what’s lifted , a loaf of bread or a fat mother in law, hydraulics don’t care what you think. They just do what they do regardless of beliefs ! Lol
     
    Last edited: Aug 6, 2021
    jimmy six and 57 Fargo like this.
  25. 57 Fargo likes this.

  26. You saying @57Fargo has a big nose?
     
    VANDENPLAS likes this.
  27. Mike VV
    Joined: Sep 28, 2010
    Posts: 3,029

    Mike VV
    Member
    from SoCal

    Yeah...that's why ALL of the factories use 1/2" brake lines..! RIGHT ?
    Fluid IS... moving. Otherwise the wheel cylinder/caliper pistons would not move..!
    If no fluid was moving, we would not need residual valves...RIGHT ? You DO...understand the way that they work...RIGHT ?
    If no fluid was moving, there would be no need for different sized master cylinder pistons...RIGHT ?

    The above (Fargo, and others) comments, is like you don't need "pressure" or "movement" to fire a bullet..!
    Pressure in itself will NOT move anything, unless there is a "movable" object at the other end of the line. JUST like the various pistons MOVING at the four wheels...
    Really dumb thing to say ladies..!

    Mike
     
    Last edited: Aug 7, 2021
  28. Mike ,


    No one is denying there is NO movement, just very little so it does not really come into play.

    fluid does not compress ( well it does but only under extreme pressure which will never be obtained in a brake system.)
    You can think of the fluid like a solid object only transferring force.

    a master cylinder mover quite a bit empty, if you cap the lines and bench bleed it and all the air has been replaced with fluid , I’ll bet it moves less then a 1/2”

    like @gimpyshotrods said, don’t matter if it’s a 3/16 line or a 12” diameter pipe , once the air is out of the system and the system is full , your creating pressure which creates the movement need to actuate what’s at the end of the line.

    on a brake system where both ends are caped and the system is closed the size of the pipe does not matter.

    The sizing of the pistons and rods and either end come into play as that’s what creates the pressure allowing things to move.

    on a loop hydraulic system like in a fork lift or hydraulics where fluid stays in a tank , does “work@ then returns to tank, pipe sizing can come into play if you want that work to happen faster , the fluid needs to move into the cylinder and out in a timely fashion so your not there a month of Sunday’s to get the “work done “

    like @57 Fargo stated, when you bleed your brakes you get a teaspoon possibly at each wheel when bleeding.

    a wheel cylinder moves very little when a brake system is set up properly, a caliper even less .

    and the residual valves, priority valves , check valves etc your talking about are they for either safety sake, to keep thinks in tune or check or to aide in mechanical advantage .


    Sorry bud, your misinformed on this one.

    I’m dumb at most things , but hydraulics I get. Might not be able to explained it the best, but lots of good reading online . Look up pascals law and other folks who “ did the math” on fluid dynamics and hydraulic principal.


    I’m out , before this thread gets locked for internet shenanigans.
     
  29. Like I said, the reason there is so much misinformation…did you have someone step on the brakes while you watch how much the fluid drops?

    it’s pointless to try to convince someone who clearly knows more than the rest of the world.
     
    TrailerTrashToo and VANDENPLAS like this.
  30. Clik
    Joined: Jul 1, 2009
    Posts: 1,965

    Clik
    Member

    If your rear flex hose, which feeds two rear brakes, was only .0125, which is ten times smaller in diameter s 1/8", it would take massive pedal pressure to activate your rear brakes as quickly.
     

Share This Page

Register now to get rid of these ads!

Archive

Copyright © 1995-2021 The Jalopy Journal: Steal our stuff, we'll kick your teeth in. Terms of Service. Privacy Policy.

Atomic Industry
Forum software by XenForo™ ©2010-2014 XenForo Ltd.