Does size REALLY matter???? (Is my tube BIG enough?)

[Fat Hack]

As far as plumbing a disc/drum braking system...does the size of the tubing matter in any way?

I had always believed that brake systems were plumbed with 3/16" steel line, but I had an old Chevy pickup for a while that someone had plumbed with 5/16" line. The brake lines looked HUGE on that truck (1979 GMC 1/2 ton 4x4 to be exact), but it stopped perfect!

I would assume that the size of the tubing really only changes the VOLUME of fluid in the system...you still have a non-compressable fluid actuating the brakes based on input from your foot, right?

Seems to me that 3/16" line would be easier to bend and snake into place, so I intend to use that unless there is some advantage to be had by stepping up to 1/4" or 5/16"???

(I'm not a brake guy for the most part, and this will be my first ever 100% custom plumbed brake system...just want to make sure I do it right!)

[porknbeaner]

Not an expert by no means, but I think you're right about just adding volume.
I've always used 3/16 line unless the master cylinder/brake manufacturer recommended a different size.
I know that some of the older 4 piston discs used bigger lines, but I think that was strictly to compensate for the older less efficient pumps.

[Roothawg]

What size are the fittings on your w/c?
The bigger the tubing the more volume you would have.
Now, since this is a closed loop system pressure shouldn't be any different.....I think??? http://www.jalopyjournal.com/ubbthreads/images/graemlins/confused.gif

[fordiac]

pressure remains constant throughout a fluid.

you are correct, more volume is there.

but that means more moisture can be absorbed into your system. right? boiling point of the brake fluid goes down, corrosionability(TM) of the lines would go up. i would think so anyway.

I would also think that the MC would have to pump more of a volume of fluid to get the correct line pressures. So, would you need a bigger bore on your MC? more travel to the pushrod?

I have no idea though, im just an engineer in training. I havent had Fluid Dynamics yet.


Anyone know how Master cylinder size relates to Wheel Cylinder size, and caliper size?

Why is a proportioning valve needed, why can't they engineer the ratios into the MC?


sorry for stealing the post.

[fordiac]

look what I found in my saved tech files. I dont know where i got it unless it says where its from in the article. I did not write it.
its on my website, if it stops downloading let me know, ill just copy and paste or something.

the basics of automotive brakes (http://joesmanyprojects.freewebspace.com/The%20Basics%20of%20Hydraulic%20Brake%20Systems.do c)

[theodore]

I don't think size would affect the boiling point, if the pressure remains the same so should the boiling point, with a bigger line you might run into problems with seals and peddle feel would be affected to, wouldn't it?

[fordiac]

boiling point in brake fluid is affected by the amount of moisture absorbed into the brake fluid.

everyone is supposed to change out their brake fluid like every year and a half, even on cars that dont move. this is because the fluid always absorbes moisture from the air. this is also why you always need to put the cap back on the brake fluid bottle.

[theodore]

I thought pressure also increased the boiling point? it does in your cooling system, I understand moisture would lower it but I was thinkin in a "new"system there wouldn't be as much(moisture)..

[roadstar]

I have never seen 5/16 lines used for brakes,never!
the old chev you have now had 1/4 lines. Later the used 1/4 in the rear and 3/16 in the front(later 50 early 60's)
By the mid to late 60's it was all 3/16 and had been that way since.

So I recomend using 3/16 lines on the whole system with a duel master cylinder.

[38Chevy454]

Remember how a brake system works: it uses pressure. Sure a small amount of volume is transferred when you apply the pressure, but it is pressure that does the work. If you have such a large area the pressure is acting upon that the tubing ca not transfer fast enough, then you need larger tubing size. But for your car the actual volume of fluid transferred is very small.

So in simple terms it does not matter what the tubing size is. 3/16 will work fine and is easier to run.

[flt-blk]

fordiac
I get a FORBIDEN when I try to access your link.
would you e-mail it to me
zandell@msn.com
Thanks
TZ

[kyle paul]

they only use larger lines on trucks and such . and i belive it only in the front on pickups for the wait transfur .cause the bed is so light they need the braking power in the front and on subs all around because of the wait. more juice more braking i belive

[flamedabone]

38 Chev has it explained pretty well.

The only things I can add are pressure and flow are inversely proportional, pressure is the resistance to flow and flow is dictated by the smallest restriction in the circut. (for example: If you used 3/8 line, but used a 3/8 to 1/4 adapter somwhere in the circut.... you have reduced your flow to what ever that 1/4 fitting will flow. Weakest link in the chain thing...)

Good luck, -Abone.

[Machinos]

Check this out:

http://science.howstuffworks.com/hydraulic1.htm