Brake line size?

[QSPres]

Every car is different. Master cylinder, gross weight, rotating weight, etc...

[6'9"Witha69]

You can lead a horse to water . . .

[speED]

According to Pascal's Law: liqiuds under confiinement transmit pressure undiminished. Therefore if we go from a small master piston to a larger caliper piston we increase pressure because of the amount of pressure being exerted on each square inch of the caliper piston. Line size will not change pressure. I think the question is whether or not it changes the rate at which it gets there.

[parsonsj]

I was thinking of ordering a set of the stainless reproductions, but before I did, I wanted to make sure that the stock diameter lines would be sufficient for these new, modern brakes?

I'm going with whatever kit is readily available for my frame...

So why did you waste our time?

jp

[QSPres]

No one forced you to answer........or to keep responding.

Just because I don't accept your answer doesn't mean it was a waste of time to everyone...

[parsonsj]

Line size will not change pressure.

Sorry, but that's just wrong, assuming similar materials and wall thickness. I explained why up above. It may not change it very much (especially at these diameters), but it will change it some.

jp

[QSPres]

According to Pascal's Law: liqiuds under confiinement transmit pressure undiminished. Therefore if we go from a small master piston to a larger caliper piston we increase pressure because of the amount of pressure being exerted on each square inch of the caliper piston. Line size will not change pressure. I think the question is whether or not it changes the rate at which it gets there.

Some of these guys seem to think that the hard steel lines would flex significantly... That would change the pressure. But, lines that are thick enough don't flex that much..

The thing that would most change rate would be the MC, no?

[QSPres]

Sorry, but that's just wrong, assuming similar materials and wall thickness. I explained why up above. It may not change it very much (especially at these diameters), but it will change it some.

jp

Again, you're making the assumption that the wall thickness is not enough... And that's not correct.

[parsonsj]

you're making the assumption that the wall thickness is not enough

All material deforms under a force. It's only a matter of degree.

But just to be sure I'm not misunderstanding: are you saying that there is absolutely no flex (expansion) of the brake line? Not even a little bit?

jp

[QSPres]

Not enough to take up two pages for server space.... If you know what I mean...

[parsonsj]

Not enough to take up two pages for server space.... If you know what I mean...

I don't. Sorry. You've not answered the question.

jp

[BonzoHansen]

So why did you waste our time?

jp

JP, it isn't a waste - I sure got a lot out of this thread. I'm sure others did too. Thanks all-

[parsonsj]

JP, it isn't a waste - I sure got a lot out of this thread. I'm sure others did too.

Cool, thanks.

[QSPres]

I don't. Sorry. You've not answered the question.

jp

Then get used to disapointment I suppose..

[parsonsj]

Then get used to disapointment I suppose..

Well that answers that. We can see the depth of knowledge of materials and their mechanical properties that you bring to the table. Nicely done.

jp

[QSPres]

Thanks. Feel free to move on from my thread any time.

[Taylor1969]

Get with The Right Stuff http://www.rightstuffdetailing.com/
they built me lines to my exact specifications (shorten axle lines by 3", 3/16 throughout, stainless, etc) and they'll even put on any fitting/flare (metric/standard, mix, etc.) without question.

BTW... My setup is as follows:

C5 Calipers Front
LS1 Rear
3/16 stainless Hard lines
FlexKore Stainless soft lines
SSBC Propblock
Custom Hydroboost
LS1 Master

BTW - thanks to ATS for the line size reccommendations (and spindles), Tobin for the lines and calipers, and CarlC for all of his great hydroboost information

Once my hydroboost is complete I plan to start selling some kits if anyone is interested.

Thanks,
Chris

I am putting it all together now and I expect it to perform very well

[QSPres]

Cool. What did they charge for the lines they made you?

[parsonsj]

Thanks. Feel free to move on from my thread any time.

QSPres is Goatman who was banned earlier this summer.

jp

[chicane67]

So... why did PBR and GM build the questioned brake system with 3/16" line ?? Because that is what the Engineers calculated for safe, effective and correct braking pressures for the intended system. The summatation of their calculations gave them an ideal pressure to volume ratio, for this specific braking system. Basically, they did the math and they did it correctly. There is your answer. Yes... you could run the factory 3/16" front and 1/4" rear. But, if you wanted to maintain the pressure to volume ratio calculation (for the intended system) that a few Engineers spent the time to figure out... 3/16" front and rear would be the way to go. That way, you are starting out with a KNOWN and working pressure to volume system ratio without having to reinvent the wheel or having to modify it... which in lame mans terms... means spending more money to get it closer to the "Engineered pressure to volume ratio."

speED stated a singular law derived from the mind of Pascal. It is also stated in Bernoulli's efforts and to be more specific, the divergent/convergent ducting principals (the venturi)... where going from a larger size to a smaller line size will increase velocity and reduce pressure. And on the reverse... going from a smaller line size to a larger, it will decrease velocity and increase pressure. Master sizing has a larger effect over brake system pressure... but does the line sizing ??

Since liquids don't compress, and any pressure created in the master cylider is also present in the caliper, how can the diameter of the brake line make any difference in braking power? Good question! Assuming the two brake lines have the same expansion percentage, there is no difference in the pressure deliverered by a 3/16" line over a 1/4" line... but there is a difference in volume. It simply takes a larger volume of fluid to move a larger piston... no matter what the line pressure.

Most master cylinders have bore diameters between 7/8" to 1 1/8". The 3/16" line volume is near half that of a 1/4" line, restricting the flow from the master cylinder, making the pedal feel "tighter", and giving a different "feel" at the pedal. This is why some people like the 3/16" brake lines better than 1/4" rear brake lines. Braking power is not increased, but the perception of the braking power does change.

3/16" lines flow less volume to allow a fast retraction of the pads from the rotors. This means that when you release the brake pressure, the extra restriction of a line size smaller than 3/16" line keeps your pads rubbing against the rotors far longer than it would with 3/16" to 1/4" brake lines. There are no "return springs" in your calipers. The pads retract only as the fluid flows back out of the caliper, through the brake lines, and back into the master cylinder. Slower pad retraction caused by a line size smaller than 3/16" can cause your brakes to stay much hotter, inducing pad glazing, pad backing plate warping, brake fade and premature fluid break down in extreme cases. But since we are focusing on the rear line specifically... what I just stated has less of an impact from 3/16" or larger line sizing.

About the whole material expansion issue... the real trick is controlling the expansion, not eliminating it. If you could totally eliminate brake line expansion using a steel tube from your master cylinder to the caliper, you would have brakes that were so sensitive and grabby that manufacturers would have to re-think brake pad compounds and master cylinder designs. You need a small amount of expansion (about 4%) for brakes to have the proper "feel" that is critically important to racers. Too much expansion and you loose braking power and feel, too little expansion and your brakes will be too sensitive to have good control. The reality is that most brake lines, even aftermarket "performance" lines, simply have too much expansion. The stock rubber lines are fiber reinforced, but do not do a wonderful job of controlling expansion, and when they get hot, the rubber become softer, allowing more expansion.

And also to quote another brake guru... "When upgrading to disc brakes front or rear, the car should be upgraded to 3/16" brake line. This size line builds up more pressure and gives a much better pedal feel. 3/16" line is commonly used for disc brakes while 1/4" line is used on full drum brake cars."

~Nobody's Fool, Jack