Thread: 3/16" vs 1/4" brake line

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Good idea, Hal.

Denny,

The guy at Inline makes good tubes, but he's cluless about hydraulics. 3/16 line simply cannot build more pressure than 1/4 line. No way.

Hmmm.... in my house, I have 65psi at the meter. If I have some lines that are 1/2" dia and some that are 3/8" dia, I should measure a higher pressure on the smaller line according to the posts here..... sorry, it didnt work. Maybe it's because a brake system follows static fluid rules and the garden hose theory follows dynamic fluid flow principles? A brake system is essentially a static flow system, there is no significant fluid flow after the initial piston expansion....when the braking is being done.

Such is why a pressure calculator (such as the one on the Mark Williams site) does not ask for line size, length, material, color, or political alignment.....nor does it ask for the diameter of the wheel cylinder.....it is based upon the master cylinder bore and the applied pedal force to the master cylinder.... lbs force and square inches!

The brake line is only a medium in which to transfer the fluid. If a wheel cylinder requires 1/2 cubic inches of fluid to move a certain distance, the volume and pressure has no bearing on how big or little the transport hose is.....

Denny,

I agree with everything you said about brake pressure and clamping force. It's very concise and understandable.

Robot,

The only issue I have with the gas analagy is that it's an open system. Some Gas enters, some gas leaves - kind of like Thunderdome. Brake systems are closed. Fluid only changes location. None enters, none leaves. Thunderdome after hours.

The best way I have found to look at it is ,the fluid in a brake system is sealed and completely filled with fluid and does not compress...............this makes the fluid basically mechanical {like solid linkage}.
Pressure at one end{master cylinder} is going to be exactly the same at the other end{caliper/wheel cylinder} unless rubber lines are exspanding etc.

A giant piece of line in the middle is disregarded in the system ,if,it reduces back down to the small size before entering the caliper/wheel cylinder.....2 inches of fluid travel in a 3/16 th line will only be approx a 1/4 inch travel in 1 inch line,but will regain 2 inches of travel when that volume is reduced back down to 3/16ths......basically the fluid acts like solid linkage while its contained inside the line.
Thats how it was exsplained to me..I dunno?

As a matter of fact, the mechanical analogy of a hydraulic press is a lever. The same equations apply.

Shawn,

A giant piece of line between the cylinders is ignored even if it doesn't reduce at the wheel cylinder. You could have a 1" line going into the wheel cylinder through a 1" fitting, and the brakes would act the same. A closed system is a closed system. Also, the pressue is always the same everywhere in the system even if rubber lines expand - at least as long as they don't break.

Minor points, but I kind of enjoy these technical discussions.

Originally Posted by Henry Rifle

Minor points, but I kind of enjoy these technical discussions.

Me too... I know I just learned a thing or two ... thanks for getting me back to earth

I know this is a really old thread but it popped up on a Google search. I just want to say to anybody seeing this post, don't be an idiot. LARGER BRAKE LINES REDUCE PRESSURE!!!!!!!!!!!!!!!!!!!!!!!!!! The increase in volume from the enlarged lines will reduce the pressure because the MC now has to move more fluid. When you increase fluid you reduce pressure. So the moron posting on here about how line size doesn't change pressure is a complete tool. Henry Rifle is flat out wrong!!!!!!!!!!!!!!!!!! Ask me how I know? Oh, I work for the largest aftermarket brake company in the county, pretty easy to figure out.

take your i know everything attitude elsewhere . you digging up a 13 year old thread just to insult one of our members makes you a troll .

Originally Posted by Smockdoiley

I know this is a really old thread but it popped up on a Google search. I just want to say to anybody seeing this post, don't be an idiot. LARGER BRAKE LINES REDUCE PRESSURE!!!!!!!!!!!!!!!!!!!!!!!!!! The increase in volume from the enlarged lines will reduce the pressure because the MC now has to move more fluid. When you increase fluid you reduce pressure. So the moron posting on here about how line size doesn't change pressure is a complete tool. Henry Rifle is flat out wrong!!!!!!!!!!!!!!!!!! Ask me how I know? Oh, I work for the largest aftermarket brake company in the county, pretty easy to figure out.

What are you an "engineer"? Take your BS elsewhere snowflake.

Nope, I'm good. I think having accurate information in this post is more important than someone's feelings. He's presenting himself as a know it all and correcting everyone else when he is in fact wrong. Change the mc bore, brake line diameter or braking bore sizes and you affect the pedal feel as well as pressure. To say otherwise is inaccurate information which is a very bad thing when talking about brakes.

I think it's pretty comical to care more about someone's feelings or reputation than the safety of someone who stumbles upon this thread and grabs wrong information. You think just because it was written 13 years ago that it won't be read by someone now? So no, I don't care how old this thread is if Google is still giving it to people. So you'd rather the forum carry incorrect information for an entire generation of hot rodders? Yea, that's really smart. Sure makes you and the forum look great. But hey, you attached your name defending said practices. Good for you. It's called ego, you should check it. Get a lot farther in life.

What you say is only partially true. There will be a momentary increase in psi, but once the pedal stops traveling, the psi remains the same at each end of the line, The smaller line will increase psi during travel only.

Jack (Henry Rifle) hasn't been on here for quite some time, but he was dead nuts accurate in everything he said in 2007, and it's still accurate today. Smockdoiley, it's not a matter of defending a member, it's simply being smart enough to know that what he said is correct.

you `ve been a member for 15 years .. we`re happy you gave this a lot of thought ..