Brake line size - can it be TOO large? - Page 2 - Hot Rod Forum : Hotrodders Bulletin Board
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  #16 (permalink)  
Old 03-19-2008, 03:12 PM
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Originally Posted by Irelands child
Dewey - you may be in a world of hurt for good brake operation. The larger lines will not allow the full pressure of the MC, designed for 3/16 lines, to reach the wheel cylinders. Take a ferinstance. Your garden hose as attached to the hose bibb at the house can put out a pretty good stream - possible a 50 foot long stream. That hose is probably 5/8". Now, grab a 2" fire hose and screw it on the bibb (with the proper adapters, of course) and turn it on. The water stream is will barely make it out of the end. Same volume of water will exit the hose, but it has now lost its pressure by trying to fill that big hose cavity -

A 10 foot long 3/16" line will have .27 cu in of fluid while 5/16" line will have .75 or 3x the amount of volume then the design calls for - and a MC that's then too small.

Dave W
To answer what I just posted: If you hooked that fire hose to the house fitting AND put the regular garden hose end on the firehose, then the water will shoot just as far, and have the same pressure.

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  #17 (permalink)  
Old 03-20-2008, 02:43 AM
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Originally Posted by Kruzin Karl
Well, if the brake lines are bled properly, and absolutely full of brake fluid, the diameter of the lines (within reason) will have no effect on the pressure at the other end.
I'd like to accent the "within reason" part of this. While its very true that it should have no effect, it really does. The brake lines (even the hard lines) expand as they get pressure. Sometimes in excess of 2000 psi. When dealing with small transfers of volume, a small increase in line size can mean a lot of pedal travel and a totally different brake feel.

Using too small a line will make for slow application as the lines will restrict flow. Using too large a line not only reduces peak pressure handling, it might make a spongy feel, or in extreme cases it might allow more expansion than the MC can supply.
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Old 03-20-2008, 07:29 AM
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Let me insert a bit of "real world" back into this fascinating discussion of the physics involved.

I ended up running all 3/16" line to the rear wheels. For the fronts I used 1/4" line for the first 60" off the MC which then splits at a "T" into two 3/16" lines to each wheel.

It will be a few more months before the car is on the road for brake testing...but I'll try to revive this thread and report back on how well this mix-and-match of line sizes really works under normal driving conditions as well as panic stops.

Now where's that check from Nigeria...I need to order up my new flaring tool.
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Old 03-20-2008, 07:39 AM
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Originally Posted by cboy

I ended up running all 3/16" line to the rear wheels. For the fronts I used 1/4" line for the first 60" off the MC which then splits at a "T" into two 3/16" lines to each wheel.
This should work OK.

Just a thought; there are Master Cylinders that have the connections on both sides. They come in various bore diameters and have plugs for the side not being used.
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Old 03-20-2008, 07:40 AM
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Quote:
Originally Posted by cboy
Let me insert a bit of "real world" back into this fascinating discussion of the physics involved.

I ended up running all 3/16" line to the rear wheels. For the fronts I used 1/4" line for the first 60" off the MC which then splits at a "T" into two 3/16" lines to each wheel.

It will be a few more months before the car is on the road for brake testing...but I'll try to revive this thread and report back on how well this mix-and-match of line sizes really works under normal driving conditions as well as panic stops.

Now where's that check from Nigeria...I need to order up my new flaring tool.

Why do I get the feeling that you've been teasing us out here in the hinterlands

Ya done did it keerect, or there ' bouts

Dave W

Oh, by the way - the check is in the mail - it got sent to me by mistake. It was for $5000, but you'll have to send the balance after you buy the flaring tool back to me.
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  #21 (permalink)  
Old 03-20-2008, 08:51 AM
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Originally Posted by Irelands child
Why do I get the feeling that you've been teasing us out here in the hinterlands
I guess my threads CAN sometimes appear that way. There have been cases where I've finished something (or close to it) and started wondering about the engineering involved so I'll ask a question in retrospect just to double check my own thinking.

Or like this situation, where I had obtained all the parts to do a job and then discovered while doing some follow up measurements, that my sizes might have been off. So I quickly dash off a question to you experts...but continue right along with the fabrication until I get enough responses to make a pretty darned good assessment of whether I'm doing it right or not. In a couple of past instances I've ended up tearing out what I've done because the consensus on the board was that it wasn't right...or might be downright unsafe. But usually, with a slight modification or two, I can finish up the task pretty much according to the majority viewpoint.

I like to keep moving along out in the shop...and in many cases I'm fabricatin' at the same time I'm getting input from you guys as to the pros and cons of a particular task. It will come as no surprise, but quite often when I start in on a new task, I have no idea what I'm doing, no real plan for how I'm going to do it, and no idea what will or won't work. So I'm out in the shop tinkering with different approaches while, at the same time, I'm checking in on my HR.Com threads to see just how some of you folks would tackle the problem.

It just seems to be a process that has worked really well for me in the past. And one of the real joys of the internet is that the HR.Com community is usually right on top of things and within a matter of a few hours, the various opinions and solutions are pretty well articulated, so the fabrication work can continue with hardly a hiccup.
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