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Old 03-19-2008, 08:57 AM
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Brake line size - can it be TOO large?

I don't have a good double flaring tool so I buy my brake lines pre- made. This has raised a bit of a problem with the sedan delivery build. The MC is off the F-150 donor and the exiting fittings are for 1/4" tube to the front (discs) and 5/16" tube to the rear (drums). After buying the pre-made tube lengths I needed (in those line sizes) I discovered that the actual lines on the old F-150 were all 3/16" - it was just the fitting sizes that were larger. Thus, the only way to match the stock set up now would be to find 1/4" and 5/16" fittings which accommodate 3/16th line and then either invest in the double flaring tool or have the line's flared at a shop.

What I'd RATHER do is simply use the pre-made lines I bought. However, I'm now wondering if the larger diameter lines will have a detrimental effect on brake performance.

BTW - the car is not equipped with power brakes if that makes any difference. I am using a Speedway proportioning valve in the line to the rear brakes. And the lines will be stepped down to 3/16" at the front "T" to each wheel and in the back the line will be stepped down to 3/16" on the exit side of the proportioning valve.
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Old 03-19-2008, 09:04 AM
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The larger the tube the weaker in burst strength (shouldn't make any difference), easier to crush, harder to bend, harder to route, etc. You can get reducing adapters that go in the master and use all 3/16 line. Even using pre-made lines you will end up needing to shorten and flare a few unless you want to zig-zag the tube to shorten it (which looks like a hack job). You can get double flare tools for $20 or get a loaner form autozone.
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Old 03-19-2008, 09:08 AM
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You may be able to use one or more of the following fittings to go from your master cylinder to the 3/8-24 IFF that is used with 3/16 brake line.

Go HERE to see the fittings. I have also posted a photo example below.
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Old 03-19-2008, 09:25 AM
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cboy, line diameter will make no difference. it is pressure, not movement in the system that applies the brakes.

why don't you buy a double flareing tool??? they are cheap. the double flairing tool will allow you to make the right length brake lines as compared to store bought. i just bought 25' of brake line and 5 packs of brake line fittings (25 total,5 per pack) from speedway to build all new brake lines for my vette project. it is way cheaper than store bought brake lines and the result is way better.

i have watched your build and would consider nothing less than building my own brake lines for it. double flaring is easy and also buy some of those tube bender tools (i have 3 different ones) out of the 22 flairs i did only one came out messed up. if you can build a body from scratch you can build your own brake lines...
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Old 03-19-2008, 09:32 AM
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the other guys posted while i was one finger typing. as posted above, use 3/16 line and those 3/8 24 IFF nuts. anything else you need you can find at speedway. you will have mucho fun making brake lines...
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Old 03-19-2008, 09:49 AM
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So you bought 5/16 lines?..I would not use them, for looks, and harder to work with. plus it would look like you don't know what you are doing

If you bought them locally, is there any chance to bring them back for exchange? Most places will bend the rules if you lost the rec't, as long as you are not wanting a cash refund.

Buying adapter fittings to make it all work will cost a bit also, so you should rethink ?
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Old 03-19-2008, 10:09 AM
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It important to replace the original brake line with one of the same size. Installing a larger or smaller diameter line may alter the brake balance in the affected circuit and upset the braking characteristics of the vehicle. If you maintain the same master cylinder bore and increase the diameter of the line, you lose volume/pressure to the circuit. Think of holding your finger over the end of a garden hose. If you increase bore size you LOSE pressure, which can make the brakes 'twitchy' or grab...not good! Stick with the 3/16 line as that is what most US master cylinders are designed for. If running a dual disc setup, remove the residual pressure valves and install an adjustable proportioning valve to the rear circuit.

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Old 03-19-2008, 10:53 AM
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Dewey, Dewey, Dewey ...



http://cgi.ebay.com/ebaymotors/Maste...QQcmdZViewItem


As talented a fabricator as you are ... you definitely NEED a good flaring tool and a few benders.



I have the Mastercool hydraulic flaring tool ... and it is great. At 275 dollars or so it is not inexpensive but it does all kinds of neat flares ...



Imperial ( as well as Rigid ) makes great tubing benders for not a lot of money ...

Deuce ...
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Old 03-19-2008, 11:13 AM
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I use the Mastercool--top photo link--and it is the BOMB! A little pricey, but it will get the flares done faster, cleaner and easier. If you get the large kit (shown) it has dies to make the bubble line flares for late model fuel injection type filters (looks like a 'ring' about an inch back from the end of the line) as well as all the other common ones. Well worth the expense for a quality, investment type tool.
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Old 03-19-2008, 12:18 PM
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Thanks for all the great tips (and the misplaced confidence that I could operate a double flaring tool without any problems). Actually a flaring tool will probably go on my list for NEXT project. But since I already have all the lines for this one, I'm going to try to muddle through.

A number of you recommended against using the 5/16 line and now I totally see why. I could not put a 90* bend into it without a major kink. So that piece of line is now in my "practice" pile.

A number of you also suggested adapter fittings to go from the MC to 3/16. That was my first thought as well. But in my case the MC had to be mounted so close to the valve cover that I can barely get a 90* bend into the gap...much less try to squeeze in an adapter as well. The good news is that with some major coaxing of the line to jog around the engine, I was able to get an adapter and a 3/16 line connected to the rear outlet. Once I had that it was pretty clear sailing to bend my way back to where the proportioning valve will be located. Oh, and I did try at my local Car Quest and Napa stores to find a 90* brass fitting to come off the MC to save space, but they didn't have any and couldn't find anything workable in their catalogs...even if we started piling on adapters. Also tried Speedway without any luck.

While the line to the rear seems to be under control, the outlet to the front brakes is still a challenge, however, since the bend there is even tighter than on the rear outlet. There just does not seem to be enough space to use a reducing fitting and still get the line and nut started. I'll be going at it again this afternoon and my best bet looks like a run of 1/4" line off that front outlet to a "T" and then two 3/16" lines to the front wheels.

Thanks again for all the good tips. And yes, I will be starting a special piggy bank labeled "Flaring Tool". Maybe when I finally get that check from Nigeria I'll be able to afford one just like Deuce's.
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Old 03-19-2008, 01:34 PM
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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
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Old 03-19-2008, 02:26 PM
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At first I agreed with those who said that the line size was going to make a difference. But now that I've thought more about it, I'm not so sure...

The MC is going to displace a certain amount of brake fluid. The key is, all the lines are going to be full of fluid all the way to the calipers before the MC moves.

So, if moving the MC displaces x amount of brake fluid, then x amount of brake fluid is going to be pushed through the lines and into the caliper, regardless of how large or small the lines are in between. If you put a tablespoon of water into a one end of a filled straw, a tablespoon is going to come out the other end. Do the same thing to a 55 gallon drum, and a tablespoon is still going to overflow.

It would be different if we were talking about air, but brake fluid, for all intents and purposes, is not compressible.

If the volume of the lines mattered, then your brakes would get progressively weaker as the piston caliper moved in its bore - the volume of fluid in the bore gets larger as the piston moves the same way a larger brake line has more volume than a smaller one.

The pressure inside the lines is the same pressure as inside the caliper, its the surface area of the caliper (that is movable and thus variable) that determines how much braking power you get from the fluid displaced by the master cylinder.
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Old 03-19-2008, 03:03 PM
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Brake line size - can it be TOO large?

i'm with ckucia
what goes in must come out ,specially if theres no air .
when bending large lines cap one end and pack with sand , use lube on benders .
it will not kink up .
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Old 03-19-2008, 03:06 PM
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Quote:
Originally Posted by ckucia
At first I agreed with those who said that the line size was going to make a difference. But now that I've thought more about it, I'm not so sure...

The MC is going to displace a certain amount of brake fluid. The key is, all the lines are going to be full of fluid all the way to the calipers before the MC moves.

So, if moving the MC displaces x amount of brake fluid, then x amount of brake fluid is going to be pushed through the lines and into the caliper, regardless of how large or small the lines are in between. If you put a tablespoon of water into a one end of a filled straw, a tablespoon is going to come out the other end. Do the same thing to a 55 gallon drum, and a tablespoon is still going to overflow.

It would be different if we were talking about air, but brake fluid, for all intents and purposes, is not compressible.

If the volume of the lines mattered, then your brakes would get progressively weaker as the piston caliper moved in its bore - the volume of fluid in the bore gets larger as the piston moves the same way a larger brake line has more volume than a smaller one.

The pressure inside the lines is the same pressure as inside the caliper, its the surface area of the caliper (that is movable and thus variable) that determines how much braking power you get from the fluid displaced by the master cylinder.

I agree.... you could use 2" line if the wall thickness could handle the PSI. The only thing I can add is that if you used a smaller line than stock, and on something like a slave cylinder that needs more "flow", then a tiny line would slow the reaction.
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Old 03-19-2008, 03:07 PM
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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.
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