Brake line size, what is the best?

Some say run 1/4" line while others say run 3/16". What are most of you running? Any benefit to one over another? My 50 had 1/4" line stock, I have upgrade to 53 brakes and the replacement hoses accept 3/16" line right into them. Do I reduce down to the 3/16" at the master and plumb the car? Or do I try to keep 1/4" and reduce down to 3/16" at the 3 hoses?

 

which ever way is easier.

 

1/4 for drums.... 3/16 for disc! Done.

 

disc brakes like higher pressure with less volume 3/16 line is prefered. drum brakes need more volume and less pressure so 1/4" line is best. Hope that helps,BUCKD

 

no, if that was the case, the reservoir for the drums, in a dual master cylinder, would be larger [more volume].

 

thinking about what you said here made me think, while it makes sense i had to wonder about one thing, regardless of reservoir size when you depress the pedal only the amount of fluid trapped in front of the piston is allowed to pressurize the line so does it really matter how much is in the reservoir? I always thought the reservoir was kinda like a back up in case a leak had started wich would give you a little extra time to pump the brakes and make a safety stop. Am I wrong here?

 

Also the wieght of whats in the res will give you residual pressure wich helps the brakes function as well no? as long as its mounted higher than the brakes themselves and then you need the valves.

 

I have done all mine in 3/16, easier to bend. Most of my cars were the non-traditional four wheel discs though. I am a little funny about stopping.

 

what i was getting at is the line size does not matter, if the master pushes, let's say a 1/2 pint of fluid, into either a 3/16 line or 1/4 line full of fluid you get a 1/2 pint out.

 

Like a couple people have said it doesn't really matter. If you're looking to redo the lines in the car 3/16 is much easier to bend. In your case if all the original line is still good I would just get the adapters so you could tie into the new brake hoses. Your brake system won't notice. Just make sure when you are done to double check for leaks. If no leaks than drive the piss out of it. You should be able to get the adapters in either br*** or steel. Doesn't really matter that way either. If you stop down to a parts store they should be able to know what you would need.

 

I definitly need to brush up on my brake knowledge for sure, Im getting ready to do the whole system on my 54. I have done many and all have worked fine, but really understanding the reasons why they size the lines the way they do I need to figure out. What I have seen in the past is generally the fronts are 3/16 and the rear to the junction on most full size cars and trucks is 1/4. I was under the impression that the rear drums need the lower pressure to keep from locking up thats the reason for the larger line and the fronts had the smaller for the increased pressure for weight distribution during braking. Am I way off? sorry to the op for the hijack! This would be a natural brake bias for a single reservior system.

 

Absolutely correct !!! Use the size line that is the most convenient for the job at hand.

 

3/16 all around is all I ever do. It's whats at each end that counts more.

 

This is a good thread.All i can tell ya on my 59 Dodge Townpanel 1/2 ton, all drums is 1/4 .
On my 74 Dodge d200 3/4 ton truck frame w/disc in front and drums rear is 3/16.

So im thinking there must be a diff if the fac does it ,just my 2 cent. .................YG

 

I believe that you may be over-thinking it. Pressure in a single circuit is the same at any point of measurement, regardless of line size, even if the line size changes.

 

Factory is just saving money, that's all.

 

I use 3/16 for drums and discs.

 

All too confusing now.
1st it was larger for the drums.
Now it is larger for the discs.
Does anyone know the actual truth and why?

 

I ran all 3/16 lines with discs front drums rear and it works perfectly. The more important thing is to make sure that the fluid volume ahead of the piston in your master cylinder is more than that needed to stroke all four wheel cylinders without pumping and without excessive pedal movement. The extra volume in the master is to account for brake shoe/pad wear since as these wear the wheel cylinders move outward and the fluid volume in the system downstream of the master increases. This volume increase is made up from the master reservoir.

 

3/16 to individual wheels, 1/4 from master to "T" in rear, then 3/16 from "T"

 

I always use 3/16(pressure exerted anywhere in a confined incompressible fluid is transmitted equally in all directions throughout the fluid such that the pressure ratio (initial difference) remains the same."<sup id="cite_ref-0" cl***="reference"></sup> The law was established by French mathematician Blaise Pascal.)<sup id="cite_ref-acottLaw_1-0" cl***="reference"></sup>

 

Johnpo is right on the money!!

 

The volume is made by the size of the MC piston and how far it travels, the pressure is made by your foot. The fluid doesn't know what size line it's running through.

 

This is the way I've seen them, and a br*** "T" made for rear end brakes will have the larger fitting in the center for the flex hose and smaller ones out each side for hard lines. Br*** brake line fittings are also different from conventional and aren't flex hoses usually 1/4 while hard line is 3/16? I don't know for certain without going to the garage and looking at some, but I thought that.
Tom S. in Tn.

 

I have done a bunch of these, mostly on the race cars. Yes, the approved technique is 1/4" for volume to drum brakes and 3/16" for pressure to disc - disc brakes need only a teas****ful of fluid transfer.
One time i had only 1/4 tubing layin about so that is what i used for disc brakes and that car was the best/smoothest stopping car i ever did. So that is what i now use. It is easier to transmit volume & pressure thru the bigger line. I know all about dynamic pressure and when you read 1200psi at the master cyl it is also 1200psi at the wheelcyl/pads - the big deal is getting to the 1200psi in the first place and you can get there easier with 1/4" line and fittings.

 

Thanks Guys, Sounds like I will use a combintion of both sizes. Should work fine. Just threw me when my replacement hoses have different inlet thread sizes than the originals.

 

In fluid mechanics when sizing pipes we always look at the pressure drop in the fluid that is attributed to the fluid FLOWING through the line. For a given flow ( in the case of brakes the volume of fluid that you have to push through the line to stroke the wheel cylinders) rate the pressure drop in the line due to friction between the fluid and the line increases as the inside diameter decreases. So if you need to displace say 2 fluid ounces of brake fluid in one second to stroke the wheel cylinders, it will take a bit more pressure in the master cylinder to push the fluid through a 3/16 line than it will through a 1/4 inch line . The only time that the line size difference has any effect is when the pedal is moving from no pedal to hard pedal, the time that the fluid is FLOWING through the lines. Under normal braking when the pedal movement is slow the difference probably isn't even measurable. The only time I could think that there might be a measurable difference would be during a panic stop, but then you would be standing on the brake hard really pressurizing the system anyway , and again the line size probably wouldn't make an noticeible difference.

So after all that , the things to remember are that line size only has an effect when the fluid is FLOWING , and that for a given flow rate the smaller the line id the higher the required pressure at the master cylinder. John

 

If this were true then why did the highly paid engineers at all the major car manufacturers decide to use 3/16 lines for disc and 1/4" for drum in
their cars with disc front and drums rear!!!!