Just getting started plumbing brake lines on my AV8 Roadster. I am useing 40 drums front and rear with a 39 master cylinder, Should I use 3/16 or 1/4 inch brake line?
I use to use 1/4" but could never get them bled well.. Switched to 3/16" lines on last 2 projects and had great brakes.. Worked for me...........
I have found more 3/16" than anything else I have worked on. There's lots of fittings for 3/16" and lots of adapters if needed. CN
there is a lot more fittings for 3/16 but you want the LEAST amount of fittings (more fittings more chance of leaking), the wheel cylinders are set-up for 1/4. if your using newer stuff setup for 3/16 then run 3/16 line.
The rule of thumb is to use 3/16" for disc brakes and 1/4" for drum brakes. However, using 3/16" exclusively will give a firm brake pedal feel, while 1/4" makes the pedal feel spongy. Either size will do the job. I am building a 51 Merc custom ch***is with MPC dual power master cylinder and disc/drum brakes. Using only 3/16" SS lines and fittings on this build.
Never heard of either "rule of thumb". If that's so, why did american manufacturers use all 3/16 after 48? As for the spongy thing, no way will 1/4 give you a spongy pedal if bled correctly.
It 's not volume, it's pressure. High volume, low pressure makes very poor brakes. Industry standard is 3/16.
Not for '40s Ford components, Use 1/4", it was stock on those brakes. And brake line size won't affect pedal feel, the MC applies a certain ammount of pressure based on its bore size on the pistons in the wheel cyls regardless of line dia.
My suggestion would be to go to any of the brake parts suppliers website and get your information required from them as to line sizes etc...they are the experts they should be able to guide you properly with proper information from your project. Just my 2 cents worth.
i hate the "volume vs pressure" argument. If the master cylinder pushes 50cc's of fluid into the lines, unless there's air in the system or you've got some highly compressable silicone fluid, you're going to get 50cc's out the other end. regardless of line size. period. Strength vs Pressure. (copy pasted from other source) Tubing Diameter: For light-duty vehicles, systems having discs typically use 3/16-inch line while quad drums often have 1/4-inch line; 3/16 has a higher burst strength to better handle the approximately 1,000-psi pressure required to actuate Disc calipers. (Wheel cylinders for Drum Brakes function more in the 300-psi range.) Metallurgy Brake lines come in two popular materials. OE Tin-Coated Steel: Popular and enduring, these lines are made from low-carbon, continuously welded steel. Some manufacturers such as Cl***ic Tube add galvanizing and an aluminum-epoxy topcoat to deter corrosion. Stainless Steel: Approximately 25 percent more expensive than OE steel, stainless normally outlasts the vehicle. It's a good choice for NMRA mud boggers and Sippy Hole swamp buggies. Stainless has a reputation for being brittle and hard to flare, but many aftermarket suppliers use a softer ASTM grade for easier cutting, bending, and flaring without cracking. (Aluminum is fine for fuel lines, but it doesn't have the burst strength required for braking.) Ferrule Nuts: Choices are OE color-coded steel or 304 stainless, both available in SAE and metric threads. SAE threads were standard on American vehicles from World War II into the '70s. However, metric nuts are common on more-recent vehicles, which tend to use master cylinders and other components sourced from Europe and Asia. Stainless steel nuts are ideal for custom 4x4 hard lines. These nuts won't rust-weld themselves to other components and tend to seat better than oxidation-attracting OE steel. Bending, cutting, and flaring are the three main hard-line maneuvers. Of these, flaring is the most intimidating. SAE 45-Degree Double Flare is standard for most m***-production American automotive applications. It seals in two places: on the outer lip and on the inner 45-degree bevel. Military AN 37-Degree Single Flare usually needs adapters and support sleeves in addition to nuts to mate to automotive components. ISO Bubble Flare is a third style, common on European vehicles Proper flaring is crucial for leak-free sealing. Follow the flaring tool's directions. (Never use pipe dope or Teflon tape on flared brake fittings. For optimal sealing between new line and old components, loosen and retighten the nut several times to create a tight seat.)
I am redoing the brakes on a car. I am taking the 1/4" stuff out and putting in 3/16". I am using adapter nuts that screw into the 1/4 holes but have the center sized for 3/16. I never could get the 1/4 bled right.
For the OP use 1/4" line as that is what the 39/ 40 master cylinder/ wheel cylinder combo was designed for. Line diameter does make a difference in brake system operation, it effects system response time as well as volume and pressure. Unless you are trying to change one of those characteristics, use the same line diameter throughout the brake system. GM used a 3/16 line front, 1/4 line rear combo on full size cars to reduce the tendency for rear wheel lockup. That says a lot about what line diameter can do. Most manufacturers have used 3/16 front and rear, regardless of disc/ drum combo, for the last 50 years or so. An even larger problem w/ most brake system modifications are combos where wheel cylinder/ caliper/ master cylinder piston surface areas are not matched. Changes in piston diameter effect piston travel and apply pressure. Brake systems should be designed around vehicle characteristics such as corner weight. "Volume vs. pressure" needs to be considered regardless of whether you like or dislike the argument. Line diameter should not effect system bleeding. If a system won't bleed properly there is something else going on. Fluids are compressible only under extreme pressures, way higher than any pressure you can generate with a brake system. For automotive purposes all fluids are incompressible, even silicone based fluids. Good luck. Craig
Just a little food for thought. For a given allowable working pressure, as the tube (or pipe size) increases, the wall thickness increases. Given that 3/16 or 1/4 tube is the OD, the increase in wall thickness affects the ID. Point being that 1/4 inch OD tubing will not have a full 1/16 inch larger ID than 3/16 tube. I don't have the actual dimensions but I'd guess the increase in ID might be 1/32 which is pretty insignificant if you were to calculate the difference in actual volume.
I have to ask, WHY, If your running Early Ford Brakes & Master Cylinder, WOULD one even Think of 3/16 Lines when Ford Engineered there brakes to run 1/4 lines ? I have Lincoln Brakes at all 4 corners, Larger Bore Hudson Master Cylinder with Larger Bore Oldsmobile Wheel cylinder on my Sport Coupe with a Desoto Hemi Up front & 1/4 Lines thruout. This car STOP's !!!! Good Pedal, Short Throw !!! Why Would you adapt Down to 3/16 lines .... I Don't Get it
More mis-information here than peanut shells in a pile of elephant ****!! 69 Fury has it correct ,if line is full whatever amount is added at one end, that is what comes out the other. When I was in the HD truck parts world some of the double 12" diaphragm hydro-vacs had max pressures of about 1750 PSI !! What size lines did they use ? 1/4 !! Most spongy pedal issues related to lines is due to routing ie pee/air traps in the line run. Most of the people here need to read up on hydraulic theory .Flame suit on!! Fire away .
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