How Brake Lines Work

Does your car have the braking power it needs to make a panic stop?­ See more pictures of brakes.
©­iStockphoto/Mark Atkins


It's happened to every driver at some point. One moment, you're cruising along without a care in the world. You're simply making your way from point A to point B and enjoying the relaxing ride in between. Then it happens: Without warning, there's something in the road ahead. You need to stop, and you need to do it now.


Having to slam on the brakes is a high-drama event that puts the spotlight on your car's braking system. Car brakes rarely get much attention -- that is, until there's an emergency. Then the system that stop-and-go commuters love to hate is on center stage. But how do brakes translate the pressure of your foot on the brake pedal into stopping power?


Arguably, one of the most important brake parts in t­urning pedal action into stopping power is a vehicle's brake lines. Most cars and light trucks have hydraulic braking systems. That means they use fluid to transfer the braking power from your foot to the brakes. In extremely basic terms, here's how a typical disc brake system operates: The fluid is stored in the master cylinder. When the brake pedal is applied, it moves fluid from the master cylinder to the brake calipers, forcing them to clamp down on the brake rotors to slow the car. That fluid is carried through the brake lines, making them a rather critical brake part. If your brake lines don't work, your brakes won't work and you (and your car) will be in a heap of trouble.

In this article, we're going to learn how brake lines work. We'll check out the tools you'll need to repair and replace them, how the lines are threaded through the car and learn about several different materials that brake lines can be made out of. We'll even learn about motorcycle brake lines. But first, let's investigate the tools you should have if you plan to do a little brake line work.


Brake Line Tools

A good set of wrenches is essential for most basic brake line repair.­
©­iStockphoto/­Jan Paul Schrage


Because brake lines carry brake fluid from the master cylinder to various other brake parts, it's important to keep them in good repair. Brake lines should never look frayed, cracked, brittle or corroded. Sometimes brake lines can become worn from rubbing against metal parts of the car (or even another brake part) so pay particular attention to the areas of the line that come in contact with other components. Any leaks should be dealt with immediately -- before the car is driven. If you can't fix the leak on your own and without driving the car, you should have the car towed to a licensed repair shop. Malfunctioning brake lines are nothing to fool around with.


Brake line tools are generally easy to find. In fact, you may already have one of the essential tools required for a brake line repair in your tool box. For basic brake line work, one of the tools you'll need is a set of wrenches. Actually, you'll need two wrenches to replace a brake line. That's because most brake line connections use a hexagonal fitting on each side. You'll need to loosen (and tighten) both of these fittings at the same time -- therefore, you'll need two wrenches.

A tube cutter is another handy brake line tool. If you have a small tube cutter, you can buy metal brake lines and cut them down to the size you need. A tube cutter quickly and evenly cuts through the line, making the cut more exact than it would be if you were using say, a hacksaw. It also keeps the end of the cut clean, with minimal fraying. If there is some fraying or jagged material on the edge of the new cut, a small metal file can easily smooth it out.

If you're doing more complicated work on your brake lines, like flaring -- which we'll discuss on the next page -- you'll need more tools. Read the next page to learn what flaring your brake lines means, why it's done and the tools you'll need to do it.


Brake Line Flaring

­Brake line flaring is a process that adds a flare to the end of the brake line to ensure a leak-proof connection. You can think of a brake line flare as similar to the flare at the bottom of a pair of jeans. Flaring makes the tubing wider at the end. Because the tubing is wider at this point, the connection can slip in deeper and more easily. This is just one more way to guard against leaks.

Most of the brake lines you buy at an auto parts store will already be flared at the ends. However, those brake lines may not be the length you need, so you'll likely have to cut them and then add your own flare, at least on one end.


Brake line flaring tools are available online and at most parts stores where you can purchase other brake parts. In fact, most auto parts stores sell flaring kits that contain everything you'll need. The size of the flare is measured in degrees, and various car manufacturers use different flarings. For safety's sake, it's critical that you get the right size for your car.

Basically, this is the way to flare a brake line: Begin by using a tubing clamp to cut the line to the length you need. Then, before you make the flare, place the brake line fitting (which will eventually connect the line to other parts of the braking system) over the tube. Place the tubing in a clamp to hold it steady. Next, take the flaring tool and insert it into the end of the tube you want flared. The flaring tool looks a little bit like a pitchfork with three prongs. Two prongs attach to the clamp holding the brake line, and the third prong (the one in the middle) actually flares the line. It's mobile; you screw it in and out of the line, which widens it, making the flare.

A proper flare will be even and centered on the opening of the brake fitting. You'll want to take your time with this operation. The quality of the flare determines how well the fitting will connect the brake line to whatever brake part you're attaching it to.

Besides flares, brake lines also have bends -- lots and lots of bends. Keep reading to find out if you have what it takes to bend your own brake lines or if you should opt for the pre-bent variety.


Pre-Bent Brake Lines

In most cases, using pre-bent brake lines can save you a significant amount of time.­


You probably already know that the shortest distance between two points is a straight line. But even though a straight line may be the shortest path, it may not always the best way -- or even possible in some cases. That's especially true when it comes to brake lines.


Let's say there's a straight line distance of just 3 feet (0.9 meters) between two brake parts that you need to connect -- your car's master cylinder and one of the brake calipers. Three feet of brake line is all you need, right? Not so fast -- brake lines need just a little bit of slack so they're somewhat flexible. Think about it: If the brake line can't flex and move along with the car, it will put stress on the connection points and eventually break. Broken brake lines mean that you're not going to be able to stop the next time you apply pressure to the pedal. On the other hand, you don't want so much extra brake line that it's practically dragging the ground.

Bends in the brake lines are important for another reason, too. Logical routing of the brake lines can provide just the right amount of clearance around other engine compartment and chassis components, tucking them neatly out of the way where they won't become damaged.

Of course, it is possible to bend brake lines on your own. All you really need is the proper tube-bending tools; however, figuring out just where to bend the lines and how far to bend them can be rather tricky. It takes a lot of measuring (and patience) to make a brake line accurately connect to a specific brake part.

To save time, a lot of people rely on pre-bent brake lines. These brake lines come pre-measured and pre-bent in all the right places to specifically fit your vehicle. Pre-bent brake lines take a lot of time and hassle out of the installation process because they're already flared and bent for the best possible route through your car. In contrast to straight brake line material, which auto parts stores almost always have in stock, you'll need to special order pre-bent brake lines for your vehicle.

Up next, find out why some drivers might need the added strength of steel brake lines.



Steel Brake Lines

Many off-roaders prefer steel brake lines that resist punctures and swelling.
©­iStockphoto/­Jacom Stephens

Brake lines can be made from a variety of different materials, but one of the most popular materials among off-roaders and performance drivers is steel. There are a couple of advantages to steel:

First, for serious off-road drivers, puncturing a brake line is always a concern. With soft brake lines, a rock or twig could easily make a small puncture in a brake line that could end up being catastrophic. A second advantage is that steel brake lines don't swell the way a flexible line might. With repeated use, a flexible brake line can stretch from the pressure of the fluid running through it. This is called brake line swelling. It may not seem like a big deal, but once the line is stretched, the line pressure lessens, which weakens braking performance. Over time, this decrease in braking performance will only become more if a problem. In a panic situation, you definitely don't want swollen lines. Steel brake lines can't swell and your brakes' performance will remain strong.


Steel brake lines may be strong, but they aren't perfect. They're subject to corrosion and breakage just like other brake parts on your vehicle. Steel lines are also less flexible than other types of brake lines, so their connections to each brake part in the system should be checked more often.

On the next page we'll learn about braided steel lines.


Braided Brake Lines

Not only are braided steel brake lines functional -- they're good-looking, too.
©­iStockphoto/­Aaron Chambers

Braided steel lines are a type of brake part that attempts to remedy some of the problems associated with solid steel brake lines. In a braided steel brake line, a soft brake line is encased in a mesh made of braided strips of steel. You can think of it as a long, thin steel basket. This type of line is sometimes used in household plumbing applications, too. In fact, if you take a look under your kitchen sink, you just may see some braided metal lines.

Because the braided steel mesh has more give than hard steel tubing, the connections for braided brake lines aren't as stressed. At the same time, the braided steel protects the line encased within and prevents swelling. Another plus is that braided steel lines are very attractive. For a lot of hot rodders and classic car buffs who "dress" their car's engine compartment by adding components that look good and well as improve performance, braided steel lines are a must to go with the chrome air filters, valve covers and exhaust headers already in the engine bay.


Because the soft tubing is encased in braided steel, you can't visually inspect the lines for leaks or corrosion. While this is fine for racecars or even off-road vehicles that have these brake parts replaced often, it can be a problem for most street cars. You might not know you have a problem until it's too late. Regular brake system maintenance is critical when you're using braided brake lines.

Motorcycle Brake Lines

Motorcycle riders typically don't have the luxury of a brake proportioning valve. It takes practice to learn how to slow or stop a motorcycle safely.
©­­iStockphoto/Ljupco Smokovski

Motorcycle brak­e lines work in much the same way as car brake lines. They deliver brake fluid under pressure from the master cylinder to the brakes. That's great in theory, but in practice there are a few differences.

For one thing, when you apply the brakes in your car, brake balance is handled by a brake proportioning valve. This valve determines how much hydraulic pressure each axle requires to slow or stop the vehicle safely. On a motorcycle, the rider controls this manually by using a front and a rear brake control. The front brake is operated by the rider's right hand, and the rear brake is operated by the rider's right foot. Riders have to be adept at applying the appropriate amount of pressure to both the front and rear brakes.


Another difference between motorcycle brake lines and car brake lines is actually a cosmetic difference -- brake lines are typically more visible on motorcycles than on cars or trucks. While some custom motorcycle builders hide the brake lines in the motorcycle's frame, most factory bikes have the lines that connect the brake parts running along the frame in plain sight. As a result, a lot of motorcycle riders think just as much about the aesthetics of the lines as they do the function. Braided steel lines are a popular choice, and line connectors -- the places where the brake lines attach to a brake part, like a caliper or the master cylinder -- often have engravings or other designs on them. Motorcycles can also use hard steel lines, just like in a car.

­When most people think of performance, they don't think of their brakes. Keep reading to find out how performance brake lines can take your car to the next level


Performance Brake Lines

It takes high-performance brakes to stop a high-performance car -- and don't forget to upgrade the brake lines, too.
©­­iStockphoto/Ken Babione

If you're increasing your car's engine performance, you'd better look at upgrading the braking performance, too. After all, more engine power equals a need for more stopping power. While high-performance brake parts like multi-piston calipers and ceramic brake pads are popular choices, upgrading your brake lines can improve performance too.

As we mentioned earlier in this article, braided steel lines are a good choice for performance brake lines. They keep braking performance strong because they don't swell like rubber lines can. A swollen line decreases the bake fluid pressure, which will compromise the vehicle's overall braking power. A result of this is diminished brake pedal feel: It will be difficult for the driver to modulate the brakes properly because the pedal will feel squishy or sloppy. Braided steel brake lines also protect against nicks and tears from road debris while maintaining flexibility and a firm grip on the brake part it connects to.


Performance brake lines can also come in different materials, like braided carbon fiber (which is very expensive), Kevlar or even Teflon. While these materials add strength, durability and performance, they also add a significant price increase.

Before you decide to upgrade your brake lines, it may be wise to take a good look at the type of driving you typically do. If you routinely take your car to the racetrack or your truck on off-road adventures an upgrade might be worth it. But if you simply use your vehicle to commute to and from work each day, it's probably better to stick with less expensive lines that are easier to maintain.

Whatever you do, don't stop now. The next page is loaded with lots more information about braking, brake components and other related topics -- just follow the links.



Lots More Information

Related HowStuffWorks Articles
  • Maganate, Steve. "Bending Stainless Steel Tubing -- Bend Your Own Brake Lines." Car Craft Magazine. (Jan. 13, 2009)
  • Persson, Drew. "The Double-Flared Brake Line." (Jan. 13, 2009)
  • Spanky. "Hard Brake Lines At Home." (Jan. 13, 2009)­
  • Stu Olsen's Jeep Site. "Brake Line Flaring." (Jan. 13, 2009)
  • Tobolt, William, et al. The Goodheart-Wilcox Automotive Encyclopedia. The Goodheart-Wilcox Publishing Company. 2006.