Although modern brake systems have reached a high level of sophistication, the hydraulic brake systems present on most vehicles rely on hydraulic pressure being transmitted to the brake calipers through a network of small-bore lines and pipes in order to function properly. As such, brake lines are critical components of all hydraulic brake systems and since the failure of a brake line can have very serious consequences, having the brakes lines on your vehicle inspected regularly and replaced as necessary is well worth the cost and time. In this article, we discuss how brake lines function, the common symptoms of faulty brake lines, a basic outline of what it takes to replace a set of brake lines, and our recommendations for the best replacement brake line brands.
Function Of Brake Lines
Both flexible and solid brake lines form parts of a network of brake lines that transmits hydraulic pressure from the brake master cylinder to the brake calipers. In other words, this means that when pressure is applied to the brake pedal, the pressure (aka line pressure) that is generated in the master cylinder is transmitted throughout the network of brake lines all the way to the brake calipers at the wheels.
Brake line pressures can exceed 2000 psi in some applications under vehicle braking, and since brake fluid is incompressible, the brake lines have to withstand this pressure reliably and effectively each time you depress your brake pedal. This means that when maximum brake pressure is applied, a brake line cannot expand, deform, or change its dimensions in any way that alters the volume of the brake fluid in the network of brake lines. For instance, if a flexible brake line expands under pressure, its volume increases, causing a decrease in the line pressure, which in turn, causes a decrease in braking performance.
Since pressure and volume are directly related in brake systems, the bulk of brake line networks on all vehicles consist of seamless steel piping that is securely attached to the vehicle to prevent damage caused by vibration. All steel brake lines are also joined together with high-pressure steel fittings that are purposely designed not to leak, expand, or deform under pressure. Steel fittings are also used to attach steel brake lines to the master cylinder, ABS controller, and load proportioning valves/mechanisms.
Additionally, short, flexible brake lines are used on the front wheels both to allow the wheels to be steered, and to allow for the vertical movement of the suspension system. On vehicles with independent rear suspension systems, flexible lines are used to allow for the vertical movement of the suspension system.
Generally, steel solid brake lines last quite some time provided that no mechanical damage or corrosion occurs to any part of the line. On the other hand, flexible brake lines (which can include both rubber and steel braided flexible brake lines) tend to wear much more quickly due to the material and the loads they sustain during normal vehicle operation.
Common Symptoms Of Faulty Brake Lines
The symptoms of failed or failing brake lines could include but are not limited to the following:
Low Braking Performance
When a brake line is damaged, either via a leak or material expansion, only limited hydraulic pressure is transmitted to the brake calipers. This reduces braking performance, sometimes so severely that it is hard to bring the vehicle to a stop efficiently. With a big enough leak, the brake pedal may sink to the floor when the brakes are applied. A failing brake line can sometimes be mistaken for air in your braking system (which is solved by bleeding your brakes) in its early stages. If you notice that you have a leak in your brake system, this is a safety emergency and you should not drive your car until it is fixed due to the possibility that your brakes may not work properly.
Low Brake Fluid Levels
Any serious and sudden drop in the level of the brake fluid in the master cylinder reservoir indicates that a leak is present. It should be noted that the normal wear of brake pads and brake shoes over time can also cause a gradual drop in the brake fluid level, however this drop usually occurs over the lifespan of your brake pads and shoes. If you notice that your brake fluid level is low and you are not sure why, it definitely warrants an inspection of your brake lines to ensure that you do not have a leak present.
In some cases, the inner lining of a flexible brake line can fail in such a fashion that the lining prevents depressurization of the hydraulic fluid at the caliper when you release the brake pedal. Since the pressure on the affected caliper cannot be relieved, the caliper remains activated. In this situation, the caliper will drag and overheat, which could cause damage to your brake rotors, calipers, or other nearby components. You may notice a burning smell while driving, which is a good indicator that a caliper is dragging on its brake rotor.
Replacing Brake Lines
While replacing flexible brake lines is usually a fairly simple and straightforward job, it must be noted that the replacement of solid brake lines can be very difficult and challenging even for professional mechanics. Exactly how difficult and challenging this is depends on the make, model, and where in the vehicle the damaged section of steel brake line is located. Since rigid steel brake lines are rarely replaced, this guide will exclusively cover the replacement of flexible brake lines.
Note: The example steps below are intended for general informational purposes solely to help give you an idea of project difficulty and tools required. As all cars are engineered differently, repair procedures and safety hazards vary from vehicle to vehicle. To ensure that you have a vehicle specific repair procedure and an exhaustive list of potential safety hazards, we advise you reference a factory service manual for your vehicle. Similarly, referencing a repair manual such as Chilton or Haynes might serve as a less expensive alternative.
Step 1 – Place the vehicle on a solid and level surface. Using a lug wrench, start by loosening the lug bolts (just enough to break them loose, do not remove them entirely at this time) on the wheels you intend to remove so that you can successfully remove them once the vehicle is in the air. If you don’t loosen your lug bolts slightly, your wheels will spin when you apply torque to try to loosen them once the vehicle is in the air. Loosening them slightly while on the ground avoids this issue.
Next, lift the vehicle off the ground using a floor jack and support it with jack stands, but be sure that the vehicle cannot slip off the jack stands. In this case, a set of car ramps will not be sufficient as you will need to remove your wheels to replace your brake lines. Once the vehicle is in the air, finish loosening your lug bolts and remove your wheels.
Step 2 – On your flexible brake lines, take note that only one end of the brake line typically has a rotatable fitting; disconnect this end of the brake line from the steel line first using a flare nut wrench to make sure you don’t strip the fitting. The other end of the line usually has a fixed fitting that cannot be unscrewed from the caliper unless the flexible line is disconnected from the steel line first. Have an oil drain pan handy to catch the brake fluid that will drain out. Be very careful when handling brake fluid as it can readily damage your car’s paint.
Step 3 – Install the replacement flexible line in the reverse order of removal of the old line. Make sure all connections are tight and torqued appropriately, and that the new line is properly routed and secured. If multiple flexible brake lines are to be replaced, repeat steps 2 & 3 for each brake line.
Step 4 – Once your brake lines are installed, it’s time to replace the lost brake fluid using the correct brake fluid type as outlined in your owner’s manual. Next, it’s time to bleed your brakes. To bleed your brakes, you can use a brake bleeding kit or you can also opt to install one-way brake bleed fittings which can make the job a breeze for one person (when often a brake bleed requires two). Follow the vehicle manufacturer’s recommendations for bleeding your brakes.
Step 5 – Reinstall your wheels, lower the vehicle to the ground, and torque your lug bolts to the appropriate torque using a calibrated torque wrench. Confirm that the vehicle has been reassembled correctly, and double-check the brake fluid level in the reservoir. Top off the level if required, replace the reservoir cap securely, and test drive the vehicle in a safe location to verify that the brake system is fully functional and operating as intended. Troubleshoot as necessary.
Note that flexible brake lines come in two main varieties: rubber and stainless steel braided lines. The brake pedal feel may be slightly different after the brake system had been bled depending on what type you chose to use. Stainless steel lines expand less than plain rubber lines and can thus result in a slightly firmer pedal feel, although this difference is relatively minor.
Best Brake Line Brands
When it comes to choosing the best brake lines for your application, there are tons of options out there to choose from. In order to save you some time, below are some of our favorites to help steer you in the right direction.
AC Delco manufactures and supplies a wide variety of brake products, including both flexible and preformed steel brake lines. Moreover, AC Delco supplies brake components for most passenger vehicles and light trucks on the road today, meaning they are easy to find regardless of what you drive. Overall, their quality is good and their pricing is reasonable which makes them an easy go to. As such, we are confident that they will make a great high value choice for your next brake line swap.
Wilwood’s flexible stainless steel braided brake lines are designed to be replacements for OEM equipment, and usually come with the required fittings and hardware. Although Wilwood is a major supplier to OEM manufacturers, the company also sells performance braking systems including calipers, rotors, and big brake kits for many types of vehicles. Wilwood is a long time favorite for people who place high demands on their braking systems, such as those who race their vehicles at the track or on autocross courses. Overall, Wilwood makes fantastic products. Their price reflects their quality, meaning they aren’t cheap, but we still consider them to be a good value for the money considering the high performance and high quality.