This article is one in a series that have been released in conjunction with Wayne's new book, 101 Performance Projects for Your BMW 3 Series. The book contains 272 pages of full color projects detailing everything from performance mods to timing the camshafts. With more than 650+ full-color glossy photos accompanying extensive step-by-step procedures, this book is required reading in any 3 Series owner's collection. The book was released in August 2006, and is available for ordering now. See The Official Book Website for more details.
One of the most popular projects for the BMW 3 Series cars is replacing the flexible brake lines that run from the main chassis of the car to the A-arms and trailer arms. These lines are made out of rubber and, over time, tend to break down and corrode. Carefully inspect the rubber lines every 10,000 miles or so. They can exhibit strange characteristics, such as bubbling and expanding, prior to actually bursting. Failure of these lines is a very bad thing, as you will instantly lose pressure in one-half of your braking system.
Faulty brake lines in the front of your BMW can also cause steering problems when braking. Bad hoses can cause a car to dart from side to side when braking. Bad hoses may also allow pressure to build up in the caliper, but sometimes do not release this pressure properly when the pedal is released.
To replace the lines, first elevate the car (see Project 1). Then remove the wheels from each side of the vehicle for easier access the brake lines. To prevent a large amount of brake fluid from leaking out, push the brake pedal down just to the point of engagement and block it there. You will lose less brake fluid, and less air will enter the system.
Now it's time to disconnect the brake lines. Have paper towels handy, as some brake fluid will leak out of the lines. Brake fluid is perhaps the most dangerous fluid to your car, as any amount spilled on the paint will permanently mar it. If you do get some on the paint, make sure you blot it--don't wipe it off. Your hands may also be contaminated with brake fluid, so don't touch the paint on the car.
The brake lines themselves can be very difficult to remove. The goal of this job is to remove the lines without damaging anything else. In this case, the easiest pieces to damage (besides your paint) are the hard steel brake lines that connect to the flexible rubber lines. These lines have relatively soft fittings on each end and often become deformed and stripped when removed. The key to success is to use a flare-nut wrench. This wrench is designed for jobs like this, in which the fittings are soft and might be heavily corroded. The flared end of the wrench hugs the fitting and prevents it from stripping. Use only this type of wrench, as it is very easy to damage the fittings using a regular crescent wrench.
The fitting is supposed to turn and rotate on the end of the line, but sometimes it becomes too corroded to break free and can get stuck to the hard line. When this happens, the fitting and the line will usually twist together, breaking the line in half. Thus, be careful when removing this fitting to make sure you do not twist the line.
If you do damage the hard line or strip the fitting, the replacement line might be a special-order part that will have to be shipped in from Germany. You can usually find the correct length of line at an auto parts store, but then you would have to bend it into shape--a very difficult process that usually requires a few special tools. The moral of this project, and really this entire book, is that you should use the right tool for the job (in this case, the flare-nut wrench).
After you have disconnected the flexible rubber line from the hard metal line, you can remove it from the car. At the chassis end, the lines are attached using spring clips. Sometimes, depending upon the angle, these clips can be difficult to remove. With a good pair of Vise-Grips, though, they can usually be pulled off the car.
Installation of the new lines is straightforward and easy. Before you attach them, make sure you have the correct ones for your car. There are a few different types, and a few different lengths, so make sure the ones you are putting on match the length and fittings of those you just removed. If the line you install is too short, it may stretch and break when your car goes over a bump.
When it comes to replacing brake lines, many people install braided stainless-steel lines on their cars. Rumor has it the stainless-steel sheath keeps the rubber inner line from expanding under pressure and actually delivers better performance than the standard lines. While this reasoning sounds good at first, it's mostly hype. Stainless-steel braided lines are usually made of the same rubber underneath and are simply protected by the outside sheath. Even if the sheath were tight and strong enough to prevent the lines from expanding, it wouldn't make a difference in braking. If the lines expand a little, the resulting pressure exerted at the caliper will be virtually the same.
Still, I recommend braided stainless-steel lines for your car because the outside sheath does protect the lines from dirt, grime, rocks, small animals, and anything you might run over.
Another point to consider is the label of "DOT" (Department of Transportation) certification. The original rubber lines were required to be certified under a certain set of specifications dictated by the DOT for use on U.S. highways. Often, braided stainless-steel lines are aftermarket components that are not DOT-certified and subsequently are listed "for off-road use only." In reality, these lines are more than adequate for use on your car, and any concern over their use is not really necessary.
However, for those who want to be absolutely sure and certified, there are manufacturers who make DOT-certified stainless steel lines, but they're usually more expensive than the noncertified ones. (Both types are available at PelicanParts.com.)
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Old rubber brake lines are often responsible for poor brake performance. As the car ages, the rubber begins to break down and can clog the lines, restricting the amount of pressure getting to the calipers. Renew the brake lines if they are old or if you are having problems with your brakes. The arrow points to the flexible brake line on the rear of the car that needs to be replaced.
A required tool is the flare-nut wrench that fully wraps around the brake line. If you use a standard wrench, there is a high chance you'll round off the corners, permanently damaging the hard brake lines. These fittings are not very strong, and will become stripped if you don't use a flare-nut wrench. If the fitting becomes stripped, the line needs to be replaced (usually a special-order part from Germany). Also, make sure the fitting is turning (blue arrow), not the line itself (yellow arrow). It is very easy to twist off the ends of the hard lines when the fitting binds.
New stainless-steel lines are identical in size and length to the original ones that shipped with the car. Stainless-steel lines have a protective coating on the outside that prevents the elements from attacking them as easily. However, the stainless-steel sheath doesn't allow you to inspect the rubber inside for significant deterioration. Some of the aftermarket lines are made out of Teflon (or have Teflon components) to increase their durability.