This article is one in a series that have been released in conjunction with Wayne's book, 101 Projects for Your Porsche 911. The book contains 240 pages of full color projects detailing everything from performance mods to changing your brake pads. With more than 650+ full-color glossy photos accompanying extensive step-by-step procedures, this book is required reading in any Porsche 911 owner's collection. See The Official Book Website for more details.
One of the most popular projects for the 911 is the replacement of the flexible brake lines that connect from the main chassis of the car to the A-arms and the trailer arms. These lines are made out of rubber, and have a tendency to break down and corrode over many years. The rubber lines should be carefully inspected every 10,000 miles or so. They can exhibit strange characteristics, such as bubbling and expanding prior to actually bursting. Needless to say, failure of these lines is a very bad thing, as you will instantly lose pressure in one half of your brake system.
Faulty brake lines in the front of your 911 can cause all sorts of steering problems when braking. It is common for bad hoses to cause a car to dart from side to side to when braking. Bad hoses allow pressure to build up in the caliper, but sometimes do not release this pressure properly when the pedal is depressed.
The first step in replacing your lines is to elevate the car. Remove the wheels from each side of the car, as this will make it much easier to access the brake lines. You might want to bleed the entire system of brake fluid before you start disconnecting the lines. Refer to Pelican Technical Article: Bleeding Brakes, Bleeding Porsche Brakes, for more information. If you're not planning on flushing your entire system, Bob Tindel of Pelican Parts recommends pushing the brake pedal down just to the point of engagement, and blocking it there. If you do this, you will lose less brake fluid, and also less air will enter into the system.
Once the brake system is dry, it's time to disconnect the brake lines. Make sure that you have some paper towels handy, as there will be some brake fluid that 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 that you blot it, and don't wipe it off. Be aware that your hands may contain some brake fluid, so don't even touch anything near the paint on the car with your hands.
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 thing to damage (besides your paint) is 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 flared-nut wrench. This wrench is basically designed for jobs like this one where the fittings are soft and might be heavily corroded. The flared-end of the wrench hugs the fitting, and prevents it from stripping. It is very important to only use one of these wrenches, as it is very easy to damage the fittings using a regular crescent wrench.
The other disastrous thing that can happen is that the fitting can get stuck to the rest of the hard line. The fitting is supposed to turn and rotate on the end of the line, but sometimes it becomes too corroded to break free. When this happens, the fitting and the line will usually twist together, and it will break the line in half. Be careful when you are removing this fitting to make sure that you are not twisting the line.
If you do damage the hard line or strip the fitting, then the replacement line is probably going to be a special order part that will have to be shipped in from Germany. You can usually find the correct length line at your local auto parts store, but then you will have to bend it into shape, and most of the time, this is a very difficult process that requires a few special tools. The moral of this story, and this entire book, is that you should use the right tool for the job (the flare-nut wrench).
After you have disconnected the hard metal line, you can now remove the flexible lines from the car. At both ends, the lines are attached using spring clips. Sometimes, depending upon the angle, these clips can be quite difficult to remove. With a good pair of vise grips though, they can usually be pulled off of the car.
Installation of the new lines is straightforward, and the easy part of the job. Before you start attaching the lines, make sure that you have the correct ones for your car. There are a few different types, and a few different lengths, so make sure that the ones that you are putting on are the same length and have the same fittings as the ones that you are removing.
When it comes to replacing brake lines, many people install stainless steel braided lines on their car. The rumor has it that the stainless steel sheath keeps the rubber 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. The 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 enough and strong enough to prevent the lines from expanding, it really wouldn't make a difference in braking. Even if the lines expand a little, the resulting pressure that is exerted at the caliper will be almost the same.
Regardless of the rumor-mill, I will recommend that you place the stainless steel lines on your car because the outside sheath protects the lines from dirt, grime, rocks, small animals, and other things you might run over with your car.
The other thing that might warrant your consideration is the label of DOT (Department of Transportation) certification. With the original rubber lines, they were required to be certified under a certain set of specifications dictated by the DOT for use on US highways. Often, the stainless steel lines are aftermarket components that are not DOT certified, and are subsequently listed for "off road use only." In reality, these lines are more than adequate for use on your car, and any concern over the use of them is not really necessary. For those who want to be absolutely sure and certified, there are manufacturers who will make DOT certified stainless steel lines, but they are usually more expensive than the non-certified ones.
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, leading to very little pressure getting to the calipers. The brake lines should be renewed 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, then there is a high chance of rounding off the corners, and permanently damaging the hard brake lines. These fittings are not very strong, and will become stripped if you don't use one of these wrenches. Once the fitting becomes stripped, the line needs to be replaced (usually a special order part from Germany). Also make sure that the fitting is turning: not the line. 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. The advantage to the stainless steel lines is that they have a protective coating on the outside that prevents the elements from attacking them as easily. There is a downside though. The stainless steel sheath doesn't allow you to inspect the rubber inside to see if there is any significant deterioration. Some of the aftermarket lines are made out of Teflon or have Teflon components to help increase their durability.