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Brake Line Replacement - Porsche 911 Carrera

Pelican Technical Article:

Brake Line Replacement - Porsche 911 Carrera


4 hours4 hrs






10mm/11mm crescent flare-nut wrench

Applicable Models:

Porsche 996 Carrera models (1999-05)
Porsche 996 Turbo, GT2, GT3 (2001-05)
Porsche 997 Carrera models (2005-12)
Porsche 997 Turbo, GT2, GT3 (2007-13)

Parts Required:

New brake lines or stainless steel brake lines

Hot Tip:

Make sure that corroded rubber from old lines didn't end up in your caliper

Performance Gain:

Better braking performance

Complementary Modification:

Rebuild calipers, replace brake pads, flush brake system, replace master cylinder

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 brake calipers. 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 Porsche 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. To prevent a large amount of brake fluid from leaking out, I recommend pushing the brake pedal down just to the point of engagement and block it there. If you do this, you will lose less brake fluid, and also less air will enter into the system.

Now 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; 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 flare-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 use only 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 might 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. Use a good pair of vise grips to pull them 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. If the line you install is too short, then when your car goes over a bump, it may stretch and break the line.

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 do the standard lines. While this reasoning sounds good at first, it's mostly hype. The stainless steel braided lines are often 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 stock lines already have a metal "spring" that insulates them, so the gain is minimal.

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 U.S. 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. However, 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 (DOT lines are available at

The rubber brake lines are often responsible for poor brake performance.
Figure 1

The 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 red arrow points to the flexible brake line on the front of the car that needs to be replaced. The yellow arrows point to the fittings on the hard brake lines that need to be released using a flare-nut wrench.

A required tool is the flare-nut wrench that fully wraps around the brake line.
Figure 2

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 (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.
Figure 3

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.

Comments and Suggestions:
Juriscon Comments: Thanks Nick. After testing, the master cylinder does not appear to be faulty. I don't have someone to help but I found a method that seems to have worked. It involved attaching a hose to the bleeders one at a timeon the left front and running the hose to the brake fluid reservoir; slowly pump brakes until the line is solid with fluid. There was lots of air that's now gone. Brakes feel okay. Car stops. The new rotors and pads need to be bed. I might do the right front although this method should have taken care of the entire system.
March 14, 2017
  Followup from the Pelican Staff: Thanks for the follow up. We appreciate it.
- Nick at Pelican Parts
Juriscon Comments: Just learned that there may be air in the master cylinder and how to bleed it out. I'll give that a try. I'll also ask fellow Porsche owners at this weekend's Werks Reunion. Thanks!
March 8, 2017
  Followup from the Pelican Staff: Air could cause this issue. You may need to try bleeding it a few more times. Start with a good gravity bleed, then bleed the regular way using an assistant. - Nick at Pelican Parts  
Juriscon Comments: I've gone through 2 cans of fluid; flushed it for a fourth time. Pedal was firm when on the stands. Waited 15 minutes, no leaks; mounted wheels; pressed the brake pedal again and it sunk to the floor. I think I screwed up and blew a seal in the master cylinder.
March 8, 2017
  Followup from the Pelican Staff: To test the master cylinder, pump pedal until hard (engine off), once hard, hold pedal down,. If pedal slowly sinks master cylinder is likely faulty. That is if there are no external leaks. - Nick at Pelican Parts  
Juriscon Comments: I've gotten everything reconnected and checked for leaks. There were a few and I tighten them up. I use the Motive system to bleed my brakes. I went around the car twice just to be sure. There are no leaks. Mounted the wheels and took the car off the stands and engaged the e-brake and then started the engine. I pressed on the brake pedal a few times, however it firmed up a bit and then was no longer firm. I figured the pistons in the calipers needed to set and vacuum needed tot be restored. However, the brake pedal did not firm up. What do you think is the problem? Unfortunately I don't have someone to pump the brake pedal for me.
March 6, 2017
  Followup from the Pelican Staff: You still have air in the system. Try bleeding again, find someone to help. - Nick at Pelican Parts  
Juriscon Comments: I have a 2005 997 with 64,035 miles. It also has 11mm on the body and 10mm from the end of the flexible hose and all around the caliper.

Three nuts were extremely difficult to remove. I used PB and let them soak by wrapping them then applied heat with a MAP torch. The left front on the chassis did not move so I cut the line. It runs a short distance to a monoblock ? and is easy to replace. My flare nut wrench Kobalt did fine on the others.

My advice is if you have a nut that gets damaged, replace it or the line.
February 24, 2017
  Followup from the Pelican Staff: Better to replace the line. - Casey at Pelican Parts  
ScottKer Comments: Thanks for this article, really helpful. Having just done this on my 2003 C4S with 107k miles I have a couple of notes. You have to have a good flare nut wrench because the metal spreaders that create a tight link because the hard lines and the flexible lines make it hard to get a regular wrench on nut. For my car I needed an 10mm on the caliper and an 11mm on the chassis. Weird. Even with heat, penetrating fluid and a flare wrench I still stripped and had to replace, the hard lone going to the caliper. I learned after doing this that the connection to the chassis hardline is a bigger and more accessible nut, so start there, remove the caliper completely with the existing line attached and then on a bench carefully but with a quick jolt, like an impact wrench, unscrew the old line from the caliper hard line.
May 11, 2016
  Followup from the Pelican Staff: Thanks for sharing your installation process and experience. These type of comments add so much to the Pelican tech community.
- Nick at Pelican Parts
Spyder550 Comments: 1. Do you need to bleed the system, or just bleeding the affected line suffices? Seems like the Porsche sequence will help on this. The Porsche factory manual says right rear, left rear, right front, and last left front. In other words, work from the farthest to the closest to the master cylinder.

2. You do not mention that fluid will escape when the line is removed. Will the drain be reduced if the filler cap is left untouched until done? Then refill the reservoir and THEN go to the next wheel? Using a vacuum pump will do the job. Just make sure that the reservoir is full every time you start with a wheel, and that the previous wheel you worked on has been bled.

Any comments from anyone?

September 9, 2014
  Followup from the Pelican Staff: I would bleed the entire vehicle.

When not using a pressure bleeder, I place an upside down bottle of brake fluid in the reservoir, so it doesn't run out. Then suction out any extra fluid when done.- Nick at Pelican Parts

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Page last updated: Thu 3/22/2018 02:37:14 AM