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.
Replacing your brake pads is one of the easiest jobs to perform on the 911. In general, you should inspect your brake pads about every 10,000 miles, and replace them if the material lining of the pad reaches 2mm (0.08") or less. In reality, most people don't inspect their pads very often, and usually wait until they hear that 'scraping' sound of metal on metal that means the pads are worn out. New pads have about 15mm (0.6") of material on them when installed.
If you indeed get to the point of metal on metal contact, I advise you to replace your pads immediately. Using the brakes during this condition will not only give you inadequate braking, but will also begin to wear grooves in your brake discs. Once the discs are grooved, they are damaged, and there is almost no way to repair them. Resurfacing will sometimes work, but often the groove cut will be deeper than is allowed by the Porsche specifications. The smart thing to do is to replace your pads right away. On some of the later 911s, there are brake pad sensors that indicate to you when the pads are getting low.
Brake pads should only be replaced in pairs: replace both front pads or both rear pads at a time. The same rule applies to the brake discs that should be checked each time you replace your brake pads.
The procedure for replacing pads on all the wheels is basically the same. There are slight configuration differences between front and rear brakes, but in general the procedure for replacement is similar. The first step is to jack up the car and remove the road wheel. This will expose the brake caliper that presses the pads against the disc. Make sure that the parking brake is off when you start to work on the pads.
The pads are held within the caliper by two retaining pins. There are also small retaining clips that hold these two retaining pins in the caliper. Start by removing the small retaining clips, and then tap out the retaining pins using a small screwdriver and a hammer. When the two retaining pins are removed, the cross spring which holds the pads in place will fall out.
Now, the pads can be pried out with a screwdriver. Use the small holes on the pads that normally surround the retaining pin as a leverage point for removing them. They may require some wiggling to remove, as it is sometimes a tight fit. It is important to keep in mind that the caliper piston is also probably pressing against the pads slightly, and will add to the difficulty in removing them.
Once you have the pads removed, inspect the inside of the caliper. You should clean this area with some compressed air and isopropyl alcohol. Make sure that the dust boots and the clamping rings inside the caliper are not ripped or damaged. If they are, then the caliper may need to be rebuilt.
At this point, you should inspect the brake discs carefully. Using a micrometer, take a measurement of the disc thickness. If the disc is worn beyond its specifications, then it's time to replace it along with the one on the other side. See Project 47 for more information.
The installation of the new brake pads is quite easy. You will need to take a small piece of wood or plastic and push the caliper piston back into the caliper. This is because the new pads are going to be quite a bit thicker than the old ones, and the piston is set in the old pad's position. Pry back the piston using the wood, being careful not to use too much force. Using a screwdriver here can accidentally damage the dust boots and seals inside the caliper, and is not recommended. Make sure that you push both pistons (inside and outside) back in the caliper.
Be aware that as you push back the pistons in the calipers, you will cause the level of the brake reservoir to rise. Make sure that you don't have too much fluid in your reservoir. If the level is high, you may have to siphon out a bit from the reservoir to prevent it from overflowing. Also make sure that you have the cap securely fastened to the top of reservoir. Failure to do this may result in brake fluid accidentally getting on your paint.
When the piston is pushed all the way back, you should then be able to insert the pad into the caliper. If you encounter resistance, double check to make sure that the inside of the caliper is clean. You can use a small hammer to tap it in, but don't use too much force. When the pads are in place, insert the retaining pins and spring clip back into place. It's wise to use a new set of pins and clips when replacing your pads. Make sure that you replace the pin retaining clips inside the small holes in the retaining pins.
Tom Woodford of Factory Tour recommends removing and replacing the brake pads one at a time. When the piston is pushed back into the caliper, it will try to push out the piston on the opposite side of the caliper. Leaving the brake pad installed on one side keeps the piston from being pushed out too far.
You also may want to spray the back of the brake pads with some anti-squeal glue. This glue basically keeps the pads and the pistons glued together, and prevents noisy vibration. Anti-squeal pads can also be purchased as sheets that are peeled off and placed on the rear of the pads.
When finished with both sides, press on the brake pedal repeatedly to make sure that the pads and the pistons seat properly. Also make sure that you top off the master cylinder brake fluid reservoir if necessary. Brake pads typically take between 100 and 200 miles to completely break in. It's typical for braking performance to suffer slightly as the pads begin their wear-in period. Make sure that you avoid any heavy braking during this period.
Shown here are some of the parts that you need to replace and refurbish your rear brakes. At the top is a pair of emergency brake shoes. These usually don't need replacing unless someone has been driving great distances with the emergency brake engaged. You need to remove the brake rotor in order to replace these shoes (see Pelican Technical Article: Parking Brake Shoe Replacement). The brake pads featured here are a complete set of rear pads shown with their accompanying retainer kit. The kit includes two new retainer springs and four pins that are used to hold the pads into the caliper.
To remove the old pads, pull out the small pin retainers, and tap out the retaining pins with a screwdriver and a small hammer. They should slide out pretty easily, as there is usually no load on them. If there is much difficulty encountered during the removal process, then tap on the pads slightly to remove pressure from the pins.
Pulling out the pads usually involves the use of a screwdriver for leverage. The pads are loose in the caliper, but it's a pretty tight fit, and there is usually lots of dust and debris in the caliper. Wiggle the pads back and forth in order to pry them free.
When you are ready to install the pads back into the caliper, use a wooden or plastic handle to push back the caliper pistons. Don't use a screwdriver, as you might damage some of the piston seals. Keep your eye on the fluid level in the master cylinder reservoir: it can overflow when you push back on the pistons.
Don't forget to reinstall the small retaining clips for the pad retaining pins. The completed assembly should be carefully tested before you do any performance driving. Brake pads can also take several hundred miles to full break themselves in. Exercise care when driving with brand new brake pads.