CHANGING DISC BRAKE PADS: THE WHEN AND HOW

Sooner or later most of us will make the transition to disc brakes. The biggest worry for many that are new to the modern binders is simple maintenance of the brake pads. It’s a relatively easy to learn process that can save you money in the long haul.

The material on the pads is so much thinner than those from rim brakes that it can be hard to tell how much life is left. On average, each disc brake pad will have about 2mm of material when new.

The pads will also have a return spring that helps assist in centering and the return movement of the pad. This is about 0.5mm thick and a good indicator of pad wear. This means you don’t want to wear the pads past about 0.6mm or about 70 percent. You can normally shine a light into the brake caliper and visually see how much pad is left, but removing the wheel can make it easier.

Another thing to check is that pad wear is even on each side and front to back. Many times, a caliper or its mounting points might not be perfectly aligned, and this can cause uneven and accelerated wear.

In most cases, the hydraulic system is only made to operate correctly with as little as 0.4mm of pad material left per side. Then the lever and caliper pistons will no longer be able to actuate the pad the appropriate distance. This will result in a lever that will hit the bar before the pads are able to completely contact the rotor.

Another common issue with pads is that they get contaminated and lose their ability to create friction. This will feel like the brakes are moving correctly, but no matter how much pressure you apply to the brake lever, it is not enough to stop. Sometimes this can be from road grime (and can be sanded off with sandpaper), and the most likely culprit can be from using incorrect cleaners when washing a bike. It is very difficult to recover a contaminated pad, and the usual result is them needing to be replaced.

PICKING THE CORRECT REPLACEMENT PAD

Choosing the correct pad for your system could be the hardest part of the whole job. Each brand’s calipers have a specific shape, which means there are a lot of pads on the market. Additionally, there are usually a few options in the type of brake-pad material as well as backplate.

Shimano offers two brake-material compounds—resin and metallic. Resin is the most common for road applications and is quieter, while also resulting in less brake dust. Metallic is more common in off-road applications and is more abrasive, which can lead to more noise. Metallic pads are also not compatible with all rotors, so check the specifications of the rotor you are using.

Shimano offers backing plates in alloy and stainless steel, as well as with or without cooling fins for dissipating heat. Like Shimano, SRAM also offers two braking materials—organic and sintered. They also come in alloy or steel backing. Organic pads are quieter with better initial bite and modulation, while sintered are more consistent under heavy braking or wet conditions.

Campagnolo currently only offers one style of pad that is an organic compound with steel backing. They have a built-in wear indicator, and instead of a return spring, the brake-pad return is accomplished by a magnetic system in the caliper piston. Also unique to Campagnolo is a special metal plate positioned between the pad and the caliper piston that is said to cushion the vibrations during braking.

There are lots of aftermarket brands—Galfer, Swissstop, Kool-Stop, Jagwire, Alligator and more—offering pads that fit all the systems. Some claim better stopping in specific conditions, or lighter weight, while others just offer an economic price point.

HOW TO CHANGE THE PADS

1. Changing pads is fairly easy and starts with removing the wheel from the bicycle. Be sure that when the wheels are removed that you do not actuate the brakes. If it does happen, this could result in the extension of a caliper piston past its designed functioning limit and can cause damage to piston seals.

2. Next, you need to manually retract the caliper pistons, as they have most likely auto-adjusted over time to compensate for the wear on the pad. You can do this with the old pads in or out and would be determined by the tool you are using.

If all I have is a flathead screwdriver I leave the pads in and leverage the screwdriver against the worn pad material and backing plate for each side. This can damage the remaining pad material, so make sure you have
a replacement.

The preferred method is to use a plastic tire lever against the piston after you remove the pads. When doing either method, ensure the caliper is at the lowest point in the braking system.

3. Remove the brake pads from the caliper. This will start with the security pin that will vary in design on each system. These normally go through the backing plate of each pad and either thread to the caliper or have some sort of locking clip that secures the pads from falling out of the caliper body. Then simply pull the pads out of the caliper.

Remember, if you didn’t already push the caliper pistons back into the caliper manually, this is the time to do it with something less abrasive like a plastic tire lever. You don’t want to damage the caliper piston or seal.

4. Clean the caliper and surrounding area so it is free of dirt, debris and brake dust. Isopropyl alcohol works here, but soapy water works too.

5. Now it is time to install new pads. It is important that you do not touch the pad compound, as this could contaminate them. For Shimano and SRAM pads, place the retraction spring between the pads, then with two fingers pinch the outside of each backing plate and slide them into the caliper as one complete unit. Do not try to insert them one at a time. For Campy, there is no spring, so place the pads together, compound against compound, and slide it in. The magnetic system will latch to the pad when it is in place.

For all the systems, check the backing plate for markings to ensure you have the correct pad on the correct side of the caliper. Most pads will not fit correctly if installed backwards. Reinstall the security pin, and if your new pads came with new hardware, use it as long as it matches what you removed.

Some Shimano pads come with a split pin instead of the circlip. I prefer the circlip, but if you must use the split pin, make sure to bend the slightly longer tail so it doesn’t slide out.

6. Now you need to reinstall the wheel and ensure the caliper with the new pads is centered with an even gap on each side. Now pump the lever a few times. This will reset the pads to the correct distance from the rotor.

7. The last step is the most important and most overlooked. Before you go out and test your new pads, you need to perform a bed-in procedure to gain optimal performance. Accelerate the bike to a moderate speed, and then firmly apply the brakes until you are at walking speed. Try and remain seated while applying the brakes. Repeat this process a few times.

Then accelerate the bike to a faster speed and apply the brakes until you are at walking speed. Repeat this process a few more  times. It’s important that during this process you never come to a complete stop or lock up the wheels at any point. Coming to a complete stop causes a build-up of pad material in one spot that can lead to pulsing and noisy brakes.