Disc brake Adjust bike and change brake pads

After the last bike ride over 50 km uphill and downhill with my bike I had to change my front disc brake pads myself. A noticeably worse braking effect of the disc brake made clear without warning. My cyclocross bike Stevens Vapor is known for the relatively bad disc brakes series "Shimano BR-CX77", it's a shame. Actually, I just wanted to adjust the pads after the tour, but somehow this was not without annoying grinding noise. The mechanical disc brake did not work anymore after just 1.000 km > set correctlybecause the small lever on the caliper could be pulled to the stop. Since I had anticipated replacement brake pads here, I decided to change the Resin pads (made of synthetic resin) immediately.

So here's my illustrated instructions for the replacement of mechanical disc brake pads on bicycles, with hydraulic brakes, the exchange is similar, but there are a few peculiarities to note, which I will not go into detail here, because I have no experience. A guide for the conversion > of organic coatings on metal brake pads can be found here.

With mechanical disc brakes, there are two standards that have prevailed:

  • The International Standard "IS" - the frame mounting holes in the caliper are spaced 51 mm apart
  • The post mount system "PM" - the recordings have 74 mm distance (in this example)

As always, I am not responsible for the correctness of the repair instructions shown here, including all consequential damages, but it worked great for me. Please consider: Working on bicycle brakes requires a certain amount of technical experience and a clear mind. With two left hands one goes better to the bicycle dealer, since with improper mounting also on the bicycle danger of life can exist. I have largely followed the instructions of Shimano, which you can download on the Internet for the respective disc brake from the manufacturer and a few simple tricks used in the motorcycle field.

Required tools and material for replacing the disc brake pads on the wheel

  • Small screwdriver
  • Nose pliers for the safety split pin
  • Allen key, torque wrench
  • Set of new rubbers, consisting of two rubbers, a spring and often a sapwood
  • Fat-free cleaning agent such as alcohol, alcohol, cotton swabs, grease-free cleaning cloth, strong rubber band
  • Working time: Brake pad change approx. 20 Min. Disc brake set approx. 5-10 Min. The second time is safe in half the time ...

Change disc brake pads

Disc brake Remove bicycle safety pin

For the first steps, the wheel can still be installed, so you do not have to work on the ground immediately. Of course, maintenance on the brakes will of course work on a bike repair stand. At the usual January temperatures, I prefer the flat as a workshop. When working on bicycle disc brakes, good light is very important, so you can see the gap dimensions well. The brake must of course be cooled before installation, even in winter, it can be hot after downhill driving.

Remove brake pad with a screwdriver

The brake disc should never be touched by hand, as often even small traces of grease reduce the braking power noticeably. Dirty bicycles and brakes please clean before repair eg with detergent and water. After the safety split pin has been pulled out with the needle nose pliers, you can unscrew the retaining bolt with a screwdriver. For this I also had to loosen the black Allen screw of the Bowden cable clamp (bottom of the picture). Some disc brake systems have a disposable safety splint that only 1 x can use. The brake pad replacement kit is often accompanied by a new spring and a split pin.

Removing bicycle disc brake pads

At least now the wheel must be removed. The brake disc should be checked for scoring and wear. The brake calliper can be cleaned well inside with alcohol and cotton swabs after the brake pads have been pulled out. If you want, you can also degrease the brake disc now - very important for newly mounted brake discs! You can clean the brake disc very eg very well with spirit. Also, a brake cleaner from the car needs only heavy dirt on the brake disc is suitable, but this chemical cocktail likes to attack the paint, rubber and all plastic parts. So be careful.

Disc brake pads new and old

With brake cleaner should not be cleaned as possible, the pads, they may be unusable by the absorption of acetone-containing liquid. If the old coverings are to be installed again, it is imperative to adhere to the original installation position again, as each covering has a different contact pattern. The disc brake does not pull properly otherwise. Therefore, used pads must never be exchanged. My brake pads were also gone slightly wrong. On the back you can mark the installation position of each individual covering with a waterproof marker (left and right).

Insert brake padsIf the pads have come into contact with even the smallest amounts of oil or (chain) grease or silicone spray, you almost always have to dispose of them. Some grind the surfaces very easily with fine sandpaper, others lay new brake pads for "outgassing" briefly on a 150 degree hotplate. This should - instead of braking once really hot - help against fading when driving downhill and allow an exact pressure point. I can not comment on that and I strongly advise against it. After cleaning, I pushed both new brake pads together with the spring into the caliper as a sort of "sandwich package".

Brake caliper Shimano BR-CX77 Right in the picture you can see clearly how the spring and the new pads then have to sit in the caliper. I have everything aligned approximately symmetrically. The retaining bolt is screwed back in and secured with the split pin. After that, I used the front wheel again to be able to work more comfortably again. Now you can tighten the Bowden cable again - preferably exactly at the old nip, then the basic setting is the same and you do not squeeze the Bowden cable unnecessarily in a second place. When operating the brake lever, the disc brake should already work. To check the function, it is essential to install BEFORE the wheel with the brake disc. Never operate the brake without brake disc. This is especially true for hydraulic brakes, since you get the pistons then hardly destructively apart. I did not want to write about hydraulic disc brakes, but to avoid bad mistakes in advance:

Common mistakes when working on hydraulic bicycle disc brakes

  • Never turn the bike upside down and apply the brakes, otherwise air bubbles could get into the pipes. The brakes must then be vented.
  • When removing the wheels from the frame spacers between the brake pads must be inserted immediately instead of the brake disc.
  • The pistons have the property of coming out of their own without a brake disc and pressing the pads together. If this happens, do not try to push the pads apart again with a screwdriver. It destroys the porous brake pads with high security. Instead, for example, rather use a soft plastic card. Be patient, do not use force.
  • Never refill brake fluid unless you know exactly which type (DOT or mineral) MUST be filled, otherwise all rubber seals on the brake system may be ruined.

Now the mechanical disc brakes after the brake pad change the wheel still have to be adjusted clean. How this works is described here > second part the repair instructions:

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