The brake calipers become very hot when they are working, and various stains will adhere to them. Fortunately, cleaning the brake caliper piston is not much more difficult than replacing the brake pads, so it would be better to clean the brake calipers along the way when replacing the brake pads.
Some rubbing alcohol (isopropyl alcohol as a cleaning agent can’t be better), a cotton swab, a flat-blade screwdriver (used for most Shimano brake pads disassembly and assembly), some mineral oil, or DOT5.1 brake fluid (depending on what the brake is Types of brake fluid), the yellow wrench is a handy tool to reset the piston and brake pads, please ignore the bottle of beer!
Pour some isopropyl alcohol into the cap for easy dipping; pour some brake fluid, Shimano red mineral oil, into the other cap.
Working principle of the disc brake piston
Because the brake oil system is under negative pressure, the brake piston will slide over the seal ring when braking and then retract back to its original position. In fact, this statement is only partially correct. The sealing ring of the piston is a square ring instead of an o-ring, and it will actually bend elastically as the piston moves; theoretically, this ingenious design will automatically adjust and reset as the sealing ring wears out, so the sealing ring can also be seen The action is an additional return spring, which makes the brake reset more aggressively and quickly. As the brake pads wear out, the piston will be pushed out deeper than the seal ring to compensate for the space allowance caused by the brake pad wear. And this process will cause more dirt to enter the brake system. That is to say, in theory, we clean the pistons not to allow them to move more freely, but to prevent contaminants from entering the oil system, thereby prolonging the life of the piston seal.
Based on years of brake maintenance experience, after good maintenance and cleaning, the brakes feel significantly lighter and more positive.
This working image from Park Tool shows what happens when you squeeze the brake lever. The piston is white, the black is the seal ring, and the yellow is the oil circuit. The picture on the left shows the normal rotation of the brake disc, while the picture on the right shows the braking state of the brake disc. The oil passage pushes out the piston to clamp the brake pad, and the seal ring undergoes elastic deformation.
Step 1: Remove the brake pads (dual-piston calipers)
Use a flat-blade screwdriver to remove the screws on the top of the brake pad and take out the top brake pad circlip, so that the brake pad can be taken out, and the brake piston can be seen at this time. This XTR is a double piston.
Step 2: Initial scrub
Preliminary scrubbing can prevent dirt from being inadvertently pushed into the piston. Dip a cotton swab with isopropyl alcohol in the cap, and then clean the exposed part of the piston. You can see the cotton swab covered with black dirt.
Step 3: Complete cleaning
After the initial scrubbing is completed, the piston should be further thoroughly cleaned. To do this, please reset the tool carefully not to scratch the piston, or use your fingers to press the piston on one side more carefully to prevent the piston from being pushed out, and at the same time, gently squeeze the brake lever to slowly push out the piston on the other side. , Be careful not to push the piston away from the sealing ring, otherwise, the worst-case is-the piston will come out, the brake fluid will spray all kinds of chaos, you will have to call your technician friend...
Clean the part of the piston that is pushed out with a cotton swab moistened with isopropyl alcohol. Do you see it? There are black stains on the cotton swabs. Keep cleaning until the cotton swabs are no longer so dirty. Then use a cotton swab to soak a small amount of mineral oil (for Shimano or Magura) or Dot 5.1 (for SRAM or Hayes) and apply it to the exposed part of the piston; clean it quickly with a paper towel to ensure that no other liquid gets on the piston. Repeat this step for the other piston.
It is more convenient to use a reset lever or nylon tire lever for assistance.
Step 4: Reset and restore
Gently press the piston back into the sealing ring to reset until the pistons on both sides are flush. Still use the yellow reset wrench, slowly and gently alternate between the two pistons, so that too much force will not be applied; you can also temporarily install a set of old brake pads to protect the pistons, while using a word The screwdriver separates them.
Step 5: Install new brake pads
Install the new brake pads and put them in, and make sure that the piston is fully retracted, and finally install the calipers and wheels. If there is friction between the disc brake pads and the brake pads after the wheels are installed, please repeat the piston reset procedure again.
How to clean the four-piston caliper
When you are dealing with a four-piston caliper, it will be a bit tricky, but only a little bit. A brake exhaust pad is a very useful tool, the steps are the same when cleaning a pair of pistons to prevent the other pair of pistons from moving so that things become simple.
Step 1: Removal of brake pads
Step 2: Preliminary cleaning. This step is the same as the two-piston caliper, although it is more complicated than the two-piston caliper. Use more cotton swabs to do it slowly. (Note: Never put your brake caliper in a vise without a soft pad, even if the soft pad is used, do not hold it too hard)
Step 3: Completely clean. At this point, you need to completely reset the pair of pistons to install the brake exhaust pad. Now you can block one of the remaining pair of pistons, gently squeeze the brake lever, and slowly and carefully push out the piston so that you can clean it. Up. Once it is done, push back the clean piston and repeat the process. Then switch the brake exhaust pad to the clean piston to complete the cleaning of the remaining pair of pistons. Finally, gently press the piston back into place.
The red bottom plate "race" brake pads replaced in the picture are ceramic composite, designed for braking power and quietness. In the future, you may also try HD brake pads with a golden bottom plate for better durability and a "control" feel.
The cleaning process was satisfactory and three cotton swabs were used for each piston.
Maintaining bicycle parts is like most things in life. Once you know the method, roll up your sleeves and work hard, and they will become easy. Over time, this sense of ease seems to increase as I delve deeper into more complex tasks. From now on, maintain your brakes. This is a very satisfying project. Remember to keep the brake pads and pistons clean.