[DIY Classroom]It is very important to clean the brake calipers regularly!

Disc brakes are currently the standard equipment of mainstream motorcycles. The principle is to use the lever to squeeze the brake fluid to push the piston to transmit braking force. According to the condition of the calipers, if the motorcycle is parked for a long time, be sure to check it before riding again.

Why is the thickness of the inspection sheet important?

▲After KAWASAKI ZEPHYR has been stored for several years without riding, the front brake is stuck in a stiff state after the brake lever is tightened. The reason for the brake jam is not only the caliper sealing problem mentioned here, but also the caliper This is caused by the sticking of the deposit on the pin and the piston of the master cylinder.

As the brake shoes wear, the gap between the lever and the pedal will increase in drum brakes. This is because the parts in the brake drum will not automatically change position as the brake shoes wear, but disc brakes will not follow To make the piece wear and change the lever or pedal gap.

The reason is that with the wear of the incoming disc, the caliper piston will gradually push the disc inward. If the disc is worn by 1mm, the piston will push inward by 1mm. If the disc is worn by 5mm, the piston will protrude and push 5mm. Position, operated by the principle of lever, the piston will protrude and push to make the disc squeeze the disc.

So you don’t need to adjust the lever gap of the disc brake, but if you don’t check the wear of the disc, you may find that the brake pad of the disc is exhausted, causing the disc to be squeezed by the metal bottom plate of the disc. Hmm… Since the metal bottom plate is an iron material harder than the disc, the surface of the disc will be scratched and the disc must be replaced.

Even if the tie rod gap does not change, if the piece is worn and the caliper piston is pushed out, the brake oil in the oil pot of the brake master cylinder will drop. Usually the oil tank has a liquid level inspection window, you can check the amount of liquid, so please be sure to check the amount of brake oil here and the amount of remaining pads, this is very important.

◆ Webike-Moto Department Store’s Lai Ling Film Product Page

Even if the disc is worn, the operating feel of the disc brake will not change.
From the oil level of the brake oil pot, you can see the wear of the pad.
You can directly use a caliper to measure the remaining amount of the piece.

Since the piston is sealed, the gap between the pieces will not change

▲If the caliper piston is difficult to remove, please use hydraulic pressure to push it out before removing the brake hose. If the piston cannot be pushed out normally, soak it in hot water or heat it with a hot air gun to let the brake fluid be heated and softened.

In a disc brake, the caliper piston is pushed inward as the disc wears, and the piston seal and dust seal play an important role. These are O-rings with a square cross-section, which are installed inside the caliper while in close contact with the caliper piston.

When the brake lever is held, the fluid pressure of the brake fluid pushes the piston out, and at the same time, the elastic piston seal pulls the piston in the extending direction. Then when the tie rod is loosened, the deformed seal will force the piston back to complete the return work. This is the most important operation of a disc brake, called return.

The piston is pulled back by returning, but not mechanically. Therefore, if the piece is worn beyond the elastic deformation limit of the piston seal, the base point and starting position of the piston will change, and then the piston will protrude again. Then return to the place.

Through the return work of the elastic deformation of the piston seal, the disc brake does not need to be manually adjusted, so that the gap between the disc and the disc will not change, and the gap between the tie rod and the pedal will not change. The same working principle applies to small-displacement motorcycles or single-piston calipers and six-piston calipers suitable for large-displacement motorcycles.


There are two sealing rings in the caliper.
Sealing and restoring the piston is the most important.

Deterioration of seals and changes in brake oil hinder piston operation

▲If you have a compressor, you can use high-pressure air to remove the piston, but if you fix the air gun to the oil inlet of the caliper and blow air, the piston will pop out, which is very dangerous. Separate the air gun from the caliper, blow little by little, and then push out the piston little by little. If the pushing effect is not good, connect the brake hose and push it out hydraulically.

Brake fluid is a kind of hydraulic fluid used in disc brakes. It is hygroscopic. It will gradually deteriorate in wet and rainy weather, and will evolve into another type of deterioration if it encounters a boiling point. Due to the structure of the piston itself and the wear of the brake pads, the brake oil is likely to adhere to the outside of the piston and seep.

If the degraded brake oil is further deteriorated, it will solidify into deposits and attach to the seal groove of the oil seal or caliper, resulting in a decrease in the elasticity of the rubber and causing additional friction between the seal and the piston.

If the function of the piston seal deteriorates, the movement of the piston will deteriorate. If you grab the lever, the piston is pushed out by the fluid pressure of the brake fluid, and the disc will be squeezed by the piston pushed by the piston. If the piston fails to fully return when the tie rod is released, the incoming film will be dragged to the disc.

In addition, deposits generated in the outer circumference of the dust seal ring or the gap of the seal groove of the caliper will be troublesome. In addition, the dust seal in the sealing groove of the caliper may fall off due to deposition. Even if the dust-proof sealing ring falls off, the piston sealing ring in it will not leak immediately. However, if this situation is found, the caliper should be overhauled first.


The brake fluid and water combine to form a deposit.
Deposits may affect tightness.

Thoroughly remove deposits on the piston during overhaul

Although the dust seal did not pop out, the seal that deteriorated the brake fluid lost its elasticity. If the brake pads are worn and the piston protrudes too much, it may cause the piston itself to rust. Some older motorcycles have bellows dust seals, but Zephyr’s piston dust seals are square cross-sections of O-rings.

If you find the caliper piston and internal deposits in the caliper, remove them completely, and then replace them with new piston seals and dust seals. Even if something goes wrong, please do not perform a new seal with dirt remaining in the seal groove.

The brake oil inside the caliper is also wrapped inside the seal. Therefore, due to the dirt in the groove of the seal, it may cause new brake oil to leak and make the piston thrust uneven.

The dirt accumulated in the groove of the caliper is very hard, if you try to remove it by hand, it may damage the sealing groove. So let’s soak it in hot water as the first step. The brake fluid is hygroscopic, so it is easy to fall off when soaked in hot water.

The next time you clean, it is important not only to clean the visible parts with a precision screwdriver or cleaning tool, but also to clean the grooves and walls to make the piston seal and piston work properly. It is also effective to use special tools to clean the seal groove of the caliper.

▲This is the focus of caliper cleaning, the dirt has been soiled by sediment. Use special tools to scrape off the dirt accumulated in the sealing groove. Sometimes we use cleaning tools or precision screwdrivers, not only to clean the bottom of the seal groove, but also to remove the dirt on the wall, which is very important.

When cleaning the seal groove and installing a new seal, if a thin layer of rubber grease is applied to lubricate the metal and rubber, the seal will not be twisted when the piston is inserted, thereby reducing friction. It also has the function of protecting the surface of the caliper piston from moisture and corrosion. At the same time, regular cleaning of the calipers with neutral detergent and the use of rubber seal assembly sprays to lubricate and protect the surface can effectively avoid the generation of sediment.

▲The Zephyr caliper is a one-way type so it is easy to clean, but if it is an opposing piston caliper, the difficulty will be greatly increased. For the trouble of maintenance, the most effective method is to clean the caliper regularly and spray rubber sealant to wipe the piston, and apply a small amount of rubber grease on the piston oil seal and dust ring, so the grease is safer. Finally, please use the brake fluid with the coefficient specified in the maintenance manual correctly.


When replacing the sealing ring, thoroughly clean the inside of the caliper.
Regularly maintain and clean the calipers.

※Because the brake device is an important part related to safety, if you have insufficient experience, it is still recommended that you go to the car dealer to ask for help to be more safe.

Related news pages

[DIY Small Classroom]Tips for enhancing the brightness of old car headlights!

Presumably many old car inspections will encounter the experience of failing to pass the inspection due to insufficient headlight brightness. If the problem is not there… continue reading

[DIY small classroom]The key steps to adjust the tightness of the chain!

I believe everyone knows that according to the usual use situation and riding road conditions, as the mileage increases, the transmission chain will follow… continue reading

[DIY small classroom]Two-stroke engine that is easy to repair and fun

Normal maintenance is generally purposeful work, but many “holiday technicians” don’t know why, but I just… continue reading

[DIY Small Classroom]Discover the extraordinary features of H4 LED bulbs!

H4 headlight bulbs are usually used in large motorcycles, from the old age to the modern super sports car, there are many models that use… continue reading

Information provided by “Webike magazine”
“Webike Taiwan” editorial department compiled

Related Posts

Leave a Reply

Your email address will not be published. Required fields are marked *