Motorcycle Brake Caliper Maintenance Guide

Author: William Davis
Experience: Five years as a motorcycle mechanic

Basic Knowledge Of Brake Calipers

Working principle

Simply put, when you pinch the brake lever or step on the brake pedal, you are actually “giving orders” through a hydraulic system “.

First, the force you apply will act on the piston of the brake master cylinder. This piston will push the brake fluid (1 an incompressible liquid) in the master cylinder to the brake hose. Imagine, just like you push water with a syringe, the pressure is transmitted instantly.

The pressurized brake fluid runs along the tubing and eventually reaches our protagonist, the brake calipers. Inside the caliper, the brake fluid pushes the piston in the caliper. Note that the piston here is not one, the number depends on your caliper type.

When the pistons are pushed, they act directly on the brake pads. The brake pads tightly clamp the high-speed rotating brake disc under the pressure of the piston. Friction occurs, and then your motorcycle starts to slow down until it stops. The whole process may seem complicated, but it is actually as fast as lightning. This is the charm of hydraulics.

Main Types and Structures

In the world of calipers, there are two main camps: fixed calipers and floating calipers.

• Fixed caliper: This caliper is fixed on the shock absorber and will not move left and right. It has pistons on both sides. When braking, the pistons on both sides push the brake pads inward at the same time to clamp the brake disc. Fixed calipers usually have more pistons, stronger braking force, and better heat dissipation. They are the first choice for high-performance motorcycles and racing cars. Disadvantages, the cost is relatively high, and maintenance may require more skills.
• Floating caliper: As the name suggests, this caliper can “float” and is mounted on the bracket through a sliding pin. Usually there is a piston on only one side. When the piston pushes the inner brake pad to contact the brake disc, the caliper itself will move outward along the sliding pin, thereby driving the outer brake pad to also clamp the brake disc. Floating calipers are relatively simple in structure, low in cost, and lighter in weight. They are common in ordinary commuter motorcycles. Although the braking force is not as strong as the fixed type, it is completely sufficient for daily use.

As for the number of pistons, there are single pistons, double pistons, four pistons and even six pistons. The more pistons, usually means that the brake pads are more evenly stressed, the braking force is stronger, and the feel is more linear. But I think quantity is not the only criterion, design and matching are equally important.

Photo: Motorcycle Caliper Breakdown Structure Diagram

Key components

A caliper may seem simple, but every small part inside it plays a key role.

• Piston: As mentioned just now, it converts hydraulic pressure into mechanical force to push the brake pads. The piston material is usually aluminum alloy or steel, and some high-performance ceramic pistons are also used for better heat insulation.
• Piston Seal: This is a very critical but easily overlooked component. It surrounds the piston and has two main functions: the 1 is to prevent brake fluid leakage, and the 2 is to return the piston. When the brake fluid pressure is released, the elastic deformation of the sealing ring will cause the piston to return slightly, leaving a gap between the brake pad and the brake disc to avoid dragging the brake. If the sealing ring is aging, the problems of oil leakage and poor return will come, which will seriously affect the braking performance and safety.
• Dust Boot: sleeved outside the piston, mainly to prevent dust, moisture and other foreign matter from entering the caliper and corroding the piston and sealing ring. Don’t underestimate this layer of rubber, its health is directly related to the life of the caliper.
• Bleed Nipple/Screw: Usually at the highest point of the caliper. It is used when changing brake fluid or removing air from the brake system. Every time I change the brake oil for the riders, I will emphasize the importance of emptying the air, because the air is compressible. Once there is air, the brake feel will become “soft” and even the car will not stop.
• Pad Pin/Bolt is used to fix the position of the brake pads in the caliper so that they will not run around. Some calipers also use spring plates to assist in fixing.
• Caliper Body Material: Most of the caliper body is cast in aluminum alloy because it is light and strong enough. Some high-end calipers will use forging technology, or even one-piece forging (Monobloc), to further improve rigidity, reduce deformation during braking, and provide a more linear feel. One-piece calipers, in my opinion, are simply works of art.

Common Fault Diagnosis And Troubleshooting

In my maintenance career, I have encountered all kinds of strange caliper problems, but they are always the same. As long as I master the diagnostic methods, most of them can be solved.

Brake caliper rattle

This is the most common problem for car owners.

• Cause analysis:
  • Brake pad wear: The most common. When the brake pads are used for a long time, the friction material becomes thinner, and the metal indicator inside will start to rub against the brake disc, making a harsh “squeak” sound.
  • Foreign matter: Small stones, sand or other debris stuck between the brake pads and the brake disc will also produce a rubbing or rubbing sound.
  • Caliper piston jam: If the piston cannot return smoothly, the brake pads will always touch the brake disc slightly, making a continuous rubbing sound.
  • Improper installation: For example, the brake pads are installed backwards, or the caliper screws are not tightened, which will cause abnormal noise.
• Diagnostic steps:
  • Listen to the sound: listen carefully, is it continuous, or does it only appear when braking? Is it a sharp metal friction or a low rubbing sound? This can initially determine the direction of the problem.
  • Observe wear: check the wear of the brake pads by removing the wheels. If the wear is to the limit, then 80% is it. At the same time, see if there are any abnormal scratches on the brake discs.
• solutions:
  • Cleaning: The problem can sometimes be solved by cleaning the foreign matter around the caliper and spraying it with brake cleaner.
  • Replace the brake pads: If the brake pads are severely worn, don’t hesitate to replace them directly.
  • Piston maintenance: I clean and lubricate the piston if I suspect it is stuck, and replace the sealing ring if necessary.

Brake feel abnormal

brake feel the causes of abnormal:

• Brake oil “changed flavor” or “drank water”: many car owners and friends may not know that brake oil is different from vegetable oil we eat. It especially “loves” to absorb water. The water vapor in the air is pervasive, and the moisture content in the brake fluid is high 1 a long time. A lot of water, the boiling point of the brake oil down. If you think about it, when you 1 the foot brake, the temperature of the caliper piston is frighteningly high, and the water-containing brake oil is easy to boil, and bubbles are produced when the 1 boils. These bubbles 1 form. When you pinch the brake, it is like pinching cotton. It is soft and the stroke becomes longer. That is called a lack of confidence! My personal experience is that most of the brake fluid deterioration, with this “drinking water” can not be switched off.
• The brake system “air in”: one of the most common problems when we repair cars. Air, unlike liquid, can be compressed. Your brake system is originally a closed hydraulic circuit. Once air runs in, when you pinch the brake, part of the braking force is used to compress the air instead of actually pushing the piston. As a result, the brake feels weak and the stroke becomes long. You have to pinch it to the end to barely stop. That feeling is really frightening.
• The piston is “lazy” and stuck: the piston in the brake caliper of a motorcycle, like the piston in an engine, needs to be pushed out and returned smoothly. However, if it is not maintained for a long time, or if there is sand or rust intrusion, the piston may be stuck. If the piston is stuck, it may cause the brake pads to fail to fully return to position, causing the brake to drag. Over time, the brakes will lock up, or vice versa, the piston is not pushed in place, the braking force is insufficient, and 1 the brake is like tickling. In my personal judgment, piston jams are often gradual, and you may not feel them 1 at first until they become more and more serious.
• Caliper “not well”: although this kind of situation is rare, it must be guarded against. Sometimes, the caliper installation position is slightly deviated, or the screw is not tightened, which will affect the contact uniformity between the brake pad and the brake disc. Uneven contact, the braking force will naturally be uneven, and the hand will naturally become strange. I usually double-check the installation details to make sure it’s foolproof.

How to diagnose the fault?

• Step 1: Check the brake oil “face”: I will unscrew the brake oil pot lid and carefully observe the color of the brake oil. Normal brake fluid should be clear and transparent, a little light yellow. If I see that the color of the oil has become dark, brown or even black, then I don’t need to think much about it. The brake oil must have “deteriorated” and must be replaced quickly. If you see obvious sediment at the bottom of the oil can, you can’t be careless.
• Step 2: Try the “exhaust” solution: I usually start with the exhaust if the brakes feel soft and inflexible. Use a professional tool to connect the exhaust screw and slowly exhaust the air in the brake system. During the exhaust process, I will carefully observe whether there are bubbles in the discharged brake fluid. If a large number of bubbles are discharged, it means that the problem is probably here. This is a delicate job that requires patience and experience.
• Step 3: Piston “physical examination”: If the hand still feels bad after exhausting, or there is a lock or drag brake, then I have to remove the caliper and check the piston. I will use special tools to gently push the piston to observe whether the process of pushing and returning it is smooth, and whether there is any sense of Caton or blocking. At the same time, it will also look at the surface of the piston for rust, scratches or sludge.

How to troubleshoot?

• Brake oil “big change”: as I often say, it is necessary to change brake oil regularly! This is not a decoration. In general, I suggest that every two years, or every 20000 kilometers, you have to give your car a brake oil “big change”. This is as important as changing the engine oil regularly. It can effectively prevent the brake fluid from deteriorating and absorbing water and ensure the normal operation of the brake system.
• “Emptying” the air: Emptying the air is indeed a technical job, not just finding a screw to screw 1 to screw it. It requires professional exhaust tools, such as vacuum pumps, or professional pressure exhaust equipment. More importantly, it requires experienced technicians to operate to ensure that every trace of air in the system is completely discharged without leaving dead corners.
• Piston “maintenance”: For the problem of piston sticking, we usually remove the caliper and thoroughly clean the sludge and dirt on the surface of the piston and the inside of the caliper. If the sealing ring is found to be aging or damaged, it must be replaced with a new sealing ring. After cleaning and replacing the seal ring, apply special brake piston grease to ensure that the piston moves freely. I always tell the owner, don’t underestimate these small seals, they are the key to the normal operation of the piston!

Oil leakage

Oil leakage means that the brake system has a potential risk of failure.

• Cause analysis:
  • Sealing ring aging and damage: The oil seal and piston sealing ring inside the caliper will age and harden after a long time, resulting in poor sealing.
  • Bleed screw loose: only a small screw is sometimes not tightened, can also cause oil leakage.
• Diagnostic steps:
  • Visual inspection: Observe carefully around the caliper for oil stains. Especially the connection between the piston and the bleed screw.
  • Pressure Test: A pressure test is performed to confirm if a problem with the internal seal ring is suspected.
• solutions:
  • Replace the seal ring: the most common solution. Replace with new original seal ring.
  • Fastening screw: Tighten it if only the bleed screw is loose, but check whether the sealing gasket is intact.

Caliper piston stuck

Piston jams will directly affect the braking effect and even cause excessive wear of the brake disc.

• Cause analysis:
  • Dust, rust: exposed to the external environment for a long time, dust, sand and moisture can easily lead to rust or scale on the surface of the piston.
  • Lack of lubrication: Lack of proper lubrication between the piston and the sealing ring will also increase the possibility of seizure.
• Diagnosis and repair:
  • Safe disassembly: Be careful not to injure other parts when removing the caliper. Use the brake oil to pump the piston first, but do not take it out completely.
  • Cleaning: Thoroughly remove the dirt and rust inside the piston and caliper using professional piston cleaning tools and brake cleaner.
  • Lubricate and reset: After cleaning, apply special piston lubricant, and then carefully reset the piston. I usually use a piston reset tool to ensure that it is pushed in evenly.

Routine Maintenance And Maintenance

The caliper is like the “hand” of a motorcycle. It firmly grasps the brake disc and lets our car stop when it stops. But no matter how good the hand is, it will be rusty and stiff without maintenance. Therefore, daily maintenance is particularly important.

The importance of cleaning: when to clean, how to clean the outside of the caliper and the exposed part of the piston.

Clean, seemingly simple, but many doorways. I recommend that you perform a simple external cleaning of the calipers at least every 3000 kilometers or every time you wash the car. Especially for those friends who like cross-country and mountain running, sand and dust are more likely to adhere. When cleaning, I will use professional brake cleaner, spray on the outside of the caliper, and then gently scrub with a soft brush to rinse off.

For the exposed part of the piston, I will carefully wipe it with a clean soft cloth to make sure there is no residue. Remember, cleaning is not to look good, but to prevent foreign matter from entering the caliper, affecting the smooth movement of the piston.

Check the brake fluid: regularly check the oil color, level, and when it needs to be replaced.

Brake fluid is the “blood” of the caliper, which conveys the instructions of our fingers to the brake lever. It is essential to regularly check the color and level of the brake fluid. Normal brake oil should be clear and transparent or slightly yellowish.

If the oil is found to be dark, turbid, or even black precipitation, it means it should be replaced. I usually recommend replacing the brake fluid every 1-2 years, even if the liquid level looks normal, because the brake fluid will absorb moisture in the air, causing the boiling point to decrease and affecting the braking performance. Low liquid level may be a sign of excessive brake pad wear or leakage in the system, which should be highly valued.

Check the brake pad wear: how to determine whether it needs to be replaced, and choose the appropriate brake pads.

Brake pads are consumables, and their wear directly affects the braking effect. I will regularly check the thickness of the brake pads. Usually the thickness of the new brake pads is about 4-5mm. If it is worn to only 1-2mm, it must be replaced immediately. Some brake pads will have wear indication grooves to facilitate our judgment.

In addition, if you hear the harsh sound of metal friction when braking, it is mostly because the brake pads have been worn to the limit and the friction has reached the brake disc. This is not a small problem. When choosing brake pads, I will recommend the original factory or a reliable subsidiary brand according to my riding habits and budget. Don’t be greedy for petty gain, inferior brake pads are not only not durable, but also life-threatening.

Piston dust cover inspection: make sure they are intact to prevent dust and moisture from entering.

The piston dust cover is like the “protective umbrella” of the caliper, which can effectively prevent dust, moisture and foreign matter from entering the gap between the piston and the caliper body, thereby protecting the piston and oil seal. When I check, I will pay special attention to whether the dust cover is cracked, aged or damaged.

If any problems are found, even a little crack, I will recommend the owner to replace it as soon as possible. Don’t underestimate this thin layer of rubber ring. Once it fails, the piston will be exposed to harsh environments, accelerate wear, and even cause brake fluid leakage, which can be in big trouble.

Screw torque: emphasis on tightening according to manufacturer’s specifications, avoid over-tightening or over-loosening.

Screw torque, which is often overlooked but extremely critical details. The fixing screws, bleed screws, etc. of the calipers shall be tightened according to the torque specified by the manufacturer. Too tight will cause the screw to slip, the caliper to deform or even break; too loose may cause the caliper to loosen, affect the braking effect, and even fall off in extreme cases, with disastrous consequences.

I usually use a torque wrench to make sure that each screw is tightened just right. I don’t recommend that you twist the screws with your hands. This is no joke.

Replacement And Upgrade Of Brake Caliper

I often run into friends who ask me, “Master, my brakes don’t feel right, should I change the calipers?” Usually I ask them to describe the specific situation first, because the calipers are usually repairable unless they are really broken. But there are always times when it really dies, or when you pursue higher performance, then replacement and upgrade are on the agenda.

Replacement time: the caliper is seriously damaged, cannot be repaired, and the performance drops obviously.

First of all, the most intuitive is that the caliper body has visible cracks, deformation or severe corrosion. In this case, I will definitely recommend you to replace it directly. There is no repair value and the safety hazard is too great.

Secondly, the piston is stuck and the oil seal leaks seriously, causing the brakes to feel soft and weak, or the brake pads are abnormally worn. If the problem still occurs repeatedly after repeated cleaning and replacement of the oil seal and piston (the so-called “caliper renovation”), or the casting inside the caliper has been severely worn and cannot ensure the smooth movement of the piston, then my experience tells me, It’s time to consider a new one.

Some old calipers, even if all the seals are replaced, the oxidation and unevenness inside the piston cavity may cause the new oil seal to fail quickly. At this time, the cost and time of repair may be higher than that of a new one, which is not cost-effective.

Finally, you obviously feel the brake performance degradation, such as the braking distance becomes longer, and the lack of braking force in an emergency. This may not only be a problem with brake fluid or brake pads, but the wear inside the caliper may also be behind it. Of course, specific problems have to be analyzed in detail, but if you rule out all other possibilities, the caliper is the weak link, then don’t hesitate.

Removal and installation steps:

Disassembling and installing the calipers, in my opinion, although it is not particularly complicated, it definitely requires care and patience. I usually do this:

1. Preparation: first frame up, to ensure stability. Prepare the necessary tools, such as sockets, wrenches, piston reset tools, torque wrenches, as well as new brake fluid, clean rags and waste oil basins. I usually also prepare 1 bottles of brake cleaner to keep the work area clean.
2. Loosen the bolts: first loosen the caliper fixing bolts with a suitable sleeve, usually two. Note that it is only loosened, not yet fully unscrewed.
3. Removing the old caliper: After the bolts are loosened, carefully remove the old caliper from the brake disc. I am used to using the piston reset tool to push the piston to the end first, so that it is easier to remove the caliper. Then, disconnect the brake hose. Remember, when you disconnect the oil pipe, you must use a waste oil basin below. The brake oil is corrosive.
4. Cleaning and Inspection: Before installing the new calipers, I carefully check the brake discs for uneven wear or deformation. If there is a problem with the brake disc, it should also be replaced. Clean the hub and mounting base to ensure that there is no oil and impurities.
5. Install the new caliper: Install the new caliper on the mounting base, and first screw the fixing bolts by hand. Connect the brake hose and tighten the bolts with a torque wrench according to the torque specified by the manufacturer. This step is very critical, insufficient torque may cause the bolt to loosen, and excessive tightening may damage the thread or caliper body.
6. Install brake pads: Install new brake pads into the caliper. Make sure the brake pads are in place and move freely.

Choose the right replacement caliper: original vs auxiliary factory, performance upgrade option

Choose calipers, this knowledge can be big.

• Original calipers: the safest choice, directly buy the original calipers of the corresponding models, generally can be perfectly matched, the quality is guaranteed. But the disadvantage is that the price is usually higher.
• Brand auxiliary factory calipers: There are many well-known brands of auxiliary factory calipers on the market, such as Brembo, Nissin, Tokico, etc. These brands of calipers are often not inferior to the original factory in terms of performance and quality, and may even be better, and there are more price options. However, we must pay attention to distinguish the authenticity when buying. There are too many fake and shoddy products now.

If you want a performance upgrade, that multi-piston caliper is a good choice.

Multi-piston calipers (such as four-piston, six-piston calipers) can provide stronger braking force and more uniform brake pad wear. The more the number of pistons, the better the braking effect and the better the heat dissipation.

I usually recommend according to the model, riding habits and budget of the motorcycle friends. For example, if you only commute instead of walking, original calipers or good quality double piston auxiliary factory calipers are enough. However, if you are a track enthusiast and pursue extreme braking performance, upgrading a set of radial four-piston or even six-piston calipers with large-size floating discs will definitely feel different.