The Importance is the Same for Both Mopeds and Larger Motorcycles | Scooter Disc Brake Maintenance You Want to do Before You Drag it Out

Brake maintenance cannot be neglected just because it is a moped. If your scooter is equipped with disc brakes, you will want to change the brake fluid and rub out the caliper pistons just as you would on a sports motorcycle or large motorcycle.
Check the remaining pads before they become iron brakes, as well as the cleaning and replacing of the parts to make them last longer.

Caliper pistons must be cleaned and greased to prevent sticking due to pad dust

An example of a front disc brake on a moped scooter. The caliper support (far right) is bolted to the outer tube of the front fork, and the caliper is attached to a pin on the support. The caliper slides along the pins and can pinch the brake rotor at the center of the caliper even if the brake pads wear out.

Piston seals and dust seals assembled to calipers are coated with rubber-compatible grease or brake fluid to reduce friction loss with the pistons. Since brake fluid is hygroscopic, it can cause rust if it adheres to the outside of the dust seal, so grease is safer.

Dust seals are available in square cross-section and bellows types similar to piston seals. The latter feature covers the sides to guard against dirt and rust even when the piston protrudes due to pad wear. However, it also has a weakness in that it is difficult to pull out if moisture gets between the bellows and the piston.

Disc brakes are equipped on 125cc class moped scooters not only at the front but also at the rear. Compared to drum brakes, disc brakes are attractive because of their high heat dissipation and controllability. However, unlike wired drum brakes, which require more lever play when the lining wears out, disc brakes are difficult to notice when the pads wear out because the lever touch does not change even if the pads wear out. Also, like sport motorcycles, brake rotors and calipers do not emphasize the sportiness of the brakes, and they tend to be hidden behind small-diameter wheels, making them difficult to notice.

The principle of hydraulic disc brake operation and care is the same for both large motorcycles and scooters, but for the aforementioned reasons, scooter disc brakes are often neglected, resulting in many instances of malfunctions and problems. The most common type of brake is the steel plate brake, in which the pads are worn out and the rotor is clamped by the back plate. Rotors with a worn-out surface need to be replaced, which is more expensive than replacing the pads. In addition, since the wheel diameter is smaller than that of a sports motorcycle and the brake itself is closer to the road surface, dirt such as rainwater and gravel can easily adhere to the rotor, which can also cause damage to the rotor.

To check the brake pad level on a scooter, you have to lower your viewpoint close to the ground, and since you are almost lying on the ground, you need to be prepared to do so. However, it is too late to check the pad level once it reaches zero, so if you hear a rubbing sound from the rotor and pads when pushing along, it is recommended to check the fluid level in the master cylinder or look into the calipers to check the pads.

Then, if the caliper is contaminated with brake dust from worn pads, the caliper body and piston should be cleaned and greased. For pin-slide calipers, which are common on scooters, it is important that the caliper moves smoothly over the sliding pins of the caliper support attached to the front fork. Therefore, when cleaning calipers, do not focus only on the pistons, but also check the condition of the caliper support slide pins.

If the caliper and caliper support are disassembled, the pins are checked for lubrication and rust, greased, and move smoothly, there is no problem. However, users who are usually careless in handling the caliper and often allow the wheel and caliper to come in contact with a parked curb, etc., may find that the slide pin is bent due to being pushed by the caliper. If the slide pin is bent too much, the rotor will be distorted, making it impossible to drive, which is easy to understand, but if the brake pad drags or wears unevenly while the motorcycle is ridable, the slide pin should be verified.

If there are no problems here, pull out the caliper pistons and overhaul them. If pad dust has accumulated on the piston, it should be polished with a metal polishing chemical, and if the caliper has had no maintenance for a long period of time, the piston seal and dust seal should also be replaced. A 4-pot opposed caliper on a sport motorcycle requires a total of 8 seals to be replaced, but a 1-pot caliper on a moped class scooter requires only 2 seals, so the cost is lower.

Master cylinders also need to be checked for diaphragm hardening and swelling

Disassembled master cylinder and replacement genuine parts (bottom). The primary and secondary cups are pre-assembled on the pistons of this model, but sometimes the cups are delivered separately even if ordered as a master cylinder piston. In such cases, the customer must perform the difficult task of inserting the cup with the smaller inner diameter into the piston with the larger outer diameter.

Originally, both calipers had the same shape, but the old one (left side) had swollen up due to being soaked in brake fluid for a long period of time. The pressure in the reserve tank could not be maintained at a constant level, and even if the calipers were overhauled, the brake feel would not improve.

If the calipers have been maintained, the master cylinder should be done as well. Scooter master cylinders often have smaller reservoir capacities than those of sports models, and if the fluid is not changed regularly, it often becomes dirty and brownish. Depending on the model, it may be time-consuming to remove the master cylinder, which is covered by a cover around the meter, but an overhaul will certainly restore lever touch and performance.

The most important parts of the master cylinder are the primary and secondary cups attached to the piston and the diaphragm behind the reservoir cap. The cross sections of the two cups are open like an umbrella, and they push the fluid inside the master cylinder through the brake hose to the calipers. If the fluid inside the master cylinder becomes deteriorated after a period of inactivity and gets trapped in the cups, the sealing property will deteriorate, causing fluid leakage, and the pistons will not move smoothly, so they must be replaced.

The primary and secondary cups of OEM parts are generally set up as a set with the pistons, but there are cases where the seals are built into the pistons at the time of purchase, or where the pistons and seals are delivered separately. In the former case, the piston in its assembled state can be simply assembled into the master cylinder, but in the latter case, it is very difficult.

As you can see in the piston in the image, the outer diameter of the piston and the outer diameter of the cup is almost the same, and the diameter of the cup assembly area is narrowed to about half. This means that the inner diameter of the cup has to be widened when it is assembled. It is very difficult to set the cup on the piston while expanding it, because the outer diameter of the cup, as well as the inner diameter, must not be damaged.

There are special tools for cup assembly for automotive pistons that are shaped like a rocket, but there are no tools for motorcycle pistons, which have a narrower diameter, so care must be taken. However, there are no tools for motorcycle pistons, which have a narrower diameter, so care must be taken.

Compared to the piston cup, which applies pressure to the fluid and pushes it out, the diaphragm, which is often thought of as a mere lid, is another important component. The diaphragm is installed to seal the opening of the reserve tank, and when the brake lever is held and the fluid in the tank decreases, the bellows part extends to follow the decrease and returns to its original shape when the lever is released and the fluid returns to the tank.

If the diaphragm loses flexibility due to aging or other factors, the diaphragm will not stretch when the fluid in the tank decreases, and the pressure in the tank will decrease. In other words, the diaphragm is responsible for maintaining a constant pressure in the reserve tank. Therefore, if the diaphragm becomes less flexible or deformed and does not return to its original shape, it must be replaced.

As mentioned in the introduction, the basic structure of hydraulic disc brakes is the same for both moped scooters and big motorcycles, which is why maintenance should be done in the same way. Although scooters are often used more as a practical practical means of transportation than as a hobby motorcycle, and are often left to be ridden, do not neglect maintenance.