Normally forbidden! A sticking brake caliper piston that won't budge is pushed out with water.

The brake fluid that operates the disc brakes is hygroscopic, and moisture in the air can lower its boiling point and cause problems such as vapor lock. Therefore, it is necessary to replace it periodically. When pulling out the pistons during brake caliper maintenance, it is common to use air from a compressor, but sometimes the dust seals or piston seals become altered and the pistons do not move at all no matter how much air is applied. In such cases, water, which is supposed to be the enemy, can be relied on.

Caliper piston sticking, which is common in cars that have been immobile for a long time

You may not be aware of this when you normally ride your bike, but the piston seals and dust seals built into brake calipers stick to the caliper pistons to prevent brake fluid leakage, and as the brake pads wear, they gradually They are special and important parts that position the caliper pistons, which gradually move outward as the brake pads wear. The caliper piston, which is pushed out of the caliper and clamps the disc rotor with the brake pads when the brake lever is squeezed, and pulled back into the caliper when the lever is released, gets dirty from worn pad dust and dust and gravel that adhere to it while driving, so it needs to be cleaned regularly. Caliper piston rubbing is a basic maintenance procedure, but skipping it can cause various problems and troubles such as brake pad drag, uneven wear, and caliper piston corrosion. The ultimate of these problems is caliper piston sticking. Piston sticking never occurs on a bike that is regularly ridden, but there is nothing that can be done if, when pushing a bike that has been left unattended for a long period of time, the brake lever is squeezed unnecessarily and the tire locks up because the brake is still applied.

I don't want to spray brake fluid all over the place, so I want to air it out, but ......

If you somehow manage to remove the caliper from the body and remove the brake pads, just grab the brake lever for now. If the piston moves even slightly, there is a possibility of revival. However, if you pump the brake lever as it is, you will release the piston and spray brake fluid around it at the same time. In order to prevent brake fluid from splashing around and damaging the paint, it is common practice to disconnect the brake hose from the caliper and feed air from a compressor into the caliper. What is worse, the dust seals and piston seals can change or swell. It is true that the caliper pistons need to be cleaned, but depending on the chemistry used, the rubber material of the seals may be adversely affected. Therefore, it is considered safe to use a neutral detergent solution when rubbing out caliper pistons. Since rubber seals that have become altered and sticky are stubborn, it is more reliable to push them out with a liquid than with an air blow. Then, it is quicker to connect the brake hose once disconnected and inject brake fluid, but as mentioned earlier, we do not want to work with the possibility of inadvertently getting brake fluid on the painted surface. In such cases, we can rely on water, the natural enemy of brake fluid.

With water, there's no need to worry about the calipers popping off and into the surrounding area.

Needless to say again, brake fluid and water are like water and oil. If brake fluid, which gets hot when the brakes are applied, boils and creates air bubbles inside the calipers and brake hoses, squeezing the levers will only compress the air bubbles and the brakes will not work. To avoid this condition, known as vapor lock, the boiling point of brake fluid is set at 200°C or higher, but even a few percent of moisture in the fluid can cause a dramatic drop in temperature. Brake fluid is also highly hygroscopic, so it absorbs moisture from the air, which also causes the boiling point to drop, and is therefore specified to be replaced periodically. Therefore, under normal circumstances, there is absolutely no way to mix brake fluid and water, but if the job is to push out sticking caliper pistons, it is a different story. Whether it is brake fluid or tap water, the fluid pushed out of the master cylinder is transmitted to the caliper without compression, and the caliper pistons are pushed with the same powerful pressure that is applied when the brakes are applied, and can be pulled out securely. It is no exaggeration to say that if the sticking is so severe that even water cannot push it out, it cannot be pulled out by any other means. For example, if the piston is rusted and fat and stuck inside the caliper, there may not be much point in forcing it out, since the caliper's inner wall is likely to be damaged and cannot be reused. Otherwise, i.e., if the piston sticking is caused by a foreign object with altered rubber seals or brake fluid that has hardened into a tickle, water in place of fluid should be able to pull it out. The greatest advantage of using water is that there is no adverse effect on the surroundings. Whether it is popping out of the master cylinder reservoir tank port like a fountain when the lever is squeezed, or dripping from the bleeder plug to bleed air from the calipers, there is no need to worry about anything with water. Of course, water that flows out of the caliper when the piston is pushed out will not damage the paint.

Thorough water removal is essential when replacing water to fluid.

The work here was done by switching to the use of water in the middle of the process because the air gun did not work well to push it out, but the power of the water pressure was overwhelming. The water pressure was overwhelmingly powerful. Even the sticky and deteriorated dust seals were not a problem, and the pistons were pushed out forcefully and safely removed. The brake fluid that had turned to jelly inside the caliper was also removed by soaking it in hot water, and the caliper and piston could be reused if new piston seals and dust seals were replaced. However, thorough drying is essential when reusing the brake lines after they have been soaked with water. As explained earlier, even the slightest amount of moisture will lower the boiling point of brake fluid. Brake calipers that require seal replacement must be washed with water, but the master cylinder, brake hoses, and banjo bolts should also be dried by blowing water out with an air blower. If the car has been neglected for a long time, this is a good time to disassemble the master cylinder as well and replace the piston and cup seals. Furthermore, if there is a master cylinder among the junk parts that is not being used due to a wrong piston diameter or some other reason, you can use it as a "pop! It can also be used as a caliper piston tool that can be pushed out more gently than an air blow gun, which may pop out the caliper piston. Normally, maintenance should be performed before caliper pistons become stuck, but in the unlikely event that they stick and there is nothing you can do about it, remember that there is a way to pressurize them using water instead of brake fluid. .

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