I greased up the pivot part of the brake lever, but when I held the lever, something seems to be caught when the lever is gripped, and the movement is not smooth.
If you feel like that, you should look at the piston inside the master cylinder. Depending on how the lever and piston contact each other, extra force may be applied to the piston.
Pivot lubrication also extends the life of the parts
Greasing the brake lever is essential for delicate brake control. In that case, apply grease not only to the pivot bolt but also to the contact area with the master piston.
The principle of disc brakes is that the force of holding the brake lever is transferred to the piston inside the master cylinder, and the brake fluid pushed out of the piston pushes out the caliper piston, causing the pads to protrude and sandwich the brake disc. The master piston moves linearly in response to the input to the lever, enabling delicate brake control from light deceleration to full braking.
For that reason, it has been noted previously that the condition of the brake lever pivot, specifically regular cleaning and grease up is important.
However, in some cases, despite the grease up of the pivot part, the brake touch may not feel right at all. If you can separate it into with or without, it will work, but you may feel a slight tug when you start to squeeze the lever.
It is difficult to understand when gripping the lever, and when there is a feeling that something rubs when grasping lightly to control the speed, pay attention to the master piston itself.
- Greasing up the front brake lever is essential
- If you still feel friction, pay attention to the master piston
The diagonal force applied to the master piston is a problem
Piston took out from the master cylinder (the image is different from the work motorcycle). When the brake lever is squeezed, it moves to the left and pushes out the fluid in the brake master cylinder. As the lever slides over the end of the piston, a diagonal force is applied to the piston. At that time, if the frictional resistance is reduced by the grease applied to the end portion, the force will be enough to push the piston in a straight line.
The master piston is located inside the brake master cylinder and is an important part of pushing out the brake fluid. Therefore, the master piston is not possible to remove easily, and it does not come off easily because there is a snap ring of the omission.
Therefore, first observe the end of the master piston that can be seen by removing the lever. This is the part that the lever pushes when applying the brake, and there is a case where there is a mark in the contact part on the motorcycle with a lot of mileage.
Focusing on the movement of the brake lever, I draw a circle around the pivot bolt. Therefore, when the lever pushes the piston, the force to push diagonally is also generated separately from the force that pushes straight in. This diagonal push force causes one side of the top of the piston (or the front side if pushed diagonally forward by the lever) strongly against the inner wall of the master cylinder.
Certainly, brake manufacturers take measures to prevent this imbalance from occurring, but the mechanism of the lever pushing against the piston end is the same: the contact area between the lever and the piston end moves and pushes. Therefore, when cleaning and greasing the brake lever pivot, don't forget to grease-up the area where the lever and master piston make contact.
By the way, some supersport models and the radial master cylinders sold outside the factory are designed to make the contact area between lever and piston orthogonal to each other to eliminate friction and improve braking efficiency.
- Oblique force is applied to the piston by the lever movement path.
- The radial master can push the piston straight
Change the contact position with the lever by turning the piston
Grasp the end of the piston with a radio pliers, change the contact position with the lever by rotating the piston itself. If the lever and piston always contact at the same position and the end of the piston is dented, the piston tends to tilt accordingly, but it can be expected that the habit will be reduced if the contact position is changed. Be careful not to damage the rubber boots.
Back to the story, I wrote that I pay attention to the master piston when the operability of the lever is not good even if the grease up of the brake lever is not good, but I will rotate the master piston to change the position in contact with the lever and the brake master cylinder inner wall specifically.
Although it is not possible to say that this will improve the symptoms by 100%, the master piston with a contact mark with the lever at the end may be able to reduce the percentage of force pushed in an oblique direction by changing the contact position with the piston by rotating.
It is also effective to apply a lubricating spray to the gap between the piston and cylinder, which is effective in improving the slipperiness of the rubber and metal. The rubber cup seals assembled on the piston (which keep the brake fluid airtight) are wet by the fluid adhering to the seal, but by reducing the friction between the metal piston body and the master cylinder inner wall, the piston's movement when lightly grasped by the lever is smooth.
If the brake touch is uncomfortable, and there are clear contact marks on the piston end face or on the brake master cylinder itself (this can only be confirmed by disassembling the brake master cylinder), then replacing the brake master cylinder itself is the most reliable and appropriate course of action. However, if the wear and contact marks are minor, the symptoms may subside simply by turning the piston to promote lubrication.
When you remove the brake lever and grease up, check the state of the end of the master piston at the same time, and apply grease or turn the piston if necessary.
Turn the rubber boots slightly and apply lubrication spray between the piston and cylinder. It's important to use a lubricant that won't damage the rubber master cup, CCI's Metal Rubber Spray MR20, which is suitable for lubricating rubber and metal, or a silicone spray that is cup seal friendly.
- The contact position with the lever changes when the piston is turned
- Lubrication between cylinder and piston reduces friction.