Watch Out for Disc Brake Pad Springs! Removing it Unconsciously May Cause Problems During Assembly

Although the configuration differs depending on the model, a thin metal part called a pad spring or retainer is incorporated between the caliper and pads of a disc brake. They come off easily when replacing the pads, and it is sometimes difficult to find the direction of assembly once they come off, but they are very important parts, so it is important to check the front and back and the direction of assembly before disassembling.

It suppresses pad play and reduces brake squeal.

Front brake caliper for Kawasaki GPZ400F with single push piston. The pads in contact with the caliper piston are held by the caliper support, and the pads on the backside of the rotor are held by pins, so no retainer is used. The T-shaped plate at the back of the caliper piston is pad spring.

In a disc brake, the caliper piston pushes the pads, which pinch the rotor to provide braking force. The pads open when the brake lever is released, thanks to the elastic deformation of the rubber piston seal between the caliper and the piston, but there is another important part of the brake caliper. That's what pad springs and retainers are for.

Some models do not use retainers depending on the shape of the caliper and how the brake pads are held in place, but pad springs are always incorporated. Both are intricately bent and formed from thin metal plates, and are incorporated between the caliper and the pads. The retainer guides the pads so that they move smoothly during braking. The pad spring is responsible for keeping a constant pressure on the pad.

The brake pads are pushed out by the caliper piston and pulled into the caliper by the elasticity of the piston seal, and the brake pads move in the orthogonal direction (thrust direction) to the rotor. In order for the pads to move smoothly, there needs to be a certain amount of clearance between each part, but a gap can also cause vibration. Therefore, the pad springs are used to add tension to the pads to prevent them from moving on their own.

Pad springs are designed to
1. Reduce brake squeal caused by vibration of the pad itself
2. Reduce wear of brake caliper and pad.
3. Preventing the pad pins from loosening or falling off

The pad spring, which is fitted at the back of the caliper body and restricts pad movement by pressing down on the end face of the brake pad, can contribute to friction loss if you only consider pad operation. Therefore, there are some race users who remove the springs because they don't want the pads to drag, but there is also a growing movement to regulate the removal of the springs because of the accidents that have occurred when the pins have fallen out due to the loss of force to hold the pad pins. Even though it prevents the pads from moving, the friction can be reduced to a negligible level through maintenance and the benefits are far greater, so the spring should always be installed.

Sometimes the spring falls off as soon as the pad is removed.

When the brake pads and caliper support are removed, the pad springs are housed behind the caliper. This is the most common arrangement for single push type calipers. If a retainer is attached, it is set on the caliper support side.

In the case of opposed piston calipers, the brake pads are generally held in place by pad pins, and the pad springs provide tension to the pad pins as well as holding down the brake pads. Since that tension prevents the pins from loosening or coming loose, the pad springs should not be removed for the purpose of reducing friction loss.

The pad spring lightly pushes the brake pad from the outside (outer side of the rotor) to the inside. Therefore, on some models, when the pads are removed from the caliper, the pad springs are also removed at the same time. especially in the case of opposed piston calipers, the spring is pushing the pad pin, so pin removal = spring removal.

One thing to keep in mind here is the orientation of the pad springs. However, in the case of a single piston, if the spring is placed in the back of the caliper in the wrong direction, the spring may be damaged, the pad may not be tensioned properly, or the spring may interfere with the rotor, causing abnormal noise. The spring and rotor may interfere with each other and cause abnormal noise.

A further danger is that the pads may not work properly due to incorrect spring assembly. It is normal for the pads and springs to come in contact with each other, but if they are assembled in the wrong direction, they will come in contact with each other in a different place than they should, and the pads may get stuck on the springs and not work properly. Since the disc brake fluid pressure is stronger than the pad spring strength, when the brake is applied, the pad will clamp the rotor even though the spring is deformed. However, when the lever is released, the pads may get stuck and not return smoothly, or the deformed spring may hit the pads partially, causing uneven wear.

To prevent such misassembly, check the position and direction of the pad spring assembly before removing the brake pads. If you leave a lot of pictures before disassembly, it will be helpful for assembly. Although illustrations of the brake caliper components may be provided in the service manual or parts list, it is recommended that you take images of the components from various angles, as the illustrations may not be subtle enough to understand. When removing the retainer built into the caliper, be sure to keep the images so you don't forget the position and orientation.

The direction of assembly is also hinted by the rubbing marks on the pads.

The two rows of peaks in the center of the pad spring lightly press the back plate of the brake pad to prevent the pad from playing and squealing. You can see slight metallic luster on the red rusted part, this luster is the trace of contact with pad. If you find rubbing marks on wrong place, it means spring is assembled wrongly.

In the case of this brake caliper, if the positional relationship between the pad spring and the pad is correct, the spring claw will hang on the outer pad. The material of the spring is soft, so it can be assembled even if it is assembled incorrectly, but be careful because the pad may get caught in the middle or the contact with the rotor may become uneven, causing the brake to drag.

The pad spring assembled to the caliper should be dirty with brake pad dust, etc. If the pad spring is removed for brake pad replacement or caliper cleaning, clean it with a mild detergent or brake cleaner. If the spring fixed on the single push piston caliper does not come off easily, there is no need to remove it forcibly and clean it with detergent together with the caliper.

When restoring, as explained earlier, it is important to set the top and bottom and the reverse side correctly. If you assemble it according to the picture I took before disassembling, there should be no problem. If the spring is hitting the pad correctly and applying tension, it will leave a rub mark in contact with the pad. It should be, so that's another important clue. If you set the spring in the caliper and temporarily assemble the pads, and the rub marks left on the outside of the pad and the spring are clearly hitting in different positions, then the spring is probably assembled incorrectly and should be corrected.

Some users also apply brake grease to the contact area with the spring and retainer, and to the pad pins to reduce friction.

It is more important than anything else to take a picture of the assembled state before disassembly, because you will be in a hurry if the pad spring drops as soon as you remove the pad.