Check the Slide Pin of the Brake Caliper if it’s Heavy When Pushing Around Before Customizing!

From mopeds to big motorcycles, no matter how big or small the displacement or how light or heavy the weight of the motorcycle is, if the motorcycle is in good condition it will feel light, and if something is wrong with it, it will feel heavy somehow. An often overlooked cause of brake-related "heaviness" is insufficient lubrication of the slide pin of the single push caliper. If the tire does not rotate lightly, check the movement of the caliper.

The difference between braking and not braking is just a small amount of slide

The front brakes on Suzuki's underboned sports models that were produced in Indonesia are fitted with a single push 2-piston caliper. This caliper is apparently used in the small to 250cc class in Japan. The slide pin seems to have corroded during three years of storage in the warehouse, and once I squeezed the lever, the brake locked up. I have no idea why only the slide pin got rusted because the other parts are not rusted at all.

In a disc brake caliper, the caliper pistons are on both sides of the brake rotoropposed-piston caliperand the piston is on one side of the rotor.single-piston caliperThere are. Needless to say, the brake pads are on both sides of the rotor, both opposing and single push, but the way the pads are moved is different, or rather the caliper itself is different.

In opposed piston calipers, the pads on both sides of the rotor are pushed out by the caliper pistons and sandwich the rotor. The caliper body is therefore fixed to the front fork. In contrast, in a single-piston caliper, when the pad on the side with the piston comes into contact with the rotor, the reaction force causes the caliper to slide parallel to the axle shaft, pulling the pad on the opposite side and sandwiching the rotor. To do this, the caliper support has a sliding pin and the caliper has a guide that receives the pin.

As far as which is better, opposed-piston calipers are the winner due to the fact that many racers and supersport models use them. In particular, the radial mounting system, where the caliper mounting bolts are perpendicular to the axle shaft, which is the hallmark of modern high-performance brakes, does not allow the caliper to slide in the direction of the axle shaft. This does not mean that single-piston calipers are inferior, and they are still used in a wide range of models from small to big motorcycles. Because the piston is only on one side of the caliper, the backside of the rotor (the wheel side) is less protruding, making it easier to avoid interference with the spokes.

The reaction force of the pads being pushed by the piston on one side causes the caliper itself to slide and push the pads on the other side against the rotor. When written like this, it may seem that the motion is two-step and not very responsive, but when you actually operate the brake lever or pedal, this motion takes place almost simultaneously. Strictly speaking, it's two motions, but how many riders can separate the motions and feel that "I just hit one side of the rotor" and then "I hit the other side"?

In fact, two steps of motion can be recognized as one action because the caliper slides only a fraction of the distance. If it were a large movement, such as the pad on the piston side moving 5mm until it hits the rotor, and then moving another 5mm until the pad on the other side hits the rotor, it would obviously be recognized as two motions, but in reality the gap between the pad and rotor is very small. The basic operating principle of hydraulic disc brakes is that when you hold the brake lever, the piston moves forward to push the pad and pinch the rotor, and when you release the lever, the piston moves back by the amount of deformation of the caliper piston seal.

By releasing the lever, the piston moves back into the caliper slightly, and at the same time, the force applied to the caliper itself is released, causing the pad opposite the piston to slide slightly along the pin and away from the rotor.

One-piston calipers may look and perform more modestly than opposed-piston calipers, but the mechanism is surprisingly complex and delicate and requires proper maintenance.

The sliding pin of a single push caliper is the key to braking

Pushing the caliper too hard could bend the thin solid rotor, so I managed to remove it by pushing only minimally, just enough to get the tire to turn, and then removing the caliper support bolt and pushing the caliper itself out to the outer edge of the rotor. The pin was firmly attached and there was no sign of the support coming loose.

If you pry the gap between the caliper and caliper support with a flat head screwdriver or tire lever, there is a risk of twisting the pin remaining in the caliper and the support itself. It is important to pull the pin out without bending it, because if it twists here, the contact between the caliper and the rotor will change. The caliper piston tool as shown in the image is difficult to pry because the jaws on the tip open in parallel.

When it comes to disc brake maintenance, replacing pads and rubbing out pistons are well known, but just as important as these is lubricating the slide pins. As explained earlier, single-piston calipers must slide according to braking. The opening of the guide hole in the caliper body where the pin on the caliper support side pierces is fitted with a rubber boot that keeps the pin lubricated and prevents rainwater from entering.

However, if the boot deteriorates over time or is left unnoticed for a long time in a condition where it is almost detached from the caliper, the lubrication between the pin and guide may be lost or the pin itself may rust due to moisture. This will affect the sliding direction of the caliper.

One specific problem is brake drag. When the brake lever is released and the piston returns to the inside of the caliper, the caliper may not slide or is difficult to slide, causing the pads on the backside of the rotor (wheel center side) to remain in contact with the rotor, resulting in a dragging condition. If the brakes are dragging on a motorcycle that you ride on a daily basis, you will often feel discomfort when pushing and walking, but some riders still don't notice it.

If dragging symptoms worsen further, it may lead to a "squeal" which is the noise caused by brake rubbing while pushing and driving. If squeal symptom is cured temporarily by pushing caliper along the pin, that is, pushing toward wheel center, it is considered that pin is not lubricated enough. Another cause of brake squeal is lack of grease on pad spring to hold brake pads, or pad grease on the contact surface of caliper piston and pad, but if squeal disappears by pushing caliper itself, lack of grease on the pin is highly probable. In this case, when the brake is applied after the squeal disappears, caliper movement is poor and pad rubbing recurs, so the squeal starts again, you can tell.

It's even more serious when you try to start a motorcycle you haven't ridden in years, and you start pushing and it works, but when you squeeze the lever a little, the brakes lock up completely. The pin is completely rusted and fat in the guide of the caliper, and of course without lubrication, if you hold the lever, the strong hydraulic pressure will push the piston out and pull the caliper itself in. But even if you release the lever and the piston returns, the caliper itself cannot slide back to the original position.

The pin on the caliper support that connects the front fork to the caliper is not just a joint, it is the most important part of a single-piston caliper.

Forcing the rotor when it's not moving properly can cause it to bend.

I tried to use the caliper piston tool but the gap between the caliper and the support is too narrow to get the pawl in properly, I observed the base of the two pins and it looks like each has a rubber boot in it and no cracks.

Fix the caliper support firmly in a vise, spray lubricant in the gap between the pin and caliper, and gradually widen the gap. If you try to pull it out all at once, it will fail, so the key is to be patient and push it out gradually.

The surface of the slide pin that finally came out was covered with red rust. Since the caliper is made of aluminum, the worst thing that could happen is that the rust would unite the caliper, but it is strange that only the pin is rusted while the rest of the support is not rusted at all. The most likely cause is a lack of dehydration from the water that entered through the gap between the boots when the caliper was washed in a bucket.

Rust was removed with a brass brush and polished with sandpaper to restore the surface smoothness. The guide holes on the caliper side were also cleaned with parts cleaner and a rag, and grease was applied to both sides to restore them. Before installing the caliper on the vehicle, make sure that the caliper support inserted into the caliper slides smoothly.

When a single-piston caliper is not moving properly, pushing the caliper body toward the wheel center will temporarily open the caliper and eliminate the drag. However, this method is only a temporary solution to poor lubrication and rusting of the slide pin. Furthermore, if you kick the caliper with your foot or hit it with a rubber hammer when the pin is stuck and locked, the force may bend the brake rotor that the pad is in contact with.

To repair brakes that are dragging so badly that they are difficult to push and walk on, do not try to force the caliper open, but remove the caliper support mounting bolts and then remove the caliper itself by pulling it in the direction of the outer edge of the rotor.

Once the caliper and caliper support has been removed from the front fork, pull the support out of the caliper, but be careful when doing this as there is a risk of bending the slide pin if you pry the support forcibly. Use a brake pad tool or hold the caliper support in a vise and push the caliper out to separate it.

Once the pin is out, countermeasures are applied. The motorcycle I worked on this time had been stored in the same place indoors for about 3 years without being pushed around, and the pin was swollen with red rust and stuck to the inside of the guide. I ground the pin with sandpaper and cleaned the inside of the guide with a rag and cotton swab.

There is no obvious damage to the rubber boot where the pin is inserted, and there is no rust anywhere on the caliper body, rotor or wheel except for the pin, so the condition is not bad. However, if there is no moisture, only the pin will not rust bright red, so I can imagine that it was corroded by the moisture left in the guide before storage.

After the rust was removed and grease was applied to restore it, any symptoms of dragging or locking were eliminated. Many maintenance enthusiasts who regularly check pad levels and clean and rub out caliper pistons may wash the calipers entirely using a mild detergent. If the caliper support is also washed with water, it is possible that water has entered between the pin and guide in the process, so it is useful to pull out the pin and grease it up once in a while.