Brake calipers for racing machines often incorporate caliper pistons made of aluminum with hard anodizing. For production road motorcycles, hard chrome plating is often applied to steel parts. Since caliper pistons have a great deal to do with the braking performance, control, and lever touch feeling, their surface finish is extremely precise. If you notice any kind of damage to the pistons, you must immediately perform maintenance.
Piston seal area prone to spot rusting
There are a surprising number of cases where point rust or hole rust around the piston seal or in the sliding area between the caliper piston and the caliper body causes the piston to return poorly as a result, which in turn causes the brake to make a dragging noise. Brake calipers of old motorcycles and brake calipers without dust seals do not have good drainage performance, so especially when driving in the rain, just rinsing the area around the caliper vigorously with a water hose and blowing air after returning home will be effective in maintaining the brake performance. This time, I bought parts made by Constructors, an out-of-print motorcycles parts company. I bought one brake piston, one set of seal kit, and two pad shims since it is a W disc.
Use a brake fluid stopper!
Since only the caliper itself is disassembled and cleaned, the brake lines were removed at the flared pipe section and a "fluid stopper" was used to prevent the brake fluid from dripping. In case of vanjo type brake hose, it is better to use a washcloth type fluid stopper. It is a must have special tool for Sunday Mechanic.
Stare at the caliper seal area!
Use a rag to wipe off the brake fluid that has accumulated in the disassembled caliper body. Use the pickup tool to remove the caliper seal. Be careful not to use a screwdriver or similar tool to forcibly remove the seal, as it will scratch the seal groove. Solid deposits often accumulate in the caliper seal groove, and these deposits can significantly reduce the piston's ability to operate. In many cases, these deposits can cause the brakes to make a dragging noise.
Replacement part caliper piston
On the left is a steel brake piston made by Kawasaki. On the right is the new SUS brake piston made by Constructors. The pistons are made of stainless steel, so there is no need to worry about rust. The sliding surface of the piston has been polished and it works well. When we compared the performance of the new stainless steel pistons with the used pistons that were rusted at one point, we were able to see a surprising difference. The rusted pistons were not working as well as they should.
Rubber grease is applied and seals are installed.
Before installing the piston seal, a good amount of rubber grease was applied to improve the operation. The grease used here is Superzoil rubber grease. This grease is especially good between the metal and rubber parts. I also applied a thin layer of rubber grease to the sliding surface on the piston side. If you don't have any rubber grease on hand, apply an appropriate amount of brake fluid before installing. If there is no lubrication, even if the brake fluid is new, it will not work properly.
Must be checked for smooth operation with fingertips
After inserting the piston into the caliper body, make sure it works smoothly. At this point, you can also check if the rubber grease makes a big difference in operation. After the piston is pushed in, hook the dust boot to the groove on the piston side and the outer circumference of the retainer on the caliper body side. Apply the rubber grease to the dust boot with your fingertips.
Tightening torque is very important!
Be sure to use a torque wrench when tightening each part of the caliper. The deformation of the caliper due to over-torque can cause the pads to drag, resulting in noise in many cases. After tightening the caliper, bleed the brake fluid. The air release syringe is very useful for this work.
- Point 1・When you disassemble the caliper, check the condition of the outer circumference of the caliper piston thoroughly!
- Point 2・Remove the sludge accumulated on the caliper piston seal which is transformed by brake fluid and water.
- Point 3・When cleaning the seal groove, be careful not to scratch or damage the inside of the groove.
- Point 4・When disassembling the brake piston and master cylinder, use rubber grease to restore them!
One day, after the motorcycle was finished and I was test riding it, I noticed a dragging noise from the brakes. When I installed the double-disc brakes the other day, I noticed what I thought was the cause of the dragging noise. The braking noise while driving is annoying, but the squeaky noise that occurs when pushing the motorcycle is also annoying. There are many causes of brake noise, but one of the basic areas to check is the brake piston.
During the conversion to the double-disc system, it was noticed that the brake piston on the left side of the standard caliper had rust on the outer circumference of the piston. At the time of the work, there were no replacement parts on hand, so the outer circumference of the piston was temporarily polished and restored. It seemed that perhaps that rust collar was the cause of the dragging noise.
Not only the Kawasaki air-cooled Z we are working on here, but many of the brake calipers from the early 70s, the dawn of disc brakes, had a split left-right construction. In fact, if the torque of the tightening bolts is not properly controlled, the caliper itself can become distorted, resulting in poor performance and a tendency for the piston to drag.
For example, Kawasaki air-cooled Z and Mach series brake calipers have a tightening torque of 30-35Nm on the split portions, so if you don't use a torque wrench you can easily over-torque the caliper, so be very careful. The caliper fastening bolt also serves as a slide guide for the caliper itself, so it is important to check that the caliper bracket with the pads installed works smoothly after the caliper and subassembly are installed. It would be a good idea to check it out before integrating it into the front fork.
In this case, the squeaky noise seemed to be caused by a rust collar that was slightly catching the caliper piston and seal the edge, causing the brake piston to not return properly. By replacing the piston, the current dragging noise disappeared, but as the motorcycles is driven, the noise could be caused by a different cause. Once we are able to overcome these issues, we will be able to enjoy our old motorcycle life even more.
