Hydraulic clutch lever touch is bad! In such a case, let's check not only the master but also the release!

Hydraulic clutches, which are often used in large vehicles, are attractive because they do not require play adjustment or lubrication as wire clutches do. However, they are not maintenance-free. As with hydraulic brakes, periodic brake fluid changes are essential, and if there is any discomfort in the operability of the clutch lever, the master cylinder and release should also be looked at.

Another advantage of hydraulic clutches is that there is no need to take wire layout into consideration

The clutch wire of a wire-type clutch varies greatly in operability depending on how it passes through the gap between the meter and the front fork. If the clutch lever becomes strangely heavy after the front fork is removed for greasing the steering stem bearing, it is important to review the wire layout. With a hydraulic clutch, there is no need for such subtle adjustments. As with hydraulic disc brakes, Pascal's theorem, which is based on the piston area ratio of the master cylinder and release, ensures that the operating feel is always constant, and the hydraulic path using steel pipes allows for a high degree of freedom in layout because there are no problems even if the path is bent at right angles. Also, by utilizing the servo effect based on Pascal's theorem, a powerful clutch spring can be operated with a light lever operation. The weak point of this type of clutch is that it is more costly and heavier than a mechanical wire type clutch due to the increased number of parts, but the fact that it is used in many types of vehicles, especially heavy-duty vehicles, is proof of its proven track record and reliability.

Kawasaki GPZ900R Ninja clutch release with three bolts on the drive sprocket cover. Shift position numbers are cast into the release body.

The rubber hose extends 200mm from the clutch release, but the hose along the frame from there to the master cylinder is made of steel. The steel hose is thinner than the rubber hose and has many advantages, such as greater flexibility in layout and not being crushed by the gasoline tank.

Like the brake calipers, the clutch release is susceptible to heat and moisture.

Although actions such as cleaning and lubricating the wires are not necessary, hydraulic clutches also require maintenance. As with hydraulic disc brakes, a fluid change every two years is mandatory. The hydraulic fluid used in brakes and clutches is the same glycol-based liquid, and instead of boiling at high temperatures, it absorbs moisture. It is true that in the case of brake fluid, moisture contamination and lowering of the boiling point directly leads to performance degradation during braking, whereas clutch fluid, which does not rise as high in temperature as brake fluid, is less affected by heat. However, heat from the engine is transferred to the clutch release mounted on the crankcase, and if the engine is driven in the rain during touring, moisture will adhere to the release. Also, as with hydraulic brakes, the clutch master cylinder and clutch release piston become dirty and worn as they operate, requiring cleaning and parts replacement. The clutch release piston has a stroke of only a few millimeters and, like the caliper piston, moves forward slightly as the friction plate wears, returning to its original position by the elasticity of the rubber piston seal. While this action has the advantage that the lever play remains unchanged, the fluid that remains on the exposed portion of the piston can deteriorate and crystallize, or absorb moisture, causing rust on the piston's hard chrome plating and increased friction loss during operation. Fluid crystallization and contamination can occur even when the clutch fluid is changed regularly. In addition, the fluid in the clutch release may not be completely replaced by simply draining the bleeder plug in the same way that air is drained, and it is not uncommon for the fluid from the master cylinder and bleeder plug to be clear and colorless, but the fluid inside the release to be cloudy like coffee milk. It is not uncommon for the fluid from the master cylinder and bleeder plug to be clear and transparent, but the inside of the release to be cloudy like coffee milk. That is why regular disassembly and cleaning of the clutch release is essential.

Remove the clutch release by pulling out the three bolts. As with the brake caliper, there is a rubber seal between the piston and cylinder, so fluid will not leak out. On the other hand, if it is seeping from here, the oil level in the master cylinder's check window should be lowered.

When the clutch lever is gripped, the piston should gradually protrude and foreign matter can be seen in the gap between the piston and the cylinder. The more dirt that accumulates, the worse the piston movement becomes, so cleaning is necessary to prevent problems.

There is a spring on the back of the release piston that can pop out under tension when the clutch lever is operated to push the piston out to some degree. To prevent the fluid from splashing onto the painted surface, wrap it in a rag and work with it.

Even a light scrubbing with a paper rag will result in contamination. It also accumulates inside the seal groove where the piston seal is incorporated, so remove the seal and clean it thoroughly.

A hand honing tool will make cleaning the clutch cylinder easier.

The construction of the clutch release and brake caliper is similar, but while the brake caliper's piston seal and dust seal are built into the caliper side, the seal on the Kawasaki GPZ900R Ninja clutch release shown here is on the piston side, and the release side The release side is a simple cylindrical shape without ring grooves. A honing tool is useful for cleaning these parts. A honing tool is a tool that allows multiple grinding wheels to scrape and grind the inside of a cylindrical part, making even and even contact rather than pressing sandpaper or compound against the inside of the part with fingertips. Honing stones vary in grain size, but it is important to select the finest possible grit for cleaning purposes to avoid unnecessary scratches. After attaching the honing tool to an electric drill and applying outward tension to the grinding wheel according to the cylinder bore, the tool is rotated inside the clutch release, which has been sprayed with a generous amount of anti-rust lubricant. Adjust the rotating speed and tension of the grinding wheel while scraping off any dirt or foreign matter and checking to make sure not to cause unnecessary damage to the cylinder inner surface. While brake calipers with sealing grooves require removal of dirt from the grooves, the cylinder of the clutch release is a simple cylinder, so the process is quick and easy, taking only a few seconds. After cleaning the release piston with a mild detergent and metal polish, replace the piston seal with a new one if necessary, and assemble it, and you will be surprised at how smooth the stroke feels.

Altered clutch fluid has crystallized and accumulated on the inner wall of the clutch release cylinder. Most of it can be removed by soaking it in hot water and scrubbing with a mild detergent and a toothbrush, but if the rough surface cannot be removed, a honing tool can be effective.

Attach a honing tool to an electric drill to polish the cylinder's inner surface. The work is far more efficient than scrubbing with a brush or sandpaper, and it is harder to get an even finish.

However, too much grinding is a waste of time, so it is important to start with a fine-grained grinding stone and set the tension to be applied to the cylinder's inner surface at a low level to see how it goes.

The surface was finished smooth despite the worm-like corrosion marks. The clutch release itself needs to be replaced as it is gouged by corrosion and can cause fluid leakage.

Apply rubber grease suitable for lubricating metal and rubber to the cleaned piston. Silicone grease is also acceptable.

Push the piston in, being careful not to turn the lip of the piston seal over on the cylinder end face. The engine runs much smoother than it did before cleaning.

Attach the clutch release to the sprocket cover, being careful to tighten the three bolts evenly. Since the hose was removed from the clutch release this time, brake and parts cleaner was injected inside the hose to clean it when replacing the fluid.

Don't forget to clean the master cylinder when changing the fluid.

To clean the clutch release, the release is removed from the engine, which inevitably means replacing all the fluid in the master cylinder, clutch hose, and clutch pipe as well. At that time, if possible, you should remove the clutch hose from the clutch master cylinder and spray brake and parts cleaner inside, then blow air to clean the inside, and remove the master cylinder piston and clean the inside of the cylinder as well. If the inside of the clutch release is dirty, it is reasonable to assume that the master cylinder is also reasonably dirty, and if there is a pool of deteriorated fluid at the bottom of the reservoir tank, cleaning is a must. Hydraulic clutches have a strong clutch spring, so even if there is some friction loss when the release piston is actuated, it rarely causes the clutch to go into a half-clutch state. However, if the response of the piston to the clutch lever is poor, it may cause discomfort during clutch operation. If you feel that the hydraulic clutch is difficult to recognize the half clutch or that the clutch is too abrupt, we recommend that you check the condition of the clutch release and the master cylinder.

Dirty black fluid has settled in the master cylinder reservoir tank. Injecting new fluid in this condition will only cause the contamination to spread, so it should be cleaned beforehand.

Wipe the bottom of the tank with tissue paper or a rag, then clean it with brake and parts cleaner. If you want to add another step, it is even better to disassemble the master cylinder and clean the piston and cup seal area as well.

Connect a hose to the clutch release and inject brake fluid.

As with the brakes, bleed air from the bleeder plug and rinse the plug and surrounding area with water to complete the job.

Go to  (17)