The brake cable outer casing, also known as the brake cable housing or brake cable sheath, is a protective covering that encloses the inner brake cable. It serves several important functions in a motorcycle's braking system.

1. Protection: The outer casing provides protection to the inner brake cable from external elements such as dirt, moisture, and debris. It helps prevent contamination and damage that could affect the smooth operation of the brake cable.

2. Durability: The brake cable outer casing is made of a durable material, typically plastic or rubber, that can withstand the rigors of motorcycle use. It is designed to resist wear, abrasion, and environmental factors like heat and UV radiation.

3. Flexibility: The outer casing is flexible to allow for smooth movement of the inner brake cable. It should have enough flexibility to follow the routing of the cable and accommodate the natural movement of the handlebars and suspension.

4. Friction reduction: The inner brake cable slides within the outer casing when the brake lever is actuated. The outer casing is often lined with a low-friction material, such as nylon or Teflon, to reduce friction and ensure smooth cable operation.

5. Cable organization: The outer casing keeps the inner brake cable organized and prevents it from tangling or getting entangled with other components or moving parts of the motorcycle.

Over time, the brake cable outer casing can wear out, become damaged, or lose its effectiveness. Signs of a worn-out or damaged outer casing may include cracks, fraying, or compression of the casing. If any of these issues are detected, it is crucial to replace the outer casing to maintain safe and reliable braking performance.

When replacing the brake cable outer casing, it is important to choose a casing that matches the specifications of the original casing in terms of size and material. The new casing should be cut to the appropriate length and securely installed using proper cable routing techniques.

Regular inspection and maintenance of the brake cable outer casing, along with the inner brake cable, are essential to ensure optimal braking performance and rider safety.