I. Hydraulic Brake Fluids:
Two types of fluids are typically used in braking systems; DOT Brake Fluid and Mineral Oil. The two groups have different base chemical compositions and properties and should not be mixed or substituted for in a brake system. Mixing or substituting these types of fluids will destroy rubber and plastic components within the system. It can also alter the performance characteristics of the brake system.
A. DOT Brake Fluids
DOT brake fluid is approved by the Department of Transportation for use in brake systems and is required to meet certain performance criteria, mostly consistent performance within a specified temperature range. DOT 3, 4 and 5.1 fluids are hygroscopic (water absorbing) glycol based fluids. These fluids absorb water at a rate of 2-3% per year. The result of this is a lower boiling point of the fluid because it is diluted with water. Brake fluid will not boil while under pressure. The automotive industry and all high end motorsports use DOT fluid for their braking systems. DOT 5 brake fluid is silicon based and should not be mixed with the glycol based fluids.
B. Mineral oil
Mineral oils are also used in brake systems but are not controlled by any specific standards. Mineral oil does not absorb water and can break down with time and heat. Low ambient temperatures will cause a mineral oil to congeal and the system to have sluggish performance (<20ºF). Some mineral oils are more environmentally friendly than DOT Brake Fluid, however oil is still an oil and should be disposed of properly.
II. Hydraulic Hose and Fittings
A. Hose Construction – Hose construction is typically composed of three layers:
- Inner Tube – Teflon tubing designed to hold the fluid. Teflon does not react to the various fluids and provides good physical properties for the hose.
- Aramid Woven Layer – Commonly referred to as Kevlar, this woven layer provides the structure for the hose to contain the high brake pressures generated by the master cylinder. The weave is flexible, and yet keeps the inner tube from expanding and or bursting under pressure. Aramid layers can match the expansion and burst performance of a stainless steel hose without adding un-necessary weight. Aramid can also be cut to length using household tools and re-assembled with standard hose fittings.
- Outer Casing – A thin coating of plastic material to reduce the abrasion and wear on the Aramid layer as well as protect the frame and fork the hose is routed on.
B. Hydraulic Hose Performance Characteristics
- Expansion – The amount that a hose expands (volumetric) will affect the modulation of the system. If not properly designed, stroke will be used up to expand the hose instead of generate brake power.
- Kink Resistance – Hoses must be able to resist kinking or cracking even in cold temperatures. They also must be flexible enough to easily route on a frame or fork and flex with the suspension as it goes through its travel.
- Abrasion Resistance – Hoses must be able to stand up to wear induced from vehicle vibration as well as debris.
C. Mechanical cable and housing
Mechanical brakes utilize cable and housing to transfer the input from the handlebar lever to the caliper. Cables and housing have a few disadvantages compared to a hydraulic hose.
- Cable Stretch – Brake cables will stretch over time and require the tension to be readjusted for consistent brake setup.
- Efficiency Loss – Cable sliding within housing creates additional drag on the system especially over long lengths and in areas where the cable is bent for routing purposes. This drag must be overcome by additional input force and reduces the efficiency of the system. When the cables and housing become contaminated with dirt and grit this increases the amount of drag. It is important to keep brake cables and housing clean for optimal mechanical disc brake performance.
D. Mount Hardware
- Mount Bolt – 5mm Hex Cap Screw – M6 X 1.0mm Thread – 18.4 mm length (Some alternate lengths exist for special applications)
- Disc Screws – T25 Torx Head – M5 X 0.8mm Thread – 10 mm length .
- Mount Brackets – Mount brackets are designed to fit a standard caliper to a variety of rotor sizes and hubs. Hayes Brake utilizes one caliper standard and a variety of mount brackets to fit to any application.