Below is a little history and comparison between standard equipment drum brakes and upgraded hydraulic disc brake systems. As these new 5th wheels get larger, heavier and are driven faster up and down mountain grades, we feel hydraulic disc brakes are an absolute necessity.
Disc brake History, operation and design
Experiments with disc-style brakes began in England in the 1890s; the first ever automobile disc brakes were patented by Frederick William Lanchester in his Birmingham factory in 1902, though it took another half century for his innovation to be widely adopted. The first designs resembling modern disc brakes began to appear in Britain in the late 1940s and early 1950s. They offered much greater stopping performance than comparable drum brakes, including much greater resistance to “brake fade” (caused by the overheating of brake components), and were unaffected by immersion (drum brakes were ineffective for some time after a water crossing, an important factor in off-road vehicles). Disc brakes are also more reliable than drum brakes due to the simplicity of their mechanics, the low number of parts compared to the drum brake, and ease of adjustment
Drum brake operation and design—
Drum brakes are designed to convert kinetic energy into heat energy via the process of friction. This heat is intended to be further transferred to atmosphere, but can just as easily transfer into other components of the braking system.
Brake drums have to be substantial pieces of steel or cast-iron to cope with the forces that are involved which can retain a lot of heat. Heat transfer to atmosphere can be aided by incorporating fins into the design of the drum (see heat sink). However, excessive heating can occur due to heavy or repeated braking which can cause the drum to distort, leading to vibration under braking.
The other consequence of overheating is brake fade. This is due to one of several processes or more usually an accumulation of all of them.
1. When the drums are heated by hard braking, the diameter of the drum increases slightly due to thermal expansion of the material, this means the brakes shoes have to move farther and the brake pedal has to be depressed more.
2. The properties of the friction material can change if heated, creating less friction. This is usually only temporary and the material regains its efficiency when cooled,[1] but if the surface overheats to the point where it becomes glazed the reduction in braking efficiency is more permanent. Surface glazing can be worn away with further use of the brakes, but that takes time.
3. Excessive heating of the brake drums can cause the brake fluid to vapourise, which reduces the hydraulic pressure being applied to the brake shoes. Therefore less retardation is achieved for a given amount of pressure on the pedal. The effect is worsened by poor maintenance. If the brake fluid is old and has absorbed moisture it thus has a lower boiling point and brake fade occurs sooner.
Brake fade is not always due to the effects of overheating. If water gets between the friction surfaces and the drum, it acts as a lubricant and reduces braking efficiency. The water tends to stay there until it is heated sufficiently to vapourise, at which point braking efficiency is fully restored.
Jerry LeMar
Americana 5th wheels