04-02-2020, 11:04 PM
Tony.
Consider a brake drum rotating clockwise, with a brake shoe running from 12 0'clock to 6 0'clock on the right hand side. If the actuator is at 12 0'clock and the shoe pivoted at 6 o'clock then, as the shoe contacts he drum, the drum will tend to pull the shoe in the same direction as it is rotating. Since the shoe can't follow the drum because of the pivot, it is dragged into closer contact with the drum, thus increasing the braking effort. This is known as 'self-servo' action. If the shoe is on the left of the drum (i.e.running from 6 o'clock through to 12 o'clock) but pivoted at 6 o'clock and actuated at 12 o'clock, then the rotation of the drum will have an opposite effect and try to push the shoe away from the drum, reducing the braking effort.
Hope this helps.
Consider a brake drum rotating clockwise, with a brake shoe running from 12 0'clock to 6 0'clock on the right hand side. If the actuator is at 12 0'clock and the shoe pivoted at 6 o'clock then, as the shoe contacts he drum, the drum will tend to pull the shoe in the same direction as it is rotating. Since the shoe can't follow the drum because of the pivot, it is dragged into closer contact with the drum, thus increasing the braking effort. This is known as 'self-servo' action. If the shoe is on the left of the drum (i.e.running from 6 o'clock through to 12 o'clock) but pivoted at 6 o'clock and actuated at 12 o'clock, then the rotation of the drum will have an opposite effect and try to push the shoe away from the drum, reducing the braking effort.
Hope this helps.