4-38. DESCRIPTION OF BRAKES (Cont)
d. Internal Brakes.
The internal brakes are located within
the brake drums and are supported by
the backing plates which are riveted to
flanges on the axles. Camshaft mounting
brackets, riveted to the back of the back-
ing plates, carry the brake camshafts on
Each internal brake has two brake shoes, the outer surfaces of which are fitted with brake
linings. Each shoe is anchored at one end on an eccentric anchor pin on which it pivots.
The other end of each shoe is free to be pushed out or pulled.
An S-shaped cam on the end of the camshaft is mounted between the free ends of the two
shoes. Rotation of the cam forces the shoes out causing the brake linings to contact the
A brake shoe tension spring, hooked on spring anchor pins, near the free ends of the brake
shoes, retracts the shoes from the drum and holds them in a retracted position until the
brakes are applied again.
The free ends of the brake shoes are fitted with follower rollers which ride on the S-shaped
cam. The contour of the cam is so designed that the positions of the brake shoes with relation
to the drum are determined by the points on which the cam follower rests on the cam. Minor
adjustment of the brake (para. 4-39) adjusts the cam in the proper position to eliminate
excessive movement when the brakes are applied.
The eccentric anchor pins at the pivoted ends of the brake shoes relate the brake shoe arc
to the contour of the brake drum.
The internal brakes are the self-center-
ing type. This type of brake has two
identical brake shoes and two identicaI
wheel cylinder assemblies. The brake
shoes are arranged with the toes oppo-
site each other on the brake drum dia-
meter. Each double-end wheel cylinder
is placed between the toe of one brake
shoe and the heel of the other brake
shoe. The brake shoes are always for-
ward-acting and independently actuated
in the direction of drum rotation. The
brake shoes are anchored at either toe
or heel, depending on the direction of
rotation of the drum.
(All models except M127)