An internal expanding shoe brake consists of two brake shoes that are pivoted at one end and pushed outward against the inside of a drum brake by a cam at the other end. When the cam rotates, it forces the brake shoe linings out to rub against the inner surface of the rotating drum brake, generating friction to slow the drum's rotation and the wheel it is attached to. The drum encloses the brake mechanism and shoes to protect them from dust and moisture.

1. Introduction
 All braking systems require the use of a rotating (turning) unit
and a nonrotating unit. Each of these units contains braking
surfaces that, when rubbed together, give the braking action.
 Brakes are either external contracting or internal expanding
depending upon how the nonrotating braking surface is forced
against the rotating braking surface.
 The nonrotating unit may be placed inside the rotating drum with
the drum acting as a cover for the braking surfaces. This type of
brake is known as an internal-expanding brake because the
nonrotating braking surface is forced outward against the drum to
produce braking action.
 This type of brake is used on the wheel brakes of cars and trucks
because it permits a more compact and economical construction.

2. Construction
 An internal expanding
shoe brake consists of
two shoes S1 and S2.
 The outer surface of the
shoes are lined with some
friction material (usually
with Ferodo) to increase
the coefficient of friction
and to prevent
wearing away of the metal.
 Each shoe is pivoted at one end about a fixed fulcrum O1 and O2 and
made to contact a cam at the other end.

3. Construction
 When the cam rotates,
the shoes are pushed
outwards against the
rim of the drum.
 The friction between the
shoes and the drum
produces the braking
torque and hence reduces
the speed of the drum.
 The shoes are normally held
in off position by a spring .
 The drum encloses the entire mechanism to keep out dust and moisture.

4. Working
 Now we consider the
forces acting on the
brake when the drum
rotates in the
anticlockwise direction :
 It may be noted that for
the anticlockwise
direction, the left hand
shoe is known as leading or primary shoe
while the right hand shoe is known as trailing or secondary
shoe.

5. Working
 r = Internal radius of
the wheel rim.
 b = Width of the
brake lining.
 F1 = Force exerted by
the cam on
the leading shoe.
 F2 = Force exerted by
the cam on the trailing shoe.

6. Working
 r = Internal radius of
the wheel rim.
 b = Width of the
brake lining.
 F1 = Force exerted by
the cam on
the leading shoe.
 F2 = Force exerted by
the cam on the trailing shoe.