Warner Electric Wheel-Brakes (Std) - Manual (Page 5)

Operation
When the magnet rotates, a trunnion, located on the
back of the magnet, moves the cam. The cam, bearing
on the brake shoe end, moves the brake shoe into
contact with the brake drum. After the toe end of the
brake shoe is forced against the brake drum, the shoe
(being free to float on its support and somewhat flexi-
ble in structure) will tend to follow the drum until the
complete brake shoe assembly is making contact with
the drum. The brake shoe is limited in its travel, howev-
er, since the heel end is forced against an anchor,
which is part of the brake spider assembly.
As the amount of current applied to the magnet is
increased, the attractive force between the magnet and
armature becomes greater. With an increase in attrac-
tive force between magnet and armature, more torque
is developed by the “clutch” and the pressure exerted
by the magnet trunnion upon the brake shoe (through
the cam) increases; and the shoe is pressed tighter into
the drum.
Until the vehicle is brought to a stop, slippage between
the magnet and armature occurs. However, if during a
stop sufficient pressure is built up, slippage between
the magnet and armature ceases and the entire unit
(magnet, armature, brake shoe, and brake drum) will
lock and slide the tire, providing the brake is of proper
capacity for the wheel load.
No brake adjustment is necessary. The magnet move-
ment is sufficient to wear the brake lining down to the
rivet heads if the proper brake shoe to drum clearance
is maintained when new lining is present. When the lin-
ing has worn out, the cams come against a positive
stop (preventing further magnet rotation) preventing the
rivet heads from scoring the drum. Improper clearance
between brake shoe and drum initially will cause the
magnet to reach full travel before completely wearing
out the lining. In either case, as full magnet travel is
reached, a gradual loss of brake power will result.
Thus from the foregoing description, it is readily seen
that the Warner Electric Brake is a simple power-brake.
The amount of power developed being controlled by
the amount of current metered to the magnet by the
brake controls. Maximum power being achieved by an
amount of current approximately equal to that used by
a tail-lite.
How to Break in Trailer Brakes
When the armatures and magnets are new, to prevent
possible damage and to increase their efficiency, the
following steps should be followed during the initial
braking applications:
1. Attain a minimum vehicle speed of thirty miles
per hour and apply trailer brakes only until the
vehicle speed is retarded to approximately fif-
teen miles per hour, then release the brakes
allowing the vehicle to regain speed. DO NOT
LOCK THE WHEELS.
2. Next, drive for about one-half mile without
applying the trailer brakes. Repeat Step No. 1.
3. It will be necessary to follow Steps No. 1 and
2 until you have traveled approximately six
miles.
4. Allow the brakes to run free during the next
four miles. Then apply the brakes to check
their efficiency.
This procedure is also recommended whenever a
wheel has been pulled for maintenance of any kind or
when the trailer has set idle for any extended period of
time.
How to Apply Brakes
A brake is designed for a fixed capacity based upon
wheel load and tire size, and it is mounted in a mini-
mum of space in order to clear springs and frames.
Considering this, it should not be required to handle
more than its own wheel load.
To obtain satisfactory trailer brake performance, the
towing vehicle’s brakes must handle their own load,
and therefore, must be applied simultaneously with the
trailer brakes. Consequently, the towing vehicle’s
brakes and the tractor trailer brake control system
must be kept in good repair to obtain maximum results
from the trailer brakes.
Overloading or using only the trailer brakes to stop the
complete tractor-trailer unit, will cause the heat absorp-
tion capacity of the brake to be exceeded. Hotter
brakes, longer stops, and shorter lining life will result.
5 Warner Electric • 800-825-9050 819-0514