Warner Electric Wheel-Brakes (Std) - Manual (Page 16)

16 Warner Electric • 800-825-9050 819-0514
Check drums for excessive heat checking and scoring.
Heat checking may be a sign of an undersized brake, a
dragging brake, or an unbalanced brake condition in
the tractor-trailer unit. Heat checking will also be
accompanied by excessive brake lining wear. If the
brake drum is scored, check for loose lining rivets or
foreign metal particles imbedded in the lining. Drums
which have excessive heat checking or scoring should
be turned.
Drum and Lining Clearance
Since the electric brake cannot be adjusted to
compensate for drum and lining wear, clearance
between drum and lining is one of the most important
factors governing electric brake operation. This
clearance is best controlled at the initial installation,
during re-lines, and during drum replacement. If proper
clearance between drum and lining is maintained at
these times, the electric brake is so designed that the
lining will be completely worn out by the time the
maximum cam travel is reached. However, if too much
clearance is present initially, maximum cam travel will
be reached before the lining is completely worn out
and a gradual loss of brake power will result. Too little
clearance initially may cause a brake to drag with a
possible wheel lockup, or make it difficult to assemble
the wheel onto the axle. Considerable variation in drum
to lining clearance between brakes on a given unit
could cause unbalanced braking.
Relining Brakes
Brake shoe and lining assemblies as received from
the factory are ground to give a drum to lining
clearance of approximately .020” (.040” on the
diameter) with respect to the nominal brake diameter.
When relining or replacing a drum, the drum bore and
overall lining diameter (Figure 3-9), should be matched
to obtain approximately .020” clearance. Table III will
serve as a guide for obtaining proper clearance.
Caution should be exercised when boring drums and
relining shoes as there is no definite yardstick to follow
as to how much a drum may be oversized. It is
generally recommended that a drum shall not be bored
oversize more than 1/4” on the diameter and that shim
stock thicker than 1/8” shall not be used with riveted
lining. In some operations, such as mountainous
terrain, it is recommended that drums be replaced
before this time. In order that peak brake efficiency be
obtained, use only factory approved and tested lining
as covered by Charts I-26011 and I-26012 in the
replacement parts section of this manual.
Do not weld metal to band ends to compensate for
drum wear, excessive drum to lining clearance, or wear
of brake components.
Always check the brake shoe assembly for worn loose
or greasy lining. If any of these conditions exists,
replace with Warner recommended lining. The high
radial pressures developed by the brakes will cause too
soft a lining to wear rapidly, often causing damage to
the drum and the brakes to fade under heat. Where
greasy lining is encountered, inspect and replace
grease seals. If enough grease is present, it may be
necessary to remove the grease guard or armature
adapter and clean grease from wheel and drum. When
replacing the grease guard or armature adapter, a thin
coating of “Permatex” or other suitable sealer must be
used between adapter and drum. Surface grease on
lining, drum braking surface, magnet, and armature can
be removed with carbon tetrachloride or other suitable
solvent. However, if grease has penetrated lining or
magnet facing, they must be replaced since grease will
seep to the surface under heat causing weak brakes.
Figure 3-9
Measuring Band Size with Outside Micrometers