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The information set forth below is the approach used in our shop.
There is a high probability that one of the conditions set forth below is causing your drum to bind as you try to remove it. The simplest solution is to use your brake spoon develop the maximum amount of spacing between the brake shoe and the drum.
If that doesn't work, on occasion we've had to use a chisel or a cutting torch to remove the drum. It is very seldom that such drastic measures must be taken but it has happened.
Surface/Heat Checks/Cracked Drum/Out-Of-Round Drum
Brake drums act as a heat sink. They absorb heat and dissipate it
into the air. As drums wear from normal use or are machined, their
cooling surface area is reduced and their operating temperatures
increase. Structural strength also reduces. This leads to
overdistortion, which causes some of the drum conditions covered here.
Scored Drum Surface
A scored drum surface shows a scored drum surface. The most common
cause of this condition is buildup of brake dust and dirt between the
brake lining and drum. A glazed brake lining, hardened by high heat or
in some cases by very hard inferior grade brake lining, can also groove
the drum surface. Excessive lining wear that exposes the rivet head or
shoe steel will score the drum surface. If the grooves are not too deep,
the drum can be turned.
Example of a scored brake drum. Courtesy of Wagner Brake Products.
Bell-mouthed drum shows a distortion due to extreme heat and braking
pressure. It occurs mostly on wide drums and is caused by poor support
at the outside of the drum. Full drum-to-lining contact cannot be
achieved and fading can be expected. Drums must be turned.
Example of a bell-mouhed brake drum. Courtesy of Wagner Brake Products.
A concave drum exhibits an excessive wear pattern in the center area
of the drum brake surface. Extreme braking pressure can distort the shoe
platform so braking pressure is concentrated at the center of the drum.
Examples of concave and convex brake drums. Courtesy of Wagner Brake Products
A convex drum exhibits excessive wear at the closed end of the drum.
It is the result of excessive heat or an oversized drum, which allows
the open end of the drum to distort.
Hard Spots On The Drum
This condition in the cast-iron surface, sometimes called chisel
spots or islands of steel, results from a change in metallurgy caused by
braking heat. Chatter, pulling, rapid wear, hard pedal, and noise
occur. These spots can be removed by grinding. However, only the raised
surfaces are removed, and they can reappear when heat is applied. The
drum must be replaced.
Threaded Drum Surface
An extremely sharp or chipped tool bit or a lathe that turns too fast
can result in a threaded drum surface. This condition can cause a
snapping sound during brake application as the shoes ride outward on the
thread, then snap back. To avoid this, recondition drums using a
rounded tool and proper lathe speed. Check the edge of the drum surface
around the mounting flange side for tool marks indicating a previous
rebore. If the drum has been rebored, it might have worn too thin for
use. Check the diameter.
Heat checks are visible, unlike hard spots that do not appear until
the machining of the drum. Extreme operating temperatures are the major
cause. The drum might also show a bluish/gold tint, which is a sign of
high temperatures. Hardened carbide lathe bits or special grinding
attachments are available through lathe manufacturers to service these
conditions. Excessive damage by heat checks or hard spots requires drum
Example of a heat checked and over-heated brake drum. Courtesy of Wagner Brake Products.
Cracks in the cast-iron drum are caused by excessive stress. They can
be anywhere but usually are in the vicinity of the bolt circle or at
the outside of the flange. Fine cracks in the drums are often hard to
see and, unfortunately, often do not show up until after machining.
Nevertheless, should any cracks appear, no matter how small, the drum
must be replaced.
Drums with eccentric distortion might appear fine to the eye but can
cause pulling, grabbing, and pedal vibration or pulsation. An
out-of-round or egg-shaped condition is often caused by heating and
cooling during normal brake operation. Out-of-round drums can be
detected before the drum is removed by adjusting the brake to a light
drag and feeling the rotation of the drum by hand. After removing the
drum, gauge it to determine the amount of eccentric distortion. Drums
with this defect should be machined or replaced.
Measure the inside diameter of the drum in several spots to determine out-of-roundness.An out of round or tapered drum prevents accurate brake shoe adjustment prevents not only difficult removal but also can cause excessive wear of other brake parts; excessive tire wear; and, a pulsating brake pedal.
All the best