Dodge 2001 Ram 1500, Owner'S Manual

Page: 304 / 2889

The drum forces both brake shoes to move in the
same direction of rotation. Servo action begins with
the primary brake shoe which begins to wedge (or
wrap) itself against the rotating drum surface. This
force is transmitted equally to the secondary brake
shoe through the adjuster screw and anchor pin. The
net result is that each shoe helps the other exert
extra force against the drum. It is servo action that
creates the wedging (or wrap) effect which produces
increased force on the drum braking surface.
All drum brake assemblies are equipped with a self
adjusting mechanism. The components forming the
mechanism consist of the: adjuster screw, adjuster
lever, actuating lever (11 inch brake), lever return
spring and the adjuster lever spring. The adjuster
lever on the 12 inch brake, is also equipped with a
lever and tension spring.
The adjuster mechanism performs two important
functions. First, is in maintaining proper brake shoe
operating clearance. And second, is to maintain brake
pedal height. The mechanism does so, by adjusting
the shoes in small increments to compensate for lin-
ing wear. The adjustment process is continuous
throughout the useful life of the brake lining.
The adjuster components are all connected to the
secondary brake shoes. Actual adjustment only
occurs during reverse brake stops. Secondary brake
shoe movement (during reverse stops), is what acti-
vates the adjuster components.
In operation, secondary shoe movement causes the
adjuster lever spring to exert pull on the lever. This
pivots the lever away from the adjuster screw teeth.
When the stop is completed and the brakes released,
the adjuster lever pivots back to a normal position. It
is during this return movement of the lever when
adjustment occurs. At this point, the lever comes
back into contact with the adjuster screw teeth as it
moves upward. The lever will then rotate the
adjuster screw one or two teeth as needed for adjust-
ment.
NOTE: The adjustment process requires a complete
stop to actually occur. Rolling stops will NOT acti-
vate the adjuster components. In addition, the
adjuster screws are left and right hand parts and
must NOT be interchanged.
DIAGNOSIS AND TESTING - BRAKE DRUM
The maximum allowable diameter of the drum
braking surface is indicated on the drum outer edge.
Generally, a drum can be machined to a maximum of
1.52 mm (0.060 in.) oversize. Always replace the
drum if machining would cause drum diameter to
exceed the size limit indicated on the drum.
BRAKE DRUM RUNOUT
Measure drum diameter and runout with an accu-
rate gauge. The most accurate method of measure-
ment involves mounting the drum in a brake lathe
and checking variation and runout with a dial indi-
cator.
Variations in drum diameter should not exceed
0.069 mm (0.0028 in.). Drum runout should not
exceed 0.18 mm (0.007 in.) out of round. Machine the
drum if runout or variation exceed these values.
Replace the drum if machining causes the drum to
exceed the maximum allowable diameter.
STANDARD PROCEDURE - BRAKE DRUM
MACHINING
The brake drums can be machined on a drum lathe
when necessary. Initial machining cuts should be lim-
ited to 0.12 - 0.20 mm (0.005 - 0.008 in.) at a time as
heavier feed rates can produce taper and surface
variation. Final finish cuts of 0.025 to 0.038 mm
(0.001 to 0.0015 in.) are recommended and will gen-
erally provide the best surface finish.
Be sure the drum is securely mounted in the lathe
before machining operations. A damper strap should
always be used around the drum to reduce vibration
and avoid chatter marks.
The maximum allowable diameter of the drum
braking surface is stamped or cast into the drum
outer edge.
CAUTION: Replace the drum if machining will cause
the drum to exceed the maximum allowable diame-
ter.
CLEANING
Clean the individual brake components, including
the support plate and wheel cylinder exterior, with a
water dampened cloth or with brake cleaner. Do not
use any other cleaning agents. Remove light rust and
scale from the brake shoe contact pads on the sup-
port plate with fine sandpaper.
INSPECTION
As a general rule, riveted brake shoes should be
replaced when worn to within 0.78 mm (1/32 in.) of
the rivet heads. Bonded lining should be replaced
when worn to a thickness of 1.6 mm (1/16 in.).
Examine the lining contact pattern to determine if
the shoes are bent or the drum is tapered. The lining
should exhibit contact across its entire width. Shoes
exhibiting contact only on one side should be
replaced and the drum checked for runout or taper.
Inspect the adjuster screw assembly. Replace the
assembly if the star wheel or threads are damaged,
or the components are severely rusted or corroded.
BR/BE
BRAKES 5 - 33
DRUM (Continued)