(similar to that shown in Fig. 9) will be equipped with bushings
which are serviceable. Replaced bushings are to have a
clearance of .076-.127 mm (.003-.005 in.) between bushing
CAMSHAFT, BUSHINGS AND SEALS
The camshaft is actuated by movement of slack adjuster. The
rotating movement of cam forces shoe rollers away from
cam, thus forcing shoes into contact with drum.
Removal procedure for camshaft assembly is covered in Brake
Disassembly procedure. When removing camshaft from
backing plate or spider, note position of spacing washers to
assure correct reinstallation.
Do not remove camshaft bushings from spider and/or
mounting bracket unless replacement is necessary.
Do not interchange right and left hand camshafts.
Removal of brake chamber bracket will be required to replace
the bushings in some instances.
To check bushings to determine if replacement is required,
insert the camshaft in the bushing and check side play. If
more than .5080 mm (.020") on Wagner or Eaton brakes or
.7620 mm (.030") on Rockwell brakes, the bushings need
Install new bushings with a suitable tool like that shown in Fig.
Apply IH 251 HET grease or equivalent NLGI #2 multi-purpose
lithium grease to outside diameter of bushings to assist in
pushing them into position.
Fig. 21 Recommended Type of Camshaft
Bushing Removing Tool
A Bushing Outside Diameter
B Bushing Inside Diameter
C Bushing length
D Suitable Length
Install new seals with lip of seal toward slack adjuster (Fig.
Fig. 22 Brake Chamber Bracket Seal Installation
Brake chambers (Fig. 23) transform energy of compressed air
into mechanical force and motion to apply brakes. One
chamber is used at each wheel to operate brakes.
Air pressure entering the brake chamber (Fig.
23) behind the diaphragm forces the diaphragm and push rod
outward, rotating slack adjuster, brake camshaft and cam
applying the brakes. The higher the air pressure admitted to
chamber, the greater the force pushing brake shoes against
When air pressure is released from brake chamber, brake
shoe return springs and brake chamber release spring return
shoes, cam, slack adjuster and brake chamber back to the
The brake chamber consists of two dished metal sections;
namely, pressure plate assebly and non-pressure plate,
separated by a rubber diaphragm, all of which are held
together by a metal two-segment clamp. In front of the
diaphragm are the push rod, push rod spring and retainer (Fig.
Several types of spring actuated type parking brakes are used
in conjunction with or are attached to brake chambers while
others replace the entire brake chamber.
The purpose of auxiliary spring brakes is to provide an
emergency brake which will stop the vehicle if air pressure
These spring brake systems are covered in PARKING BRAKE
section of the Service Manual.
Refer to the respective section pertaining to
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