Troubleshooting guide

24
For more information, visit www.bendix.com or www.foundationbrakes.com • 1-800-AIR-BRAKE (1-800-247-2725)
Slack Adjusters
Slack adjusters are used on foundation drum brakes to
link the brake chamber or actuator and the camshaft. Its
arm is fastened to the push rod with a yoke and its spline
is installed on the foundation brake camshaft. The slack
adjuster transforms and multiplies the force developed
by the chamber into a torque which applies the brakes
via the brake camshaft.
To compensate for the gradual wear on the brake block
lining, automatic slack adjusters are equipped with an
adjusting mechanism. For many years now, the required
standard has been an automatically-adjusting design.
Slack adjuster models are designated by a number
which represents its maximum torque rating (e.g. a type
20 unit is rated for a maximum of 20,000 inch-pounds of
torque). Slack adjusters are available in a variety of arm
confi gurations, lengths and spline types.
The entire slack adjuster operates as a unit, rotating as a
lever with the brake cam shaft, as the brakes are applied
Examples of
Off-set and
Straight Arm
Styles
Manual Slack
Adjuster
Adjustment
Mechanism
Lube
Fitting
Spline
Yoke
Bendix
®
Versajust
®
Automatic Slack
Adjuster
Bendix
®
ASA-5
®
Automatic Slack
Adjuster
or released. The most effi cient braking action is obtained
when the slack adjuster arm travel is approximately
90-degrees and in the recommended range of the
chamber. All Bendix
®
slack adjusters incorporate a
grease fi tting and/or a tapped hole for a lube fi tting.
Automatic Slack Adjusters
Automatic slack adjusters automatically adjust for lining
wear. Bendix brand automatic slack adjusters monitor the
brake-lining-to-brake-drum-clearance, thus eliminating
the possibility of over-adjustment.
The automatic slack adjuster does not require periodic
manual adjustment; however, the unit does provide for
manual adjustment for use in the initial installation and
brake relining.
Important: Extract from Bendix
®
Technical Bulletin
Bulletin No: TCH-005-014
Subject: Automatic Slack Adjusters Not For Manual
Adjustment
The automatic slack adjuster is not designed to function
as a manual adjuster once it is unable to maintain
adjustment automatically.
Automatic slack adjusters should not be manually
adjusted in an effort to correct excessive push rod stroke,
because this condition indicates that a problem exists
with the automatic adjuster, with the installation of the
adjuster, or with related foundation brake components,
which manual adjustment will not fi x.
WARNING: The manual adjustment of automatic slack
adjusters is a dangerous practice that could have serious
consequences, because it can give the operator a false
sense of security about the effectiveness of the brakes,
which are likely to go out of adjustment again soon. Do
not make manual adjustments of an automatic slack
adjuster once it can no longer automatically adjust the
brakes. Manual adjustment DOES NOT fi x the underlying
wheel end adjustment. As soon as possible, have the
vehicle inspected by a qualifi ed technician or consult the
manufacturer’s troubleshooting guidelines to locate and
fi x the actual adjustment problem.
Manual Slack Adjusters
Legacy manual slack adjusters require periodic
adjustment to remain within vehicle specifi cations.
Federal
Regulations require
that commercial motor
vehicles manufactured
after October 20, 1994,
and equipped with air
brakes, have automatic
brake (slack) adjusters
and brake adjustment
indicators (push rod).
The Control System: Slack Adjusters