Bendix Commercial Vehicle Systems VERSAJUST AUTOMATIC SLACK ADJUSTER User Manual
®
Bendix® Versajust™ Automatic Slack Adjuster
SD-05-4630
DESCRIPTION
The Bendix® Versajust™ automatic slack adjuster is
designed for use on cam-actuated drum brakes, the
type in use on most highway vehicles. Like a manual
slack adjuster, the Versajust™ slack adjuster multiplies
and transforms the linear force of the air actuator into
a rotational force, or torque, which is used to apply the
foundation brake. In addition, the Versajust slack adjuster
automatically adjusts the clearance between the brake
lining and drum to compensate for wear.
A variety of Bendix Versajust slack adjuster congurations
are offered, including both straight arm and 5/8" yoke offset
models. The Versajust slack adjuster is offered in arm
lengths of 5, 51/2 and 6 inches, and worm gear splines to
accommodate the standard 11/4" and 11/2" SAE 10C-, 24-,
and 28-tooth splines.
Either of two yoke designs (easy-on and quick connect) in
combination with an external manual adjuster hex provides
for convenient installation and maintenance of the Bendix
Versajust slack adjuster. Note: The manual adjuster
hex is intended for use during installation. CAUTION:
Automatic slack adjusters should not be adjusted
manually to correct excessive push rod stroke.
OPERATION
GENERAL
The automatic adjustment provided by the Bendix Versajust
slack adjuster results in consistent brake-lining-to-drumclearance and brake actuator stroke. The key to its
operation is the ability to complete the brake adjustment
during the early part of each brake application and to cease
adjusting as resistance to brake cam rotation begins to
build. This aspect of the adjuster mechanism’s operation
prevents over-adjustment caused by lining compression,
actuator bracket deection, drum and foundation brake
component distortion, or brake component wear.
The Versajust slack adjuster incorporates a clutch-type
adjuster mechanism that continuously adjusts – in very
small increments – as lining and drum wear occurs. The
adjustments made by the Versajust slack adjuster are,
therefore, not in specic increments relative to actuator
stroke.
YOKE
Compatible with
Bendix® ASA-5®
Automatic Slack
Adjusters
MANUAL
ADJUSTMENT
HEX
LUBE FITTING
FIGURE 1 - BENDIX
ADJUSTER
®
VERSAJUST
™
AUTOMATIC SLACK
YOKE
PIN
LINK
PIN
LINK
BOOT
WORM
GEAR
Note that the Versajust automatic slack adjuster is
compatible with Bendix® ASA-5® automatic slack adjusters.
Therefore, it is acceptable to have a Versajust automatic
slack adjuster on one side of the axle and an ASA-5
automatic slack adjuster on the other side of the same axle.
BRAKE APPLICATION
When the brakes are applied, the linear travel of the brake
actuator’s push rod causes the Versajust slack adjuster to
rotate the foundation brake camshaft, which in turn begins
to force the brake shoes into contact with the drum. When
the Versajust slack adjuster rotates, the yoke assembly
pivots on the yoke pin, causing the link to be pulled upward.
The “teeth” on the link mesh with the adjuster mechanism
pinion. As the link is pulled, it travels rst through its free
play and then causes the pinion to rotate. Rotation of the
pinion is transmitted through the clutch spring to the worm
1
GENERAL SAFETY GUIDELINES
WARNING! PLEASE READ AND FOLLOW
THESE INSTRUCTIONS TO AVOID
PERSONAL INJURY OR DEATH:
When working on or around a vehicle, the following
general precautions should be observed at all times.
1. Park the vehicle on a level surface, apply the
parking brakes, and always block the wheels.
Always wear safety glasses.
2. Stop the engine and remove ignition key when
working under or around the vehicle. When
working in the engine compartment, the engine
should be shut off and the ignition key should be
removed. Where circumstances require that the
engine be in operation, EXTREME CAUTION
should be used to prevent personal injury resulting
from contact with moving, rotating, leaking, heated
or electrically charged components.
3. Do not attempt to install, remove, disassemble
or assemble a component until you have read
and thoroughly understand the recommended
procedures. Use only the proper tools and observe
all precautions pertaining to use of those tools.
4. If the work is being performed on the vehicle’s
air brake system, or any auxiliary pressurized air
systems, make certain to drain the air pressure
from all reservoirs before beginning ANY work
on the vehicle. If the vehicle is equipped with
a Bendix® AD-IS® air dryer system or a dryer
reservoir module, be sure to drain the purge
reservoir.
5. Following the vehicle manufacturer’s recommended
procedures, deactivate the electrical system in a
manner that safely removes all electrical power
from the vehicle.
6. Never exceed manufacturer’s recommended
pressures.
7. Never connect or disconnect a hose or line
containing pressure; it may whip. Never remove
a component or plug unless you are certain all
system pressure has been depleted.
8. Use only genuine Bendix® brand replacement
parts, components and kits. Replacement
hardware, tubing, hose, ttings, etc. must be of
equivalent size, type and strength as original
equipment and be designed specically for such
applications and systems.
9. Components with stripped threads or damaged
parts should be replaced rather than repaired. Do
not attempt repairs requiring machining or welding
unless specically stated and approved by the
vehicle and component manufacturer.
10. Prior to returning the vehicle to service, make
certain all components and systems are restored
to their proper operating condition.
11. For vehicles with Automatic Traction Control (ATC),
the ATC function must be disabled (ATC indicator
lamp should be ON) prior to performing any vehicle
maintenance where one or more wheels on a drive
axle are lifted off the ground and moving.
and shaft. Worm and shaft rotation results in worm gear
rotation, which in turn adjusts (or repositions) the brake
camshaft.
When the foundation brake shoes contact the drum, the
camshaft begins to resist rotation and friction between the
worm gear and worm builds, preventing further rotation
of the worm. Brake adjustment ceases at this point and
further rotation of the Bendix® Versajust™ slack adjuster will
cause the pinion and clutch spring to slip. The “free play”
between the link teeth and pinion results in a predetermined
lining-to-drum clearance.
BRAKE RELEASE
When the brake application is released, the brake
actuator push rod returns the Versajust slack adjuster
to the released position. During release, the Versajust
slack adjuster rotates back toward the actuator causing
the brake camshaft to again rotate, but in the opposite
direction, and the brake shoes begin to move away from
the drum. As the Versajust slack adjuster rotates back to
the release position, the yoke again pivots causing the link
to be pushed downward into the slack adjuster body. The
“free play” between the link teeth and pinion is taken up
during the initial part of the release. Continued movement
2
of the Versajust slack adjuster toward the released position
causes the link to rotate the pinion. The anti-reverse spring
prevents counterclockwise rotation of the shaft and worm,
causing the pinion and clutch spring to slip. The gripping
action of the anti-reverse spring – and slippage of the clutch
spring during release – is due to the direction of the coil
windings of each.
YOKE DESIGNS
The Bendix® Versajust™ slack adjuster may be equipped
with either of two yoke designs. Both are designed to permit
installation or removal of the slack adjuster, along with its
yoke body and its attached adjusting linkage.
The brake actuator push rod must thread into the adapter a
minimum of 1/2 inch and must not extend more than 7/64 inch
beyond the other end of the adapter. The yoke adapters
(quick connect & easy-on) have either a 1 or 11/4 inch hex
to allow tightening of the brake actuator push rod jam nut.
EASY-ON YOKE (REFER TO FIGURE 2)
The easy-on yoke assembly consists of an adapter which
is threaded internally to match the push rod threads and
externally to match female threads in the yoke. A special
extended yoke adapter is also available as a separate
service item. The extended adapter is 1/2 inch longer than
the standard, and is primarily intended for use when the
existing brake actuator push rod is too short.
PUSH ROD
15/16"
JAM NUT
YOKE
A. With the brake chamber in the released position,
place a square (or an equivalent object) so that one
edge is parallel to the actuator push rod, while the
other edge bisects the brake camshaft. Measure
the distance from the push rod end to the vertical
edge of the square and compare it to the values in
Figure 4.
BR AKE ACT U ATO R
PUSH ROD
SQUARE
MOUNTING
STUD
ADAPTER
FIGURE 2 - EASY-ON YOKE ASSEMBLY
3
/8" OUT
QUICK-CONNECT YOKE
The adapter bushing in this case is threaded internally to
match the push rod, but is designed to slide into the yoke.
A retainer ring is used to secure the adapter bushing in the
yoke. (Refer to Figure 3.)
PUSH ROD
JAM NUT
MOUNTING
STUD
ADAPTER
BUSHING
FIGURE 3 - QUICK-CONNECT YOKE ASSEMBLY
RETAINING RING
1"
FLUSH
YOKE
INITIAL INSTALLATION PREPARATION
1. If necessary, carefully remove the manual or automatic
slack adjuster currently installed, including the brake
chamber yoke assembly.
2. Before mounting the Bendix® Versajust™ slack adjuster
on the camshaft, check the brake chamber push rod
length to determine whether shortening or replacement
is required. To accomplish this:
DI STANCE
"A"
MOUNTING
STUD
"A" Std.
Slack Adjuster
Arm Length
5" 1
51/2" 115/16" - 33/16" 27/16" - 311/16"
6" 1
FIGURE 4 - MEASURING THE BRAKE ACTUATOR PUSH
ROD
Quick Connect or
Easy-On Adapter
15
/16" - 31/32" 27/16" - 317/32"
3
/16" - 33/16" 111/16" - 311/16"
"A" Extended
Easy-On Adapter
B. If the measurement is less than the minimum shown
in Figure 4, the brake actuator push rod must be
shortened. If the measurement is greater than
the maximum values, the brake actuator push rod
may require replacement. The extended adapter –
available as a separate service part (5/8"-18 pc. no.
297700 and 1/2"-20 pc. no. 297701) – may avoid
the need to replace the brake actuator push rod.
The extended adapter is available for the easy-on
yoke assembly only. Note: Installing any other
type of push rod extender is not recommended.
These devices may loosen over time and result in
an improperly adjusted brake.
3. Inspect the foundation brake, brake chamber, and
related components. Make certain the camshaft
bushings and seals are not excessively worn. Lubricate
the camshaft bushings. Check the brake chamber
bracket for cracks and excessive corrosion. The brake
actuator push rod should not be loose or bent, and the
return spring should be rm. Replace parts that are
suspect.
4. Wire brush the foundation brake camshaft to loosen
contamination and wipe clean. Depending on
3
Loading...