Bendix Commercial Vehicle Systems PIGGYBACK SPRING BRAKE User Manual
®
Bendix Piggyback Spring Brake
SERVICE PUSH-ROD
SERVICE
CHAMBER
SD-02-4500
SERVICE
DIAPHRAGM
FIGURE 1 - BENDIX PIGGYBACK SPRING BRAKE
DESCRIPTION
The Bendix Piggyback Spring Brake is made up of a
conventional brake chamber and an emergency or parking
spring mechanism for use on vehicles equipped with cam
foundation brakes. The S pring Brake Actuator provides: (1)
Service Braking, (2) Parking and (3) Emergency Braking.
The actuator can be piped with various system arrangements
to be automatically or manually applied under emergency
braking conditions.
The spring brake is a diaphragm type actuator which converts
the energy of air pressure into mechanical force. The
diaphragm is held between the pressure plate and nonpressure plate by a two piece clamp ring.
Different size brake chambers are identified by numbers
which specify the effective area of a diaphragm. For example,
a T ype 30/30 Spring Brake has 30 square inches of ef fective
area on each diaphragm.
The standard diaphragm material is a compound of natural
rubber with a fabric interior of nylon.
PIGGYBACK CHAMBER
PREVENTIVE MAINTENANCE
Important: Review the warranty policy before performing
any intrusive maintenance procedures. An extended warranty
may be voided if intrusive maintenance is performed during
this period.
Because no two vehicles operate under identical conditions,
maintenance intervals will vary . Experience is a valuable guide
in determining the best maintenance interval for a vehicle.
WARNING!
Piggyback Spring Brake Chambers contain a loaded
compression spring. Property damage, serious injury
or death may occur if instructions are not followed
completely.
Every 300 operating hours, 8,000 miles, or one (1) month:
1. Check push rod travel and adjust travel at the slack
adjuster if needed. Push rod travel should be as short
as possible without the brakes dragging. Excessive push
rod travel reduces braking efficiency , shortens diaphragm
life, gives slow braking response and wastes air.
1
2. Check push rod to slack adjuster alignment from release
to full stroke position to be sure the push rod moves out
and returns properly without binding at the non-pressure
plate hole or with other structures. Also check the angle
formed by the slack adjuster arm and push rod. It should
be greater than 90 degrees when the chamber is in the
released position and approach 90 degrees at maximum
readjustment stroke.
3. Check tightness of mounting nuts. Torque on the nonpressure plate mounting nuts should be 1 10 ft/lbs.
4. Check cotter pins to ensure they are in place.
5. Check all hoses and lines. They should be secure and
in good condition with sufficient length to allow for axle
movement.
Every 3,600 operating hours, 100,000 miles or one (1) year:
1. Disassemble and clean all parts. Clean all metal parts
in cleaning solvent, removing all rust and scale. Carefully
inspect all metal parts for cracks, distortion or damage.
All diaphragm sealing surfaces should be smooth and
clean.
2. Install new diaphragm or any other parts if they are worn
or deteriorated. Perform steps outlined in "Replacing the
Service Diaphragm". When the diaphragm, spring, or
both are replaced, they should be replaced in the
corresponding chamber on the same axle.
WARNING!
A piggyback spring brake chamber cannot have the
emergency diaphragm replaced. Replace the whole
piggyback spring brake chamber.
OPERATION & LEAKAGE TESTS
OPERATING TEST
1. Apply brakes and observe that the push rods move out
promptly and without binding.
2. Release brakes and observe that the push rods return to
the released position promptly and without binding.
3. Check push rod travel. Push rod travel should be as
short as possible without brakes dragging. Adjust travel
of push rod at slack adjuster if necessary .
LEAKAGE TEST
1. Make and hold a full brake application.
2. Using soap solution, coat clamping ring(s). If leakage is
detected, tighten clamping ring only enough to stop
leakage. DO NOT OVERTIGHTEN as this can distort
the sealing surface or clamping ring. Coat area around
push rod hole (loosen boot if necessary). No leakage is
permitted. If leakage is detected, the diaphragm must
be replaced.
2
SERVICE
PORT
SERVICE
PUSH ROD
LOCKNUT
COTTER PIN
FIGURE 2 - PIGGYBACK SPRING BRAKE DIAGRAM
EMERGENCY
PORT
MOUNTING
NUT
YOKE
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 an AD-IS
air dryer system or a dryer reservoir module, be
sure to drain the purge reservoir.
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