BENDIX BW7532 User Manual
2
Protecting the Spring
With broken power springs representing the leading cause of spring brake
malfunction,
malfunction,
it only makes sense to protect the spring at all costs. This may be
easier said than done.
A typical T30/30 spring brake is open to the environment via holes found on the
park-side housing. These openings serve as entry points for contamination such as
dirt, water, and de-icing chemicals. These corrosive contaminants can threaten the
power spring. A damaged spring may cause a leak if the diaphragm gets
punctured, or it may affect the stroke of the pushrod. Regardless of the damage,
the failed unit will need to be replaced immediately.
Because of corrosion concerns, most spring brake suppliers coat the springs to
provide some level of protection. However, the durability of such coatings is
compromised in lower-cost designs, which tend to compress the spring such that
the coils come in contact with one another. This type of design results in “coil clash,” which can wear away the
protective coating. Once the coating is worn, the bare spring is susceptible to corrosion, which can lead to
breakage.
The best protection against premature spring coating wear is to avoid coil clash. If the coils don’t rub together, the
coating will last longer. That’s the solution Bendix arrived at for its Bendix
A typical T30/30 spring brake is open to the environment via holes found on the
park-side housing. These openings serve as entry points for contamination such as
dirt, water, and de-icing chemicals. These corrosive contaminants can threaten the
power spring. A damaged spring may cause a leak if the diaphragm gets
punctured, or it may affect the stroke of the pushrod. Regardless of the damage,
the failed unit will need to be replaced immediately.
Because of corrosion concerns, most spring brake suppliers coat the springs to
provide some level of protection. However, the durability of such coatings is
compromised in lower-cost designs, which tend to compress the spring such that
the coils come in contact with one another. This type of design results in “coil clash,” which can wear away the
protective coating. Once the coating is worn, the bare spring is susceptible to corrosion, which can lead to
breakage.
The best protection against premature spring coating wear is to avoid coil clash. If the coils don’t rub together, the
coating will last longer. That’s the solution Bendix arrived at for its Bendix
®
EverSure
®
Spring Brake with No Touch
Technology. The springs are designed to virtually eliminate coil clash, protecting the premium epoxy coating used
on all Bendix power springs. This results in a longer lasting product and translates into fewer repairs, less
downtime, and lower fleet operating costs.
Ensuring Parking Force Output
on all Bendix power springs. This results in a longer lasting product and translates into fewer repairs, less
downtime, and lower fleet operating costs.
Ensuring Parking Force Output
A secondary issue caused by over-compressing the spring is a rapid decrease in force output. This reduces any
safety margin when parking a vehicle.
safety margin when parking a vehicle.
When evaluating spring brakes, a force output test can be used to measure the amount of
force the spring brake can produce throughout its stroke. This force output is measured
against SAE International’s recommendations. Having a high force output right out of the
box is important, but equally important is a spring’s ability to maintain high force output over
time, as all springs will degrade due to repeated compressions. This loss of force over time
is called sag loss.
Testing the force output of a spring brake out of the box and then after holding the spring in
the compressed position for specific periods of time will provide an indicator of how much
force output may be lost. Low-cost/low-quality spring brakes typically show low levels of
force out of the box, sometimes just meeting or even falling below SAE’s recommended
minimums. Even worse, these units show greatly diminished force output capability after
being compressed.
The increased height of the compressed spring in the Bendix
®
EverSure
®
Spring Brake
design reduces stresses on the spring, allowing it to better maintain force output over time.
This means drivers can park their vehicles with the same level of confidence for every stop.
This means drivers can park their vehicles with the same level of confidence for every stop.
Protecting the Center Seal
In addition to the power spring, another important feature on a spring brake is the center seal. This seal separates
the service and parking chambers of the unit and serves two important roles:
the service and parking chambers of the unit and serves two important roles:
1. Preventing leakage from one side of the unit to the other
2. Acting as a bearing that helps to guide the spring brake’s pushrod
2. Acting as a bearing that helps to guide the spring brake’s pushrod
A robust and smart design of the center seal components is therefore necessary to reduce any issues resulting
from damage or premature wear. Operating a spring brake places a large amount of force on the pushrod, some of
which may be lost due to friction. An improperly guided pushrod could significantly diminish the force output
delivered by the spring brake (due to high friction losses) and could also wear the seal or diaphragm prematurely,
typically resulting in a leak.
For new vehicles, OEMs must
certify that their braking
systems meet Federal Motor
Vehicle Safety Standard
(FMVSS) 121 parking
requirements.
No such standards exist for
aftermarket products, leaving
the parking force of low-quality
spring brakes to chance.
certify that their braking
systems meet Federal Motor
Vehicle Safety Standard
(FMVSS) 121 parking
requirements.
No such standards exist for
aftermarket products, leaving
the parking force of low-quality
spring brakes to chance.
The increased
height of the
compressed
spring in the
Bendix
height of the
compressed
spring in the
Bendix
®
EverSure
®
Spring Brake
design reduces
stresses on the
spring, allowing it
to better maintain
force output over
time. This means
drivers can park
their vehicles with
the same level of
confidence for
every stop.
design reduces
stresses on the
spring, allowing it
to better maintain
force output over
time. This means
drivers can park
their vehicles with
the same level of
confidence for
every stop.