Fleet Maintenance - 24

ADBs take the linear force from the chamber
to an adjustment mechanism to help maintain
running clearance. A piston forced against the
backing plate of the friction pads applies pressure to both sides of the rotor, which is spinning
between the pads. This clamping process produces
the torque to help slow the vehicle.
These mechanical differences are the reason
for performance differences. One performance
aspect to consider is brake fade. Brake fade can
occur when the heat, built from the application
of friction, causes functional variations to the
braking system. With drum brakes, as the drum
surface heats up it expands away from the friction. This expansion increases running clearance
and, in turn, increases stopping distance. With
ADBs, as the rotor surface heats up it expands
toward the friction. This expansion decreases
running clearance and, in turn, decreases stopping distance.
"Operationally, ADBs have the ability to greatly
resist brake fade and provide a more consistent
brake torque application during almost all braking
situations," says Tony Ryan, technical services and
training manager for SAF-Holland. SAF-Holland

» Inspections on integral ADB components, such as brake pads and
calipers, can impact the system's service life and performance.
Photo courtesy of Bendix Spicer Foundation Brake

» The Hendrickson MAXX22T
air disc brake system
addresses the industry's
demand for an advanced
trailer air brake system, and also
offers significant weight savings.
Photo courtesy of Hendrickson Trailer Commercial Vehicle Systems

VehicleServicePros.com/10123676

24 Fleet Maintenance | August 2019

is a manufacturer and supplier of chassis-related systems and components
for trailers, trucks, and buses, as well
as a provider of wheel systems, brakes,
and axles.
"[ADBs] reduce stopping distance,
most notably at higher speeds," says
Keith McComsey, director of marketing and customer solutions, wheel end,
Bendix Spicer Foundation Brake. Bendix
Spicer Foundation Brake combines the
wheel end foundation brake technologies of Bendix Commercial Vehicle
Systems and Dana Commercial Vehicle
Products. The joint venture is a single
source for OEM brake system design,
manufacturing, hardware, and support
for foundation brake components and
actuation systems.
"[ADBs] virtually eliminate brake fade
... [which] is a variable the driver sees;
with a cold brake, the vehicle stops at
one distance, and when the brake gets
hot, that distance is extended. That variation to the driver is unpredictable. With
ADBs, it is much more consistent and can
be relied on by a driver," McComsey says.
Another performance advantage of
ADBs over drum brakes is the service
life of friction material. ADB pad changes are less frequent due to their efficient
on-road performance.
"With regard to tractor operation,
the feedback I'm getting from customers, whether with ADBs on steer, or
steer and drive [axles], is that they are

getting 350,000
to 500,000 miles
out of the brakes," says Greg Cooper,
disc brake product manager, field product
specialist, Stemco - Brake Products Group.
"They are not seeing that kind of life out of
their shoes. It is a significant difference."
Stemco is a manufacturer and supplier of
commercial vehicle systems and components, including wheel end components,
brake products, suspension products, and
tire and mileage solutions.
"On the trailer side, it varies - depending on how much use [the brakes] are
getting," Cooper says. "If the tractor is
equipped with drum brakes and the trailer is equipped with disc brakes, the trailer
pads will wear out faster than normal.
[ADBs] are a more responsive system, it
works a little harder and tends to stop
quicker; if it's pulling the tractor, they
may wear out quicker than anticipated."
ADBs can also reduce the potential for
Compliance, Safety, Accountability (CSA)
violations. When it comes to CSA violations mandated by the Federal Motor
Carrier Safety Administration, a large
portion are due to brakes that are out of
adjustment. A common cause leading to
brakes being out of proper adjustment
is rust jacking, or the buildup of rust
between the brake shoe and lining. ADBs
are less susceptible to rust jacking due
to their ability to keep contaminants out
from underneath friction material.

http://www.eberspaecher-na.com http://www.VehicleServicePros.com/10123676

Fleet Maintenance

Table of Contents for the Digital Edition of Fleet Maintenance