Fleet Maintenance - 22

Furthermore, the applied pedal force is proportional to the braking force, thereby giving the
driver the ability to control the rate of vehicle
deceleration, Jendrusch says.
Hydraulic braking systems are specified on
Class 1 through 5 vehicles with a Gross Vehicle
Weight Rating (GVWR) of up to 19,500 lbs. Class 7
and 8 vehicles, with a GVWR of more than 26,000
lbs, are specified with air braking systems. Class
6 vehicles, within the 19,500- to 26,000-lb range,
may be specified with either hydraulic or air braking systems. However, hydraulic braking systems
are never specified on vehicles with a GVWR
greater than 26,000 lbs, as hydraulic brakes have
limitations to the amount of brake force that can
be generated, Jendrusch says.
"Cost, packaging, and ease of operation are
the most obvious benefits [of hydraulic brakes],"
Jendrusch continues.
Another benefit is that operating a medium duty
truck with a GVWR of no more than 26,000 lbs
does not require a Commercial Driver's License
(CDL) if the vehicle is specified with hydraulic
brakes, he adds.

»Phoenix Systems offers the BrakeStrip,
designed to test the level of copper within
brake fluid. The company recommends
changing the vehicle's brake fluid should the
test measure 200 parts per million of copper.
Photos courtesy of Phoenix Systems

Maintenance considerations

There are certain aspects of the hydraulic braking system that technicians should be mindful
of; such attentiveness will allow them to spot
warning signs of an impending failure and can
ultimately prevent unwanted downtime.
Jendrusch recommends technicians check that
nothing is touching or rubbing against the brake
tubes and hoses, as such contact could lead to
premature wear and failure of these components.
Unwanted contact could lead to wearing of corrosion protection which could cause tubing deterioration. Jendrusch further recommends that caliper
guide pins are properly lubricated. Proper lubrication will ensure that the caliper operates and slides
as designed, promoting even brake pad wear.
"Whenever the calipers are serviced, the lubrication of the guide pins should be checked to
ensure free movement of the caliper," Jendrusch
emphasizes.
»It is recommended fleets test the
copper levels of the brake fluid each time
the vehicle is in for an oil change.
132053578 | Vitpho | Dreamstime.com

22 Fleet Maintenance | October 2020

When service technicians inspect vehicles
coming into the shop, they should always check
the braking system, and specifically the brake
pads, advises Jeremiah Terry, general manager
of Phoenix Systems, a provider of tools and technology for the auto care industry.
"They might want to watch for any sort of
wobbling or shaking that might [indicate] a rotor
that's warped ... They want to look for any squeals
or loud sounds coming from the brake system,"
Terry suggests. "And then, last of all, specific to
hydraulic is, of course, the brake fluid."

Brake fluid is the lifeblood of the hydraulic
braking system. Its performance and status affects
the hydraulic braking system in its entirety, so
proper maintenance is of the utmost importance.
One visible warning sign drivers and technicians alike should watch for is the "low brake
fluid" indicator light on the vehicle dashboard,
typically represented as an exclamation point
within a parenthesized circle.
"Brake fluid wears out over time, but not from
just sitting," Terry says. "It takes driving. The
brakes get really hot when driving down a hill,
from stop-and-go driving, [et cetera]. That heat
is transferred into the brake fluid; the heat, plus
oxygen, seeps in through the rubber hoses as well
as through the cap and the master cylinder."
The combination of heat and oxygen in the
brake fluid begins to break down the fluid and
leads to corrosion inside of the braking system,
Terry warns. The first victim of the corrosion
process is the copper inside of the brake lining.
As the amount of copper increases in the brake
fluid, it starts "attacking" all the iron components
in the braking system.
"That is when people usually will get stuck calipers," he says. "They'll come in and their caliper
is stuck, it's pinched tight, or maybe the caliper is
not coming out. And so, the [vehicle] is pulling to
the right or the left. This is all caused by corrosion
taking place inside the brake system because the
brake fluid is worn out."
To avoid such corrosion, Terry recommends
utilizing Phoenix Systems' BrakeStrip or the
BrakeStrip Plus. The BrakeStrip is a test strip for
copper in the brake fluid; the strip can be dipped
in the brake fluid to determine the level of copper
within the fluid. Doing so reveals how much
corrosion is occurring in the braking system.
Terry notes that a vehicle's brake fluid should be
changed before the fluid measures at 200 parts
per million of copper.
Terry further recommends that fleets test the
copper levels of the brake fluid each time the vehicle is in for an oil change.
"In a fleet, if the vehicles are all being used for
the same type of operation, same type of driving,
then they'll start seeing a mileage correlation [as
to] when the brake fluid fails," he says. "That being
said, though, that [assumes] they all started with
the same brand of brake fluid, [as] every brand
is different."

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Fleet Maintenance

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