Professional_Tool_And_Equipment_News_December_2019 - 32

p The use of a dial indicator to check run-out can prevent come-backs.

expand when pressure is applied, reducing the pressure to the caliper. This is typically caused by using vice grips to prevent brake fluid leaking while removing
a caliper.
Damage may also occur when a technician allows the caliper to hang from
the vehicle by only the hose. Using wire,
wire ties, or a strap to hold the caliper
will not allow the hose to stretch, thereby
preventing damage.
Speaking of preventable errors, it's
best to open the bleeder screw prior to
collapsing the caliper when replacing
pads. Failure to open the bleeder will
allow dirty fluid to return to the master cylinder reservoir or ABS module
where it can contaminate the entire
system. Opening the bleeder screw will
allow fluid to escape rather than return
throughout the system.
In order to test for faulty hoses, master cylinders, restrictions in brake lines,
or faulty proportioning valves, the best
tool to use is a brake pressure gauge set
such as the OTC 7488A. Using a pressure
tester will provide you with an accurate
measurement of the fluid pressure that is
available at each point in the brake system, allowing you to determine where
an issue lies.
Another issue that frequently comes
up in brake servicing is broken, stripped,
or plugged bleeder screws. Removal of
a broken screw can be challenging, but

PTEN

DECEMBER 2019

there are quite a few tools on the market
that work, including just using a hack
saw to cut the top off of the bleeder, then
using a high-quality screw extractor to
remove the rest of the bleeder screw.
I have also seen instances where a
technician, trying to save a few minutes,
will only replace the copper washer on
the caliper side when installing a new
caliper. This practice can lead to a high
likelihood of fluid leaking at the caliper.

CASE STUDY:
UNCOMMON ISSUE

We recently had a 2007 Rav4 come to us
after its brake work was done at another
shop. The customer said they had the
front brakes replaced and a master cylinder and booster replaced about three
months earlier at this other shop. She
returned to them complaining of a harder pedal when she was stopping.
The initial shop rechecked the car,
then returned it to her after finding
nothing wrong. She took it back again
complaining about the same issue, and
this shop returned it to her saying they
bled the brakes, but still did not find
any issues.
The customer had the vehicle towed
in to our shop after she needed to make a
panic stop with extreme pedal effort (the
brake, ABS, and traction control warning
lights all came on). Thankfully she was
able to avoid a collision, but feeling it was

www.VehicleServicePros.com

p Note in this image the arm is bent, which
prevented the brake pedal pressure sensor
from sensing changes.

unsafe she had the car towed in.
We performed a visual inspection,
checked for codes and TSBs, and found
nothing. When we drove the vehicle, we
also did not feel anything abnormal during normal driving. When we did a hard
stop requiring an ABS activation though,
we did notice it took substantial effort to
push the pedal down.
We looked closely at the other repairs
that had been done to this vehicle and
found that the other shop had bent the
brake pedal position sensor when they
installed the brake booster. The switch,
as seen in the image, was bent to the
side and was not able to send a signal to the ABS system when the pedal
was depressed.
We looked up the system diagram and
operation in Mitchell 1 and found that
the system uses a brake pedal position
sensor as part of the Electronic Brake
Force Distribution (EBD) function of the
ABS system. We replaced the switch and
bracket, which is only serviced as part
of the complete pedal assembly. After
replacing the part, we drove the vehicle
and noticed a very slight change in the
pedal feel during normal braking, but
a significant difference during a hard
stop. We then returned the vehicle to the
customer, who stated the brakes finally
felt normal.

http://www.VehicleServicePros.com

Professional_Tool_And_Equipment_News_December_2019

Table of Contents for the Digital Edition of Professional_Tool_And_Equipment_News_December_2019