May_2021 - 42

TOOL BRIEFING
tial usage cases are near endless. Multiple
OEMs are including NVH testing into
their diagnostic routines to help isolate
failures of everything from misaligned
mounts to torque convertor shudder
and more.
NVH data can quickly allow technicians to differentiate between a wheel/
tire vibration, suspension or mount fault,
an out-of-balance driveshaft, or engine
harmonics. This data takes us further
from subjective analysis and puts the
symptoms into a format that is much
more objective, as well as being useful in
the future as a record of a " known good "
or " known bad " vehicle. This creates the
ability for a technician to back up their
" gut feeling " of shifted cords in a tire or
a failing wheel bearing with concrete
readings from previous failures on the
same or similar vehicles. The more data
we have, the more we can feel confident
in performing the proper repairs for
the customer.
The ability to document before and
after vibration measurements is just
another arrow in the target of a firsttime fix. These reports add another level
of value to the alignment and balancing
services that technicians are currently
providing. There are a few systems
out there, so research is key to making
a selection.

p Figure 3- The Pico Technology NVH Interface allows for capture of vibration in three
axes during a test drive.

STEP 3: INITIAL
ALIGNMENT CHECK OUT
Now we are ready to hit the alignment
rack and get our measurements (Figure
4). Proper installation of the alignment
heads (per the system's instructions) is a
critical first step here.
Once we've gathered our initial readings, it's time to take a second to examine
and analyze the data and see where it is
pointing us.
First off, there are the regular angles
we are all familiar with: camber, caster,
toe, and thrust angle. Thrust angle has
become even more important in recent
years due to the advent of ADAS and
many OEMs dictating that calibration
target set-up and measurements are

PTEN

MAY 2021

p Figure 4 - The Hunter Win-Align system.

based off of the center line of the vehicle.
Without a proper thrust angle, every
other angle and related system will not
function optimally.
Steering axis inclination (SAI) and
included angle are two additional angles,
often called diagnostic angles, that are
incredibly important when it comes to
analyzing and performing alignments.
SAI is a very important and often overlooked component of alignment diagnostics. SAI causes both front wheels to gain

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positive camber as they steer away from
the center line. When combined with the
proper specification caster angles, the
front wheels self-center and help generate straight line stability.
As the wheels turn to one side or the
other, the wheel is pushed up, which raises the front of the vehicle. The weight of
the vehicle is also pushing down on the
suspension so that when the steering
wheel is released the wheels, and steering wheel, return to center.

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May_2021

Table of Contents for the Digital Edition of May_2021