Written by John Bellah
wrenches are one of the most important tools in the technician’s toolbox. In
days past, cast-iron, steel and aluminum were the normal materials that made up
automotive components. Back in those days a mechanic could do most assembly
operations by feel. Today we see far more exotic materials, tighter tolerances,
and closer torque specs. These exotic materials make the use of the torque
wrench even more important.
are all familiar with mechanics who can’t be bothered to look up frivolous
things like torque specs. They tighten everything by feel, either by
hand-tightening or by the “feel” of the impact wrench. Then there are the techs
who tighten fasteners to specification but then add a little “extra” just to be
sure. Of course, fasteners that are not sufficiently tight will eventually come
undone and ones that are tightened too much may strip or break.
then there is the tech at the tire shop who mounts the wheel on the hub and ties
the first nut down “really tight, dude,” with an impact wrench. He does the
same with the rest of the nuts, tightening in a circular pattern. When the
vehicle comes back with the complaint of brake pedal pulsation, the damage is
already done—from stripped lug-nuts and broken studs to warped rotors. Rotors
never warp like a potato chip from heat—they always “warp” from uneven wear.
is important to follow the manufacturer’s guidelines on whether the fastener is
to be lubricated, dry, or anti-seizing compound is applied during assembly, how
many stages is the object to be torqued, and in what sequence.
are numerous types of torque wrenches on the market today, and the experienced
technician probably owns more than one type of torque wrench. The simplest and
least expensive torque wrench is the “beam” type of wrench, where the socket is
mounted on a flexible beam, with a handle on the other end, which is coupled to
a pointer, indicating the amount of torque on a scale. These are readily
available in 1/4-inch, 3/8-inch, and 1/2-inch drives and are calibrated in
inch-pounds, foot-pounds, or the Metric equivalents.
exotic are the “clicker” torque wrenches, where the desired torque
specification is dialed in to a pre-set figure. These wrenches also have a
ratchet built in to them, whereas the beam wrenches don’t. When the desired
amount of torque is attained, the wrench will click and there is momentary
slippage at that point.
that amount of torque is exceeded, the wrench will continue to exert twisting
force until the operator reduces pressure. There are different variations of
these wrenches and some may have a dial indicator. Also available are digital
torque-wrenches, which have a digital read-out you can pre-set. The downside on
the digital torque wrench is it requires a battery.
available are torque-limiting ratchets and ¾-inch and 1-inch torque extensions,
which are designed for mounting truck tires. The torque extensions will limit
torque to between 150 and 550 pounds, depending on the application.
precision instruments, torque wrenches require a certain amount of care to
maintain their accuracy. They don’t like to be dropped, and the manufacturers
recommend storing the click and digital wrenches in the plastic case they were
shipped in to prevent damage. When not in use, it is suggested they be set to
the lowest figure possible to keep the internal springs from stretching or
retaining a “set.” Periodic oiling is also recommended—follow the
manufacturer’s guidelines. It is also suggested that calibration is checked
periodically along with ????.
one torque wrench better than another? As long as they are accurate, all should
work equally as well; however, if one is working on a complex project with
various different torque readings, the old-fashioned “beam” wrench may be the
more versatile tool, rather than having to re-set the several times unit during
John Bellah is Technical Editor for Police Fleet
Manager Magazine and is a member of SAE
International. He may be reached at email@example.com.
Published in Police Fleet Manager, May/Jun 2014
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