The most important tool in the box.
Talking Tools: Torque Wrenches
By: John Bellah
Torque 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.
We 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.
And 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. Always.
It 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.
There 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.
More 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.
When 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.
Also 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.
Being 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 ????.
Is 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 each pass.
John Bellah is Technical Editor for Police Fleet Manager Magazine and is a member of SAE International. He may be reached at firstname.lastname@example.org.