Technicians receive a lot of training to ensure that truck wheels are properly attached, but myths about tools and installation procedures still have a way of getting around. (Isn't an impact gun good...
Technicians receive a lot of training to ensure that truck wheels are properly attached, but myths about tools and installation procedures still have a way of getting around. (Isn’t an impact gun good enough? Does the star pattern really make a difference? This is going to take forever!)
A panel of experts recently challenged these misconceptions with real-world tests, and their findings may surprise you.
Myth 1 –
A torque wrench is a magic wand that guarantees torque
Calibrated torque wrenches are valuable tools, but they still require an attention to detail. Look no further than the simple mistakes that can be made when measuring readings, particularly on tools that include a combination of metric and imperial scales.
“A Newton-meter and foot-pound differ markedly,” notes Greg Katsis of Tenexes Tensioning Systems.
But the mistakes are not limited to reading the wrong side of a scale. A technician who holds the tool in the wrong spot will also apply an inconsistent amount of torque.
“As the hand moves, the output changes markedly,” Katsis said, referring to a video that demonstrated different hand positions. As the installer moved his hand away from the proper position -a spot that is clearly identified on the handle -there was a 10% shift in the resulting force.
It was even possible to apply extra torque when using a break back wrench design. “It cammed over and kept going,” he noted.
Myth 2 –
Using proper torque techniques takes too much time
Any technician with an impact wrench in their hands will tend to argue that proper fastening techniques take too much time.
In reality, the difference between the use of a torque wrench and impact gun can be measured in seconds, said Bandag’s Randy Patterson, after fastening a wheel in place using a variety of tools. Work with the 3/4- inch impact gun took 30 seconds, the pneumatic torque wrench accomplished the job in 83 seconds, and the manual break back torque wrench required 110 seconds of time.
“It’s a little bit slower, but it’s not a lot slower,” he said.
Myth 3 –
Re-torquing is always necessary
Installation manuals tend to insist on the re-torquing of newly installed wheels within 160 km, but members of the panel questioned whether that step should always be required.
Instead of re-torquing every wheel, Alcoa’s Dave Walters suggested that fleets should simply be able to install 30 wheel-ends, re-measure the torque of the related fasteners after 160 km, and then record the details. That should be enough to prove that a fleet is following proper installation procedures, he said.
Ultimately, the point was made because proper installation procedures will hold the fasteners in place for many kilometres to come. These proper steps include using a wire brush to clean studs, mounting faces, hub pilot pads and hub bores -particularly at a time when new de-icing compounds are corroding parts faster than ever. And while he recommends a couple of drops of 30-weight oil for the flange, washers and threads before tightening a fastener, he shies away from anti-seize compounds because of a lack of consistency between the different brands and types.
Still, one Canadian member of the audience questioned whether a fleet can afford to ignore the re-torquing procedures. After all, Ontario could fine a fleet as much as $50,000 for a lost truck wheel, and the average fines for such losses have still been around $3,000.
It could be an expensive gamble.
Myth 4 –
Star patterns are a must
Kevin Rohlwing of the Tire Industry Association says that a secret to the consistent tightening of wheel fasteners involves using a star pattern during installation procedures. And that’s true -in most cases.
Using an air gun in one trip around the wheel, he found fastener torques that ranged between 2.4 and 431 lb-ft. And the “snug and bump” method didn’t fare much better. Even after the air gun made two complete trips around the wheel, the final “bump” still left fasteners with torques ranging from 340 to 455 lb-ft.
When he switched to a star pattern -working back and forth across the face of the wheel -his air gun ensured that each fastener offered a torque between 337 and 502 lb-ft. The different approach helped to ensure that the wheel was properly seated in place. And when he used a torque wrench in this pattern, the fasteners were tightened to torques ranging between 471 and 588 lb-ft. (The highest torques were blamed on aging fasteners.)
The biggest surprise, however, was that the torque wrench still offered sound results when working clockwise around the wheel. The fasteners were ultimately tightened to torques ranging between 451 and 602 lb-ft.
This showed that the use of a torque wrench is still the most important consideration.
Myth 5 –
Big wheels require big air guns
Some shops may use one-inch impact guns to loosen stuck fasteners, but a 3/4-inch impact gun is usually more than enough, says Rohlwing, noting how North American shops are the only ones to use such tools when installing wheels.
“There’s so much more power [delivering 1,400 lb-ft of force compared to the 1,100 lb-ft of a 3/4-inch tool] that, if you hit on the nut to hard, it will go over.”
Myth 6 –
Torque sticks are needed to confirm torque levels
“Maybe in automotive they’ll work,”Walters says of torque sticks,”but we didn’t get any consistent results.”
Ultimately, the torque sticks are only as effective as the impact wrench to which they’re attached, adds Rohlwing. If the tool’s supply of air is interrupted, the torque stick will still deliver too little torque.