not so fast!
Wrongful Use of Impact Wrenches in Over-Tightening Wheel Nuts
Let’s Start a Campaign to Ban Mechanics and Tyre Fitters from using Air-Guns!
NOT SO FAST! Next time you have your tyres changed/brakes/discs/pads or pretty much anything that requires your wheels to be removed in the first place. Insist that your Mechanic or Tyre Fitter uses a ‘Torque Wrench’ to tighten the locking wheel nuts on your vehicle (please refer to your vehicle owner’s manual for the correct torque settings). Do not allow them to use an ‘Impact Wrench’.
Garages increasingly advertise that they don’t use impact wrenches as more drivers become aware that the locking wheel nuts can be overtightened as a result. This is more than an annoyance, when it comes to trying to remove a wheel with over-tightened wheel nuts. The sheer power of the impact wrench damages the locking wheel nut key and can also damage the locking wheel nuts. Instead, the locking wheel nuts need to be tightened by hand, using a calibrated ‘Torque Wrench’.
How Impact Wrenches Work
An impact wrench (also known as an impactor, impact spanner, impact gun, air wrench, air gun, rattle gun, torque gun, windy gun) is a socket wrench power tool designed to deliver high torque output with minimal exertion by the user, by storing energy in a rotating mass, then delivering it suddenly to the output shaft.
Impact wrenches look somewhat like electric drills, but other than looks, these two types of wrenches do not have much in common. While a drill supplies constant rotational power at a relatively high speed, an impact wrench is designed to provide high torque at a low speed.
Actually, the impact wrench does not provide constant torque. Instead, it is more akin to putting a wrench on the nut or bolt that needs to be loosened and hitting it with a hammer, turning it in small, incremental stages. As power is applied to the impact wrench, an internal "hammer" strikes against an anvil, which is connected to the square drive on the end of the wrench. This attempts to force the tool (usually a socket) that is attached to the air drive to turn.
The amount of force they apply to loosen tight fasteners is extensive. It is sufficient to cause locking wheel nut keys/fasteners and tools to break. The biggest disadvantage of impact wrenches is that it is hard to control the power on them. They do not have variable-speed triggers, nor is the amount of power they provide easily adjusted. These tools after-all are for breaking things loose or tightening them very tight! They do that well, but if a small amount of power is needed, such as for loosening a stubborn screw or removing locking wheel nuts, they will provide too much power, either breaking the screw head off or stripping out the locking wheel nut key or locking wheel nut.
The only time it is advisable to use an impact wrench is if the wheel nuts have been over-tightened and all other methods of removal with a torque wrench or similar have failed. Be careful not to apply the impact wrench obliquely as this can cause the locking wheel nut key to fracture and damage the locking wheel nut security pattern.