Air Impact Wrench


The best use of an air impact wrench is to remove wheel lug nuts. Do not use an impact wrench to tighten wheel lug nuts. The objective of this procedure is to show you how to correctly use an air impact wrench.

Part 1. Preparation and safety


  • Demonstrate the correct operation of an air impact wrench.

Using an air impact wrench

Personal safety

Whenever you perform a task in the workshop you must use personal protective clothing and equipment that is appropriate for the task and which conforms to your local safety regulations and policies. Among other items, this may include:

  • Work clothing - such as coveralls and steel-capped footwear
  • Eye protection - such as safety glasses and face masks
  • Ear protection - such as earmuffs and earplugs
  • Hand protection - such as rubber gloves and barrier cream
  • Respiratory equipment - such as face masks and valved respirators

If you are not certain what is appropriate or required, ask your supervisor.

Safety check

  • Make sure you direct the air exhaust of air tools away from yourself and others working in the area.
  • Always wear eye protection when using air tools.
  • Air tools generally produce more noise than electric tools, so wear ear protection when using air tools.
  • Make sure that you understand and observe all legislative and personal safety procedures when carrying out the following tasks. If you are unsure of what these are, ask your supervisor.

Points to note

  • The amount of torque an air impact wrench can produce will be determined by the pressure in the air system feeding it. Because this pressure will vary, there is no way of determining how much torque an impact wrench is applying to a fastener, so it is easy to over- or under-tighten fasteners.
  • The best use of an air impact wrench is to remove wheel lug nuts. Do not use an impact wrench to tighten wheel lug nuts.
  • Every impact wrench will have a control mechanism, so that it can be driven in either direction.
  • Always use six-point impact sockets when using an air impact wrench. Impact sockets are manufactured from a different blend of materials and have thicker walls than a standard socket.
  • Air tools are attached to the air supply by fittings that allow the supply to be connected and disconnected easily. Over time, these connections wear and produce an air leak. If the air leak is excessive, the output of the air tool will be reduced.
  • Air tools require lubrication. Most workshops have an automatic oiler incorporated in the air supply system. If your workshop does not have an automatic oiler, you will need to lubricate the air tools daily. Apply a few drops of oil to the inlet of the air tool before you use it.
  • An air impact wrench should be used to take up the looseness in a nut or stud. The final tightening must be undertaken by using a torque wrench set to the manufacturer's specifications.

Part 2: Step-by-step instruction

  1. Choose the correct tool
    Use the impact wrench, sometimes called the “rattle gun”, to loosen and remove the lug nuts on the wheels. The power and the vibration will loosen a tight nut, because of the torque produced by the wrench.
  2. Adjust the direction of operation
    Adjust the direction of spin: forward or backward with the wrench lever.
  3. Adjust the amount of torque
    Turn the valve to increase or reduce the torque.
  4. Correctly remove fasteners
    Never fully tighten the wheel nuts. If you over tighten them, the bolts may fail and cause the wheel to shear off the vehicle while it is moving. Always finish the job with a lug nut wrench.
  5. Use special sockets
    Make sure only to use the special impact sockets, extensions and joints. These sockets are special 6-point types and can withstand the sudden force that the impact wrench produces.
Tony Ferguson,
Feb 27, 2013, 7:53 AM