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When I was in college I worked as a mechanic. It was a hard job, especially for someone like me. As a young woman with a leaner build, I didn't have much weight to throw at tasks that required lots of force. Often I'd find myself fashioning cheater bars out of an old bicycle frame or axle housing, then invoking some curse words like a witch casting a spell. It was inelegant, time-consuming, and exhausting over a nine-hour day. Power tools helped me a lot, and my best friend quickly became the impact wrench. Impact wrenches work by generating percussive force and converting it to a rotational force stronger than most people could manage with hand tools.
I have never owned a car newer than 25 years old, which means I have battled countless nuts and bolts frozen by rust, age, or physical damage. Maintaining a classic car is fun and rewarding but can be a constant challenge; an impact wrench makes certain tasks much easier. You don't need one for most jobs since most of the fasteners on your car aren't locked down that tightly. But for someone with physical limitations due to body type or injury, an impact wrench can be an essential tool.
Impact wrenches also allow mechanics to quickly remove a series of fasteners like wheel lugs or cylinder head bolts. Saving a few seconds on a task might not seem important, but those seconds add up quickly in a busy professional shop. Faster disassembly means more jobs completed each hour and more money for the shop and its technicians.
Different types of impact wrenches
Harbor Freight
There are a few types of impact wrenches, although most consumer-grade ones are battery-powered or pneumatic. Cordless units will be heavier in your hand because of their battery packs, although not wrestling with an air compressor and hose is a nice bonus when you're working alone or in a tight space. You'll get more torque from a good pneumatic impact wrench, although most battery-powered models are powerful enough for amateur mechanics working on passenger cars. Hydraulic impact wrenches are used for some heavy-duty industrial applications, and manual impact wrenches like the Craftsman CMMT14404 get their percussive force from hammer blows.
Regardless of what kind of impact wrench you use it will reduce hand and arm fatigue, in turn lessening the chance of mistake or injury. Impact wrenches meant fewer aching muscles for me as a professional mechanic and helps me the same way as a hobbyist. Impact wrenches have many applications when working on a car, but you'll still want to rely on hand tools for reassembly. Valve cover and suspension bolts in particular need to be torqued down precisely and evenly, so you'll want to learn about torque wrenches and get one for your toolbox. Tightening fasteners with an impact wrench could lead to stripped threads, broken studs and bolts, or other damage. You can buy a torque limiting extension bar set for your impact wrench, but it's always going to be safer tightening nuts and bolts by hand.
How impact wrenches save time
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Mechanics value impact wrenches for the time they save, but these tools do more than quickly zip out lug nuts. For example, constant velocity (CV) axle nuts are fastened with high torque and can only be removed if the wheel is prevented from turning. An impact wrench can remove most axle nuts off in seconds, saving the time needed to brace the wheel. Professional shops usually employ pneumatic impact wrenches, often connected to a permanently installed compressor. They're better for continuous use than cordless ones, which require charging and can overheat.
For professional mechanics one pesky bolt can mean hours of extra work and a disappointed customer, and impact wrenches eventually pay for themselves in busy shops. For an amateur, an impact wrench could be the difference between finishing a job at home or calling in an expensive professional. Fortunately there are a few affordable impact wrenches that owners love and are powerful enough for most automotive jobs. A good impact wrench can save you time, energy, and a few busted knuckles, but you might want to keep those breaker bars and extension pipes around just in case.
