The basic aim with this “Tools You Should Own” series is to help you out in your own garage. We all hit that point when, for lack of a certain tool, or lack of knowledge about a certain tool, we hit a wall and can’t progress with a repair. That feeling sucks, so let’s not do it.
What Are They?
Impact drivers are exactly what they say on the tin. They don’t just turn (driver) but they whack (impact). Some are manual, and some are powered. The powered ones come in pneumatic and electric flavors.
I can’t say that any type of impact driver is “better” than any other, but they do each have their place in your toolbox.
Generally when we go about removing fasteners we start with a simple driver, or a bit on a ratcheting socket wrench, blithe and naive, applying pressure… and more pressure… and then the tool twists. Or the fastener head begins to round out, the tool breaks, or you run out of grunt.
At that point, you’ll need to call on your experience: Does this fastener need a Bigger Lever? Or will more leverage break the fastener, or round out the mating surface?
Before the fastener head shears flush with the surface of the part you’re trying to remove, take stock. Think about how many heat cycles everything has been through, how rusty everything looks, how the fastener looks like a different metal than the part and so perhaps we’re dealing with galvanic corrosion.
This is when an impact driver might just shine. They do not spin much, but they spin a little bit very hard, and that’s the key to their usefulness.
Manual (Hand) Impact Driver
A manual impact driver is good for fasteners that are well-seated in a large, heavy metal object. I have used them to good effect on things like exhaust header bolts and intake bolts under carburetors (the ones that hold the intake pipes to the engine block). Sometimes they take several whacks and sometimes you need something along the lines of a handheld (or larger) sledge to get the most out of them. They are satisfying to use and rather effective: when you strike the blunt end with a hammer, the driver end twists. They are “safer” to use on fasteners that might be a bit fragile.
Electric and Pneumatic Impact Driver
It used to be that cordless electric impact guns were not very powerful and only moderately useful, but batteries and electric motors have come a long way since we first met them. These days, an electric impact gun can handle a lot of things that used to be the domain of the pneumatic. They are lighter weight and much, much more portable (we aren’t always at home or next to our compressor when we need an impact gun).
Electric and pneumatic impact guns both work the same way. They deliver impact force along with twisting force to break the grip of the fastener. I break out my pneumatic impact gun when I need to loosen axle bolts or countershaft sprocket nuts. You know, the big stuff.
When a breaker bar isn’t doing the trick and/or you’re worried about breaking the fastener, that is where an impact driver shines.
Hand impact drivers are not expensive. Electric impact guns are more expensive but can be had for under $100. Pneumatic guns are worth buying quality. You will also need an air compressor to drive them, and sockets rated for impact use, so they are not an insignificant investment. They’re worth it, though. The moment a stuck fastener comes loose under impact is the moment you’re pretty sure you can do magic.