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Newbie, starting to work on my own cars, and I'd like to use air tools to save wear and tear on my wrists and arm muscles, and not aggravate back pain from a car accident years ago.

There are many discussions about making sure not to over-tighten bolts with air tools. I understand I need to restrict the pressure given to the air tools, and perhaps even use torque bars/sticks with an impact driver at least in the higher ranges they usually come in like 65-150 ft-lbs.

There are also many discussions about the risks of air tools breaking a bolt that's rusted on.

My question is if using torque bars/sticks with an impact driver when removing a rusty bolt would be a good idea. Assuming they work in reverse, anyway, which I'm hoping they can either for this purpose or left handed bolts.

My hope is to let the impact driver hit the bolt with a high but limited amount of force, and if that doesn't work, then try a torch or penetrating oil. Basically, to avoid torching or oiling when it's not necessary.

A couple of YouTube videos (Part 1 & Part 2) comparing various things like a torch, penetrating oil, CRC, acetone/ATF homebrew, etc, showed at least in those tests that the maximum needed without anything applied was about 132ft-lbs. (Although, an article shows way more, 516ft-lbs.) I'm hoping limiting the impact driver to 150ft-lbs might let it give it a shot, and cut down most of the risk of breaking it. I'm not seeing torque bars/sticks anywhere over 150 ft-lbs.

I guess it would be worth knowing the lowest torque that most rusted bolts break at, basically a "safe zone", but I haven't had luck finding someone looking at that.

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  • There are torque wrenches that go way over 150 ft-lbs, and some are 6ft long and heavy - used them on trucks so they exist.
    – Solar Mike
    Nov 12, 2019 at 5:51
  • @SolarMike - torque wrenches for sure. I'm talking about torque bars/sticks though. See floorjackshop.com/torque-sticks-what-are-they-and-do-i-need-one --- They are extensions which can be used with an impact driver, which flex at a set torque amount, preventing torque higher than the torque bar is rated from being placed on the bolt/fastener.
    – user1902689
    Nov 12, 2019 at 8:34
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    I remember seeing my father and uncle using a six foot breaker bar to get the rear axle nuts off an old VW beetle.It was a big nut, as I recall. If it were me, I'd start with penetrating oil and try a breaker bar or impact wrench. if that doesn't work try some heat.
    – Tim Nevins
    Nov 12, 2019 at 19:09

2 Answers 2

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The breaking point would be dependent on the size of the bolt, then significantly reduced due to the corrosion.

I think there's a higher chance of snapping the bolt with a breaker bar anyway, compared to an impact driver as the driver only applies rotating force to the nut.

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For larger fasteners, a bigger issue, when working on a rusty vehicle especially, is rounding the bolt heads/nuts with an impact gun. For smaller fasteners, breaking the bolt is probably more likely.

If you are concerned with either scenario, break the fasteners loose with hand tools (either a small ratchet or a breaker bar, depending on the fastener) so that you control the force input as much as possible. When using the breaker bar, take care to apply the force strictly straight or strictly perpendicularly, i.e. not at an angle, to avoid the tool jumping off of fastener or moving quickly in unexpected directions, possibly injuring the operator.

Once fasteners are disassembled, especially on a car that is driven in rain/snow, applying anti-seize to threads will go a long way toward making the next disassembly easy.

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  • Would anti-seize make a fastener act as if it were fastened to a lower torque? I've only used it on brakes (again, newbie.) Makes me wonder if it would make the fastener more "slippery", if you know what I mean. Like, if it was supposed to be fastened to 100ft-lbs, if it would come loose as if it were fastened to only 50ft-lbs or 75.
    – user1902689
    Nov 23, 2019 at 11:17
  • The effect is actually opposite - see blog.fcpeuro.com/6-tips-for-effective-use-of-anti-seize.
    – D. SM
    Nov 23, 2019 at 16:41

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