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I broke two of my car's lug nut studs, and I had to take the car to mechanic for repair. The mechanic explained that sometimes lug nuts are highly over-torqued because all shops use impact gun to tighten them, but does not cause any problems as long as they are opened using an impact wrench.

Also, my mechanic explained that using a breaker bar (like below) in over-torqued situations can damage the studs.

breaker bar

Is to correct to say that avoiding breaker bars and using an impact wrench instead prevents damage to nuts or bolts?

Is it correct to say that over-torquing lug nuts with an impact gun is fine as long as we open them with impact gun rather than a breaker bar?

Uodate 1:

I understand and completely agree that a torque wrench is the best approach. However, that is not the context of this question. So we should move from the ideal world to real world where most mechanic shops use impact gun. When we need to open to open an over-torqued lug nut, I can think of 3 options to handle the situation:

  • Option 1: use a breaker bar. Well that broke my lug stud :(
  • Option 2: Use an impact gun to open the lug nut. My mechanic claims that it always works for him without breaking the stud. He suggested that I should have used this option.
  • Option 3: use a lubricant such as W40. Many people don’t like the idea since it changes the torque spec of the lug nuts

The question is which of the above option should I consider or is there a better option?

Update 2

I 100% agree that a torque wrench should be used in the 1st place. However, when we end up with an over tighten nut, a breaker bar can cause more damage compare to a similar rotational force created by a four-way or torque gun. It was a mystery to me how come my mechanic never ended up breaking my lug studs, and I broke 4 of them at the 1st try!! He always uses a torque gun, and I used a breaker bar.

Once again, I 100% agree that a torque wrench should have been used in the 1st place. Can't emphasise it enough

It costed me $160 to earn this experience, I hope this post save someone else's lug studs :) It is possible to find a fine corded impact wrench for $40, which is fine for home use. I got this one: http://www.homedepot.ca/product/18-volt-one-1-2-in-cordless-3-speed-impact-wrench-tool-only/919361 here is a demo video: https://www.youtube.com/watch?v=CvvDYHZ-GeM

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    With a decent torque wrench only costing $20 from Harbor Freight (and yes, they are actually decent wrenches, given the price or not), to my mind there is no reason not to get one. Even if a shop does not use a torque wrench to put the lugs on doesn't mean you cannot come behind them and make things right. To me this negates you "real world" comment and moves us back to the ideal world. Besides, you don't use a torque wrench to take the lugs off. If you want to talk ideal/real world, it's a lot more affordable for the average person to own a torque wrench than an impact gun. – Pᴀᴜʟsᴛᴇʀ2 Nov 1 '15 at 20:23
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    If you loosen them right after they are put on, it is much easier than if you leave them there for a long time and then try to do it. You get a build up of any corrosion, plus space welding, and you've got stuck lugs. If you break them free and torque them properly in the first place, you can use whatever you like and they'll come off readily. It's a case of an ounce of prevention is worth a pound of cure type scenario. – Pᴀᴜʟsᴛᴇʀ2 Nov 1 '15 at 21:17
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    I am doing some experiment with my new impact gun. It seems that an impact gun does much better job handling an over-torqued nut. The continues force that a breaker bar imposes can easily destroy bolts or studs. Whereas, an impact gun can open nuts with no damage. There must be a mechanical explanation for this. Impact force must be different than continues force when it comes to opening a nut. – Allan Xu Nov 2 '15 at 1:00
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    @AllanXu, it's true that an impact wrench is different. You can also break bolts with them. Proof by existence: I've done it many times. They aren't magic. – Bob Cross Nov 2 '15 at 14:22
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    I agree with Paulster2. Id go further though and insist that the workshop torque the wheel nuts correctly. I don't accept their laziness as an excuse for damaging my car. If they can't or won't do it properly go somewhere else. – Sir Swears-a-lot Nov 3 '15 at 9:14
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I can see where your mechanic is coming from. The reason being that, although like Steve Cross notes, the impact wrench applies a lot of force suddenly, it applies the force in an evenly rotational direction. ANY wiggle in the socket (Which there will always be or you wouldn't be able to get it on the nut) and the breaker bar will be putting lateral force along with the rotational force. That will increase chances of breaking the stud. This is why steveverrill recommends to hold the nut end when using a breaker bar, although I'm not sure if that would do much good with so much leverage.

I don't have an impact wrench, and having broken a few studs using a bar or the tire tool that comes with the car, now I always use a four-way to remove lug nuts. It's not as good as an impact wrench but the upward force on one side helps balance the downward force on the other. I've never broken a stud with a four-way. (I have, though, broken a four-way, be careful.)

I was at a shop once and their impact wrench wouldn't budge the nut, so the mechanic said he couldn't change my tire. I asked him about a breaker bar. He said he had one but he couldn't use it because the shop would be liable for a broken stud - which is messed up because it was the same shop that put those nuts on in the first place. He told me if I wanted, I could back it out the door and do it myself, which I did successfully.

  • Thanks Tom.Your answer aligns with my experiment. A breaker bar should be avoided. There is a less chance ending up with a broken stud that with a strong rotational force such as a four-way or torque gun. Once again, I 100% agree that a torque wrench should have been used at the 1st place. – Allan Xu Nov 5 '15 at 23:17
  • BTW, sometimes retailers have nice specials on corded impact guns. Like this one for $40: youtube.com/watch?v=vIoH0gDtkjs. He is not using it correctly, though. – Allan Xu Nov 5 '15 at 23:26
  • That wouldn't be a bad idea. Thanks. As a side note, I have no idea what the torque specs are for my work van but once I had a tow truck guy change a flat. He used a neumatic impact wrench on the lug bolts. I drove it the whole next day then on the second day I had two lug bolts fall off and one break off. Since then any time a tire is off a vehicle our mechanic comes back the following day and re-tightens them with a three-foot long torque wrench. He has to grab the end and pull back with all his weight. I'm sure I don't have the strength to loosen them. – Tom Nov 5 '15 at 23:40
  • I bought this one and using it as a torque wrench: canadiantire.ca/en/tools-hardware/measuring-tools/… – Allan Xu Nov 5 '15 at 23:45
  • Sounds like a good reason for me to buy a impact wrench (for removal)! Thanks :) – Jason Capriotti Apr 2 '18 at 14:58
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tl;dr: No. An impact wrench isn't a cure-all.

The mechanic explained that sometimes lug nuts are much over torque because all shops use impact gun to tighten them. That does not cause any problem as long as they are opened using an impact wrench.

Well, that's not quite true. Over-torque is bad in and of itself. At a very high level, it damages the threads on the studs, puts strain on the stud itself and can cause warping of the rotor and wheel that it's attached to.

Is to correct to say that avoiding breaker bars and using an impact wrench instead prevent damaging though nuts or bolts?

Prevent? No. If your lug nuts were over-torqued, you already have a problem and some damage has been done. Admittedly, it might be relatively minor but torque specs exist for a reason.

However, when you have a stuck bolt (due to rust, over-torque or just general perversity of the universe), you sometimes need to explore other tools and techniques. For example, one trick I've used at the end of winter is to get the nuts off that I can, hit the remainder with some penetrating oil and then raise and lower the car on the jack a couple of times. The motion of the wheel as the load is added and taken away can sometimes unstick a nut.

Likewise, I frequently use an impact wrench to loosen nuts. If it's not working, I'll back off, though and try a different tool. This was a hard-learned lesson....

Is it correct to say that over torquing lug nuts with an impact gun is fine as long as we open them with impact gun rather than a beaker bar?

"Fine"? No. Is this a magic impact wrench that can be set to the proper torque spec? I doubt it. Remember that an impact wrench has "impact" in the name. It is hitting the fitting with impulsive torque rapidly. It doesn't do a soft landing when it starts approaching the correct torque spec.

Quoting Wikipedia:

An impact wrench (also known as an impactor, 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.

See that "suddenly"? It's not going to be able to stop itself on a dime.

There are plenty of motorized hand tools that do have coarse torque settings. I will often use those for the boring parts (going from zero to about 75% torque). Then I'll switch to the torque wrench for the exact specification.

  • +1 It can be quite a chore to get wheel nuts to budge, but once they do it's usually plain sailing thereafter. I cannot recommend using penetrating fluid/rust solvent enough to help in such circumstances. – Zaid Nov 1 '15 at 15:44
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    I cannot stress enough the need to use torque wrenches to apply the proper torque to the lug nuts. I will most often loosen and retinue the lugs after getting my vehicles home from the tire shop just because of what I see them do in their shops, whether they use a torque wrench or not (technicians often don't know how to correctly use a torque wrench even if the use one). – Pᴀᴜʟsᴛᴇʀ2 Nov 1 '15 at 16:45
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    I appreciate the elaborate answer and I learned from it. However, please consider that I am asking how to deal with an over torqued nut and your response says when I have an over torqued nut, I am doomed, and nothing can be done. This is almost a year after this post, and I am using impact wrench to open lug-nuts. No broken socket so far. I will be updating next year as well and maybe post a video. – Allan Xu Sep 28 '16 at 15:25
  • @AllanXu, I don't think I said that you're doomed. I did say that you might other problems besides the fact that the nut is too tight. I also use an impact wrench to loosen nuts. What I did say was that putting nuts on with an impact wrench is likely going to cause those problems. Warping the rotor isn't going to be fixed by using a different tool to remove the nut. – Bob Cross Sep 28 '16 at 15:49
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In my experience, garages always tighten wheelnuts so much that you have a major challenge getting them undone if you have a puncture. While they shouldn't do this, it obviously gets them in less trouble than it would if your wheel fell off, so they will continue to do it.

Using excessive force on a short bar will damage your wheel nuts. Force will not undo them. Torque does. A nice long bar like in your photo will apply more torque with less force. I would put my other hand on the nut though, to balance the force applied to the bar, and ensure as much as possible that only torque is applied to the wheel nut.

It's not realistic to carry an impact wrench in your car to fix a puncture. It's also not realistic to unscrew a wheel with the crappy spanner supplied in the car manufacturer's toolkit. They're normally so short they need to be jumped up and down on to have any hope of moving anything, which guarantees breakage of something (usually of the spanner.) So carry a nice long bar to be able to apply torque to your wheelnuts at the roadside when you have that puncture

Opinion is divided on whether it's a good idea to put a tube over the end of a bar to give more leverage. I say, if you haven't got anything better, it will do (it worked for me when I got a puncture 3 miles from the nearest tarmac road.) The worst that can happen is you break the fastener, but if it's not coming off you have little to lose (especially if you've had security wheelnuts fitted and have the old non-secure ones in your car.) Don't attempt it with a ratchet wrench though. The ratchet will be the first thing to go.

Conclusion: wheelnuts are invariably done up too tight. They shouldn't be but they are. Impact wrench should get them undone, but long bar is better than short bar.

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I have broken a few bolts using a bar and none using a impact gun. Sometimes my gun won't budge it and because the bar starts okay I carry on. The problem occurs when it first turns the bolt, then gets harder due to a cumulative build up of corrosion on the threads. I think the bar winds the bolt past it's elastic limit but the gun using multiple quick bursts allows the bolt to budge, reset and budge again. I know it's way more technical than that, but you have a lot of time to reflect seconds after the breaker bar goes uncomfortably soft to turn then falls away with the head of the bolt!

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