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Milwaukee M18 impact can't undo the bolts it tightened


lonewolf

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I just bought a Milwauke M18 impact wrench (model# 2763-22). Used it to torque down the lug bolts on a couple wheels on a VW Jetta this past weekend. Got carried away and overtightened them to at least 200 ft-lbs, when they should be tigthened to 90 ft-lbs. Tried to remove them with the M18 impact, and it won't take them off!! I'd hammer for a good 10 seconds, and nothing. The battery was at full charge and the impact seemed to be hammering at full force.

 

I had 6 bolts that were way too tight. 1 it eventually was able to remove. For the others I used my 3 foot long breaker bar. Removed 4. 1 got its head stripped and will need to be drilled out.

 

Now my question is how can it be that the impact cannot unbolt the same bolts it tightened just minutes ago? It is rated at 700 ft-lbs tightening torque, and 1100 ft-lbs nut busting torque. My 3 foot long breaker bar and my 190 lbs weight probably put no more than 300 ft-lbs of torque to undo the bolts. Is this normal, am I expecting too much from the M18 impact?

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Reason can be found in Newton's laws. It will always take more torque to break a nut than you tightened it, objects like to stay in motion. Breaking a nut is trying to move an object not in motion, which takes more force. It's not exactly intuitive when you're thinking about rotational force as opposed to moving in a straight line but the physics still stand up.

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Just now, BMack37 said:

Reason can be found in Newton's laws. It will always take more torque to break a nut than you tightened it, objects like to stay in motion. Breaking a nut is trying to move an object not in motion, which takes more force. It's not exactly intuitive when you're thinking about rotational force as opposed to moving in a straight line but the physics still stand up.

The thing is though all impact wrenches I have used are designed so that they make a good amount more torque in reverse than in forward. I have the impact in question and it has removed every bolt thrown at it but one. I would contact Milwaukee and see what they say. Something isn't right there.

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6 minutes ago, NicholasShetley said:

The thing is though all impact wrenches I have used are designed so that they make a good amount more torque in reverse than in forward. I have the impact in question and it has removed every bolt thrown at it but one. I would contact Milwaukee and see what they say. Something isn't right there.

 

It should but I've seen it on plenty of impacts where it doesn't. I think it can also go beyond the general physics and get into the materials involved. I've seen a lot of issues with alloy wheels and lug nuts being overtorqued. Alloys tend to seize...it's why I keep a dead blow hammer in my SUV.

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1 hour ago, BMack37 said:

Reason can be found in Newton's laws. It will always take more torque to break a nut than you tightened it, objects like to stay in motion. Breaking a nut is trying to move an object not in motion, which takes more force. It's not exactly intuitive when you're thinking about rotational force as opposed to moving in a straight line but the physics still stand up.

 

That's understandable. What I don't understand is how I was able to break the lug bolts with about 300 ft-lbs (by using a breaker bar) when the impact can output 1100 ft-lbs?!

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8 hours ago, 99_XC600 said:

That's odd. But as a general rule, I never use an impact to go to final torque. I've always used a torque wrench. 

This... You really shouldn't be torquing down your lugs like that. You risk the chance of weakening the studs and potentialy having them shear under load, also you can warp your wheels. I'd tighten them up to snug then hand toque them the last little bit.

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Isn't that impact a 2 speed? Do you have it in the right setting?  I thought I read it has a low torque setting at 100 ftlbs (for lug nuts I presume?) and a full power setting where you get the 700/1100.   Just a thought...

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4 hours ago, lonewolf said:

 

That's understandable. What I don't understand is how I was able to break the lug bolts with about 300 ft-lbs (by using a breaker bar) when the impact can output 1100 ft-lbs?!

 

My guess is leverage and constant applied force but I'm not a physicist or mechanical engineer(or whatever other field might have studied these forces).

 

Dano's comment on the gear select is also very possible, pretty easy to overlook if you're not if you haven't come across a similar situation previously.

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There is likely an issue with the gun, but not necessarily. My brushed waukee gun could undo skeeter lugs boss man's brushless tightened. I don't think he went too overboard though. There are dozens of other variables as others mentioned. Static fastener torque will always be different than when you are tightening and tightening torque does not equate to loosening torque for a number of reasons. Part of it is Newtonian physics as was mentioned earlier. If you are pushing a couch you can get a running start with two people and one person can let go and get on the couch and the other will have no problem moving it, but if you stop you might not be able to get it to move again by yourself. You can get that fastener moving without any load and keep it going as the load builds and put an insane amount of torque on it if you don't stop. If you have ever done any head work you know what I mean. You can't just make quarter turns with your torque wrench and expect to get a good torque because every time you go from static to dynamic torque the ratio of applied torque to actual clamping force changes completely. This is why many manufacturers actually use a low initial torque sequence and then go by degrees of rotation as it is a more reliable reference for clamping force than someone using poor technique on a torque wrench. Race engines are built with bolt stretch gauges in stead of torque wrenches on the main caps. This brings me to my next thing. After you torque those lugs a few things will happen. One is that your wheel studs that you stretched while tightening will start to try to settle and put a lot more load onto those threads, if you didn't put anti-seize on your threads corrosion will increase resistance road grime and brake dust exacerbate this, if you have alloys your lug nuts will actually embed a little into your wheels, the wheels spiing and putting a load on your wheels does something I'm sure (always retourque lugs after driving), and finally you may have cross threaded the nuts. What it comes down to is that you should never have a situation where a lug requires enough torque to loosen that it strips it. I know those assholes on NASCAR use impacts but those boys are playing with different toys. The only time I use an impact on wheels is on semi lugs (they have cast drums) and on heavy equipment. It's not worth warping your rotors. A torque wrench is $10 at HF. Use it not because of what me or anyone else says, but because you don't want to get a flat in the middle of nowhere and not be able to get your lugs off with a standard tire iron.just my two cents. Feel free to disregard. Wish you the best of luck. I hope you don't take this as criticism, but rather just my opinion that I've formed from my limited experience and knowledge. As always take what I say with a grain of salt. 

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Yup, a lot of torque to yield bolts nowadays...but lug nut studs aren't torque to yield so when you overtorque, something has to do something it's not designed to do. My hypothesis; the wheel deforms until it can't any longer then the bolt stretches(Often this leads to sheering). Just be glad you didn't get to that point, changing those studs are a pain in the ass, especially on the rear.

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That impact wrench has enough torque to tighten a nut down, stretch the bolt, start threading the stretched part, freeze everything, and finally snap the whole thing off.  Most likely you're in the middle somewhere pretty close to a cold welded lug and it's going nowhere in a hurry.

 

The other possibility is there's an issue with the impact wrench or socket. The ~1100 ftlb torque from the impact would equate to about 370 lbs of force on your breaker bar so unless you got more than that it's quite possibly an issue with the impact.

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Man put some antiseize on those lugs and you wont have that issue.

 

Also lugnuts tend to be soft and crappy make sure you replace the ones that look goober'd,you may have threadlocked them. Get a nut buster and break the nuts.

 

Id send that puppy in to have it looked at(the impact wrench).

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