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Let's talk impact wrenches and their torque specs

 
Old 03-10-2019, 10:56 AM
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Default Let's talk impact wrenches and their torque specs

Hi folks, I've always struggled to understand impact wrenches and their published torque specs in how they relate to breaking loose a bolt.

For example, I know most of bolts on the suspension parts of our JK are torqued at 120 ft-lbs or less. Additionally, I typically torque my lug nuts down to 110ft-lbs. I know most of the impact wrenches out there tend to hype their torque rating where they tend to publish those max torque and break away torque ratings under some ideal condition which is typically not real world. I had originally thought if I get an impact wrench which was rated at 240 ft-lbs of break away torque then even with hyped numbers that is still 2X the rating of a 120 ft-lb tightened bolt and I should be able to bust loose a 120 ft-lb torqued down bolt with an impact rated at 240 ft-lbs.

Is there some cross reference chart or general rule of thumb to go by for the minimum torque rating an impact wrench should have to bust loose a particular ft-lb torqued bolt?

I was recently watching this guys review video of the HF Earthquake XT 1/2in impact wrench. (WARNING! NON KID FRIENDLY LANGUAGE!)

So one thing he seemed to be describing was for an impact wrench which was rated at 1200 ft-lb, it should be able to remove a bolt which has been torqued down to around 400ft-lbs. I wasn't sure if he was referring to some cross reference chart but what I noticed is that he seemed to just divide by "3". So if a impact has a max break away rating of 1100 ft-lbs then it should able to bust loose a 1100/3= 366 ft-lb torqued down bolt. Is that a general rule of thumb or just a coincidental observation I have made?

What gives, how do you figure this out besides purchasing the largest torque rated spec impact you can afford and just checking to see if it breaks a particular bolt loose?
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Old 03-10-2019, 10:57 PM
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You ask a very good question. I'm not certain there is a great answer, but subscribed to see if there is some enlightenment here. I'd add that I bought the pneumatic version of the Earthquake this last year after years and years of using cheap POS things. I got damn tired of having to use a breaker bar on bolts/nuts that the old units should have easily broken free.......like you're alluding too. I'm really happy with the unit. It's definitely not a cheap POS HF tool IMO. You have to be careful with it too....cuz even on the lowest setting you can jack something up........

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Old 03-11-2019, 03:48 AM
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So full disclosure of one of the reasons I'm asking.
When I purchased my lift and started installing it, I didn't have a lot of funds at the time after purchasing all the suspension to be investing in the best tools available. However, I knew a 1/2in impact wrench was likely going to be handy. I therefore, purchased the HF Chicago electric 1/2in corded impact for $40.
https://www.harborfreight.com/12-in-...nch-68099.html

Overall, it served my needs. My measuring stick was that if it was able to break loose my lug nuts which I torque down to 110 ft-lbs and didn't burn up in the process then it fit the bill of what I needed. That impact was rated at " Delivers 230 ft. lb. of max torque".

Later on down the road after fighting with getting the extension cord caught around my tires I decided it was time to start looking at investing in some cordless tools. At the time most of my cordless tools were using the NiCad batteries which didn't last very long and were expensive batteries to replace as well as the chargers weren't cheap either. So it was time to replace the old NiCads with new Lithium battery tools. What I learned through my experience with the NiCad battery tools is that the quality of the tool was secondary, you were really investing in the eco battery system of replacement and backup batteries. My Craftsman and DeWalt NiCad cordless tools still worked great, the cost of the batteries and chargers seemed very unreasonable. After shopping around looking at the costs of different brands of cordless tool Lithium batteries, I decided to go with HF's "Bauer" brand tools, mostly based on the cost of the replacement batteries which were using Samsung Lith-ion cells. The cost of additional chargers were only $20 as well. So when HF eventually came out with the Bauer 1/2in cordless impact and it was rated at "delivers 450 ft. lbs. breakaway torque" it seemed like it would be a good fit for my needs. Afterall, the Chicago electric was rated at 230 ft-lbs and I was just looking for a cordless version that would be able to break loose my 110ft-lb torqued down lug nuts for added convenience. Much to my dismay, the Bauer impact was not up to that task of breaking loose 110ft-lb lug nuts. I should have returned that tool but decided to hold onto it anyway. I was already invested in the Bauer battery eco system, so I was just out $85 from the Bauer impact purchase but figured I could still put it to use.

Bauer impact:
https://www.harborfreight.com/20V-Hy...nly-63629.html

It seemed if I needed a cordless option that was stronger from HF, then I would need to step up to the Earthquake XT 1/2in which was $240(sale price).
https://www.harborfreight.com/20v-ma...kit-63852.html

Which also meant, I would need to invest into yet another battery/charger eco system where I already had this going on which currently equates to 5 chargers/7 batteries of the Bauer eco system. I hate the fact that all these cordless tool brands use different chargers with differently keyed battery cases.


So now I'm thinking for the HF Earthquake XT impact it was going to be $240, plus another $60 for a backup battery. So $300+ for the added convenience of having a cordless option to spin off lug nuts? That impact is rated at "1200 ft. lbs. bolt breakaway torque" but how was I to really know if that was going to live up to breaking loose 110 ft-lb lug nuts or better yet 120ft-lb control arm bolts if needed?
https://www.harborfreight.com/20v-ma...kit-64195.html

I pretty much surrendered to the fact I was best to go with the an M18 18V Milwaukee Fuel 1/2in cordless impact if I was going into that price range to be able to spin off lug nuts on my JK. Torque rating "1400ft-lbs of nut-busting torque". So what's that going to cost me?
18V Milwaukee Fuel 1/2in cordless impact: $249
https://www.homedepot.com/p/Milwauke...7-20/302654201
(2) M18 batteries and charger: $169
https://www.homedepot.com/p/Milwauke...850P/307399442
Total estimate=$418

So $418+ to get a cordless version of what I was able to achieve with a $40 HF Chicago electric corded 1/2in impact? Seemed like a tough pill to swallow for some added convenience of getting rid of an extension cord, plus I would be starring at eventually re-purchasing some more Milwaukee expensive batteries or getting some lower cost knock-offs down the road where the knock-offs had to be ordered online. This all got me thinking, how much torque do I really need from a cordless impact to bust loose my 110ft-lb lug nuts? Maybe I need to shop for something with less torque but how to know without making a purchase and just trying it out?

Last edited by Rednroll; 03-11-2019 at 05:34 AM.
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Old 03-11-2019, 04:35 AM
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I did find a solution this past weekend which seemed to meet what I was after and still made economical and convenience sense. However, my question still remains a mystery. How much is enough of rated torque vs. actual bolt torque?

Anyways, HF had one of their side-walk sale weekends and I decided to stop in this past Saturday. Sitting on a table they had (3) Open Box Earthquake XT 1/2in cordless impact wrench sets, marked down to $193. My initial thought was that's a little better....but still "meh". Then I notice the sign hanging on the table, "Take an additional 50% off of these already marked down items." I had to ask to make sure...."So 50% off of the $193 price tag? $96.50?" Yes. Ok, now we're talking. Oh and that extra battery sitting there is 50% off as well? So $25? Yes.


So for $120 total, I seemed to have lucked out.


I charged up those batteries, and the 1st thing I did was torque my lug nuts to 120ft-lbs and tried to spin them off. SUCCESS! Like a hot knife through butter. I also confirmed the Bauer 450ft-lb cordless impact still wasn't up to the task.
Now how long is this HF POS going to last me and is it any good? That's the reason I was watching the video in my original post.

Then it was time to see if good ole infamous AVE had a review of this potential HF Earthquake XT POS.
It seems to get the nod of approval after AVE's tear-down and test run, so I guess I'll hold onto it. If it's even 50% of a Milwaukee M18 at 30% of the cost, I'm ok with that.

Last edited by Rednroll; 03-11-2019 at 05:29 AM.
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Old 03-11-2019, 06:07 AM
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Ok, I found a video by a guy who is much more familiar with impact wrenches and measuring their torques than myself. Basically, it seems to boil down to the "nut busting" or "max impact" and "break away" published torque ratings are pretty much non real-world B.S. marketing numbers since there's no established standard way for manufacturers to perform the testing/measuring. He shows how one of the Milwaukee's was able to get it's marketed packaging label "1100ft-lb nut busting torque" number by heating up the bolt. Which is actually a good demonstration as to the reason we heat troublesome to get off bolts. The heat causes less thread friction. Which to me further opens the door to if there's no standard of the bolt temp, then there's no standard for the bolt size, thread pitch, hardness, ect. which could all have an impact on the torque measurement and the amount of thread friction. I guess, the only really way to know for certain or not if an impact wrench has enough torque for you is to buy it and test it out and then return it if it doesn't meet your expectation.

Last edited by Rednroll; 03-11-2019 at 06:28 AM.
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Old 03-11-2019, 06:11 AM
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With the earthquake, can you set your installation torque? I've worried about the opposite of removal- when installing, I don't want the thing to have so much torque that the nuts or studs get damaged.
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Old 03-11-2019, 06:37 AM
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LOL, that picture of your battery set up is classic. I like the convenience of being portable, but I really hate dealing with batteries and all that kinda crap which is why I went with the pneumatic version. I can tell you that my Earthquake is enough to break a pinion nut loose, and enough to crush a crush sleeve. Probably the toughest tasks on the JK. I'd imagine that cordless version will do the same since it's the same rating. Hopefully the batteries hold up well. Be careful with it since it's a lot more power.
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Old 03-11-2019, 06:39 AM
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Originally Posted by rob_engineer View Post
With the earthquake, can you set your installation torque? I've worried about the opposite of removal- when installing, I don't want the thing to have so much torque that the nuts or studs get damaged.
No, other than price that was originally one of my concerns in getting a torque wrench with a higher rated torque. The only way you could likely limit the amount of torque during tightening on the Earthquake is that it has a variable speed wiper trigger which would be hit/miss and a PIA to try and gauge.

That must be the reason why the Milwaukee's have a 2 speed switch but then you're limited to 2 max torque settings. I had always wondered why these impact wrenches don't have an adjustable dial like on the electric screw drivers. I always found that to be a great feature to avoid over tightening screws.

Last edited by Rednroll; 03-11-2019 at 06:47 AM.
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Old 03-11-2019, 06:46 AM
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Originally Posted by resharp001 View Post
LOL, that picture of your battery set up is classic. I like the convenience of being portable, but I really hate dealing with batteries and all that kinda crap which is why I went with the pneumatic version. I can tell you that my Earthquake is enough to break a pinion nut loose, and enough to crush a crush sleeve. Probably the toughest tasks on the JK. I'd imagine that cordless version will do the same since it's the same rating. Hopefully the batteries hold up well. Be careful with it since it's a lot more power.
Yep, I've come to the conclusion for loosening bolts, you may be able to just let it rip but for tightening to just slowly spin it on until snug and then use a torque wrench to tighten unless you need to use it on a crush sleeve like you mention. That was something I actually liked about the corded $40 Chicago electric. I would crank down my lugs with that and I measured it afterwards and the lugs were in the 100-120ft-lb range making things simple. Maybe putting on bolts becomes the use for the Bauer impact I got until I've had a chance to see how tight the Earthquake tightens down the lugs. I'll bust them loose with the Earthquake, and then tighten them on with the Bauer.

Truth be told for the extra chargers, I've been picking those up at HF during these side-walk sales as well. You see the 4 chargers mounted on my bench which is convenient but I have a 5th one for portability but I doubt I'll ever use if for that. Anyways, those Bauer electric screw driver sets I've picked up (2) of those for $25 ea via open box discount sales. I figured the chargers are normally $20/ea and the 1.5mAH batteries are $20 each, but with that screw driver set I've been able to get both for $25 with another screw driver to boot during their open box sidewalk sales.

Last edited by Rednroll; 03-11-2019 at 07:07 AM.
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Old 03-11-2019, 08:32 AM
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I'm really excited to read through this thread and I'm replying here now only so I won't forget. I've had an unbelievable time with the front diff pinion nut just trying to change the stupid seal. I bought an IR big-time, million-lbs-of-breaking-torque impact which just sits there and hammers away. Just like the battery impact. It's actually on my list to do within the next few days because I'm sick of parking over a drip pan and my garage smelling like gear oil. Thanks in advance for everything I'm gonna learn here as soon as I get enough work out of the way!
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