Impact driver losing power ... WTF?

I've got a Milwaukee cordless impact driver that cost me close to $400 a few years ago. I pretty much use for only one thing: removing nuts when swapping/rotating wheels at the track. It used to zip off the nuts instantly, which is no surprise because it's rated for something like 1400 ft-lbs of torque.

Lately, it's unable to crack wheel nus ... that were hand torqued using a calibrated torque wrench set to 88 ft-lbs. There are two batteries. With either battery, even fully charged, this thing is making no power.

What do you guys think? Just old batteries, or is the driver itself to blame?

I'm curious about this as well, as my little Milwaukee stubby (~250 ft-lbs) won't break wheel nuts torqued to 90, even with a fully charged 4Ah OE battery.

I've had this issue with a Craftsman i bought.  With mine it was the battery, the OE's ones for those were crap.  I imagine they degrade over time.  Upgraded to a Li-Ion battery, and it didn't blow up.  No problems with lug nuts anymore. 

I'd try torquing something down with the impact, then use the torque wrench to verify torque.  Then I'd measure amperage and voltage of the batteries.

Keep in mind that breaking an 80 lb-ft nut loose requires way more than 80 lb-ft.  Friction vs. Sticktion.  Torque ratings on impact-type drivers are also pretty bogus.  If it actually created 1400 lb-ft of torque, you'd be in the hospital.  Torque ratings in impact devices are measured by the moment of inertia generated by the anvils and the radius of the orbit of the mechanism.  Sure a 4 oz weight spinning at X mph mathematically suggests big numbers.  In truth, that torque is only applied for a miniscule radian of the rotation and that's why they advertise it at "peak" torque.  Much like your 6hp "peak" shop vac.  6 hp would actually require about 4500w, or about 40A, and yet they run just fine on a 15A shop circuit.

I would blame the batteries.  They have a limited life.  Everything in there has a limited life; motor, anvils, switch, but the battery is the most likely culprit.

Mine will torque the nuts to spec but I usually have to break them loose with a breaker bar.

I've seen this myself with my older 18V DeWalt 1/2" impact. It's better with the 20V batteries and the adapter, but still struggles.  If I know I'll be doing a full set of tires, I just drag out the air gun. My IR 2135ti hasn't met a nut or bolt it couldn't loosen.  Plus, when I'm swapping seasonal tires, I usually have to top off the air in them anyway.

Ian F (Forum Supporter) said:

I've seen this myself with my older 18V DeWalt 1/2" impact. It's better with the 20V batteries and the adapter, but still struggles.  If I know I'll be doing a full set of tires, I just drag out the air gun. My IR 2135ti hasn't met a nut or bolt it couldn't loosen.  Plus, when I'm swapping seasonal tires, I usually have to top off the air in them anyway.

My old 18V NiCad Milwaukee 1/2" driver (from around 2002) would usually get lugnuts off if the batteries were fully charged and relatively new.  A few years ago all the batteries I had for it were dead so I replaced it with an 18V lithium model and it is noticably stronger and never has issues getting lugnuts off.

I did need to break out the Ingersoll Rand for the FD's flywheel nut though!

My Makita never takes more than 2 pops to loosen a lug nut, and that's on the lowest setting.  It also feels like it weighs about 30 pounds and is generally a PITA to use for anything except lug nuts, but power has never been an issue.  I've had it for 3 years and haven't noticed it losing any power.

How old is it? If it’s the old NiCad version, it could be worn batteries. If it’s Li-Ion, those should work at full power until it just stops. A worn battery won’t work as long, but should work fine when charged, or it just won’t charge. Any other wear? Extra play between the tool and nut drastically cuts effectiveness of an impact, since it just shakes the play in the joints back and forth instead of transferring the energy to the nut. Check the sockets, nuts, and any extensions for excessive wear. 

I would suspect the batteries, what AH are the batteries you're using? As an example, I have the Milwaukee 2767-20, and I use the 5.0AH batteries.

It's probably the NiCad batteries. From very first charging they start losing there ability to fully charge. Some people say you should not short charge NiCad batteries and only charge when they are fully discharged. Seems NiCads do best with constant use and sitting for long periods of time allows them to degrade. I have replaced most of my NiCads with Lit-Ion and they hold charge longer and have better power. 

I would suspect batteries as they do break down over time. There appears to be a proper Milwaukee dealer in Flushing and they may be able to test the tool/batteries.

Take the head apart and make sure everything is clean and lubed.

My Craftsman C3 got rusty internally over the first winter I owned it.  It just sucked.  I pulled the nose apart and cleaned a whole lot of rusty gick out, and relubed it. After that it was much better, but I still had to torque my lug nuts to 60 so the gun could get them back off.

I have a Bauer now, it stays in the house over winter.

pirate said:

It's probably the NiCad batteries. From very first charging they start losing there ability to fully charge. Some people say you should not short charge NiCad batteries and only charge when they are fully discharged. Seems NiCads do best with constant use and sitting for long periods of time allows them to degrade. I have replaced most of my NiCads with Lit-Ion and they hold charge longer and have better power. 

The "memory effect" on NiCad batteries, while real, isn't something you're likely to encounter in real-world usage.  AIUI it showed up in satellites where they would have a very regular charge/discharge cycle due to the orbit and solar panels.

But yes, NiCad is effectively obsolete at this point, lithium ion is just generally better for power tools.

Check the interwebz as it is far cheaper to send batteries off to be rebuilt than to buy new.

Mine still rips axle nuts, and lug nuts with ease after about 5 years.   Is yours brushless?

It uses "M18" batteries...pretty sure they're lithium ion. But I'll check when I get home.

79rex said:

Mine still rips axle nuts, and lug nuts with ease after about 5 years.   Is yours brushless?

It's more about charge cycles than raw age.

Just checked. They are indeed lithium batteries, for whatever that's worth

In reply to Ian F (Forum Supporter) :

Over the weekend, I rotated the tires on the minivan and the DeWalt had no problem with removing 20 lug nuts as well as a few bumper support bolts for a hitch receiver install. It was a fresh battery just off the charger. So who knows...