Impact Driver Not Impacting
The tool spins, but the familiar hammering never starts, or it clatters weakly and the screw barely moves. Often nothing is broken. Here is how to tell normal behavior from a real fault, and what to do about each.
If your impact driver is not impacting, first check that it is actually under load: impact drivers only hammer when the fastener resists. A light screw in softwood never triggers impacts. Next, check the mode (low and assist modes limit or delay impacting), the battery charge and the bit. If it spins freely under heavy load without hammering, or hammers weakly with a full battery, the hammer spring, cam balls or grease are likely worn. That is a service or warranty job.
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First: an impact driver only impacts under load
This is the most common "fault" that is not a fault. Inside the tool, a spring holds a hammer against the anvil. While resistance is low, the two turn together and the tool acts like a fast screwdriver, fairly quietly. Only when the fastener resists hard enough does the hammer slide back against the spring, spin past the anvil lugs and strike. That is the clatter you expect. The full mechanism is explained in how an impact driver works.
So a 1-1/4-inch screw into pine, a small drill bit, or a bolt that is already loose may never trigger impacts. To test the tool properly, drive a long screw (3 inches or more) into a solid piece of lumber on the highest setting. It should start hammering well before the head seats.
Impact driver not impacting: quick diagnosis
| Symptom | Likely cause | Fix |
|---|---|---|
| Spins, no hammering on small screws | Normal: not enough load | Test with a long screw in solid lumber |
| Starts slowly, hammers late or softly | Low speed, assist or self-tapping mode | Switch to a higher speed setting |
| Weak, slow blows; stalls on lags | Low or worn battery | Fully charge; test with another battery |
| Impacts but fastener barely moves | Bit or adapter absorbing energy, wrong fastener size, no pilot hole | New impact-rated bit, shorter stack, pilot hole |
| Stops mid-drive and restarts after cooling | Overheating protection | Let it cool; use a bigger battery and pilot holes |
| Spins freely under heavy load, never hammers | Broken hammer spring or worn cam | Service or warranty |
| Hammers weakly with a good battery, getting worse | Worn spring, dried or contaminated grease, worn anvil | Service or warranty |
| Grinding, rattling, metallic crunch | Internal damage | Stop using; service |
Step-by-step checks, easiest first
1. Check the mode
Speed 1 on most tools caps motor speed, which makes blows softer and less frequent. Assist modes run slowly until a screw bites. Self-tapping and T-modes deliberately limit or delay impacting to avoid stripping. Reverse auto-stop modes stop the tool once a fastener loosens. If you or someone else changed the mode, the tool may feel broken when it is behaving as designed. Set it to the highest speed for testing. The modes are explained in impact driver speed settings.
2. Swap the battery
Use a fully charged pack, ideally one you know is healthy. A worn battery sags under load, slowing the motor between blows, and the tool may cut out altogether. Also check the battery latches fully and the contacts are clean. If a different battery fixes it, the old one is the problem; see the impact driver battery guide.
3. Check the bit, adapter and fastener
A rounded bit cams out before torque builds. A long extension, a loose socket adapter or a wobbly bit holder soaks up blow energy. Try a short, new impact-rated bit directly in the collet. For lag screws, make sure the pilot hole is the right size: no pilot in hardwood can make any tool look weak.
4. Rule out heat
Brushless tools protect themselves by cutting power when the motor, electronics or battery get too hot. On heavy lag work this can look like a loss of impact. Let the tool and battery cool. If it happens often, read impact driver overheating.
5. Listen to the mechanism
With the battery in and the bit free, run the tool briefly. Then drive a long screw. A healthy tool spins smoothly, then gives a crisp, even hammering. A dull, irregular or grinding sound, or a tool that spins freely while the screw stalls, points inside. The sounds and what they mean are covered in impact driver noises explained.
Internal causes: spring, cam and grease
If the basics check out, the impact mechanism itself is the suspect.
- Hammer spring. It pushes the hammer back into the anvil after each blow. A broken or fatigued spring means weak or no blows.
- Cam and steel balls. The hammer rides on balls in angled grooves on the spindle. Worn grooves or balls stop the hammer from cycling properly.
- Grease. The mechanism runs in grease. Over years of heavy use it dries, thins or gets contaminated with metal particles, and blows become sluggish.
- Anvil and hammer lugs. Worn or chipped strike faces reduce the energy transferred.
Some experienced owners open the hammer case, clean and regrease it, or replace springs. Parts and grease specs vary by model, and many are not sold to consumers. Opening the tool can also void the warranty. For routine care that does not require disassembly, see impact driver maintenance.
Safety: Remove the battery before inspecting the collet or opening anything. Do not keep using a tool that grinds or binds internally; broken parts can lock the spindle suddenly.
When to stop and use the warranty
If the tool spins freely under load, hammers weakly with a known-good battery, or makes grinding noises, stop troubleshooting. These are internal faults and usually covered when the tool is in warranty.
- Milwaukee lists a 5-year limited warranty on most M12 and M18 tools.
- DeWalt lists a 3-year limited warranty, plus 1 year of free service and a 90-day satisfaction guarantee.
- Makita lists a 3-year limited warranty.
- Ryobi lists a 3-year warranty on many ONE+ tools.
Terms change and some require registration, so check the current terms on the manufacturer's site and keep your receipt. Authorized service centers handle repairs; outside warranty, compare the repair quote with the price of a bare tool.
Prevention
- Use the right setting for the fastener rather than full power on everything.
- Pilot-drill large lags so the tool is not hammering for long stretches.
- Use impact-rated bits and short accessory stacks.
- Keep batteries charged and store them cool.
- Do not use the tool as a hammer or drop it on the anvil.
- On heavily used older tools, consider periodic professional servicing of the impact mechanism.
If you often need more than your tool gives, the issue may be the tool class, not a fault. Hydraulic drivers, for example, behave differently; see hydraulic impact drivers explained.
Frequently asked questions
Why does my impact driver spin but not hammer?
Most often because the fastener is not resisting enough. The hammer only disengages and strikes once torque exceeds what its spring holds. Small screws and drilling often never reach that point. If it spins without hammering on a lag screw that is clearly stalling, the mechanism needs service.
Can I fix the impact mechanism myself?
Experienced users do regrease and replace hammer springs on some models, but it requires disassembly, the right grease and parts that may not be sold to consumers. Opening the tool can void the warranty. If it is in warranty, send it in instead.
Does a low battery stop an impact driver from impacting?
A weak or nearly empty battery reduces motor speed under load, so the hammer strikes softer and less often. Lithium-ion tools may also cut out under heavy load when the pack is low. Always test with a fully charged, known-good battery.
Is it normal for an impact driver to impact when drilling?
It only impacts if the bit binds. When drilling with small hex-shank bits the tool usually just spins. Larger spade or auger bits can trigger impacts as resistance builds, which is also normal.