SDS Drill Not Hammering? Here's What to Check

Your SDS drill is spinning but not hammering. You're leaning into it with all your weight and the bit's barely scratching the concrete. Before you assume the drill's dead, let's go through what usually causes this.

Check the Mode Switch First

This catches everyone at least once. SDS drills have a mode selector - usually with symbols for:

• Drill only (no hammer)
• Hammer and drill (what you want for masonry)
• Hammer only (for chiselling)

If you've been using it as a chisel and forgot to switch back, or if the switch got knocked, you won't get any hammer action. Check it's in the right mode.

The Bit Isn't Seated Properly

SDS bits have to click into place. If the bit isn't fully home, the impact mechanism doesn't engage properly.

Pull the bit out, check the grooves are clean (no concrete dust clogging them), and reinsert it firmly until you hear it click. Give it a tug to make sure it's locked in.

Wrong Type of Bit

Standard SDS-Plus bits won't work in SDS-Max machines, and vice versa. The shanks are different sizes. If someone's lent you a bit or you've grabbed one from a mixed box, make sure it's actually compatible with your drill.

SDS-Plus has a 10mm shank with two grooves. SDS-Max has an 18mm shank with different groove patterns. Don't force it.

The Clutch Isn't Engaging

The hammering mechanism in an SDS drill only kicks in when you push the bit against resistance. If you're holding the drill in the air, it won't hammer - that's by design.

Put the bit against the concrete and lean in. You should feel and hear the impact mechanism engage. If it still doesn't hammer even under pressure, there might be an internal problem.

Bit Stuck in the Chuck

Sometimes an old bit gets stuck because concrete dust has packed around the shank. The chuck holds the bit but can't release it enough for the impact mechanism to work properly.

Pull the collar back and try to work the bit out. If it's really stuck, some WD-40 down the chuck and patient wiggling usually frees it. Then clean the chuck out before using a fresh bit.

Internal Wear and Damage

If you've checked everything above and it still won't hammer, the drill's internals might be worn:

• O-rings: These seal the pneumatic hammer mechanism. When they wear, the drill loses its impact force
• Piston: A worn piston won't generate the air pressure needed for hammering
• Anvil: The part that transfers impact to the bit can wear or break

If the drill's well-used and you're hearing weak or inconsistent impact, it might be service time. Quality drills from DeWalt and Makita can be rebuilt with new seals and parts. Cheaper drills often aren't worth the service cost.

Grease Level

SDS drills need proper lubrication. If the drill's been worked hard and never serviced, the grease inside can dry out or get contaminated with dust. This causes the hammer mechanism to work poorly or seize.

Some drills have grease ports for top-ups. Others need to be opened up for proper servicing. Check your manual or take it to a service centre if it's been a few years.

Quick Diagnostic

Try this:

1. Put the drill in hammer-only mode (chisel mode)
2. Hold it pointing down with a bit in
3. Pull the trigger

You should see and feel the bit jumping in and out rapidly. If nothing happens, the hammer mechanism isn't working at all. If it works in hammer-only but not hammer-drill mode, the mode selector mechanism might be faulty.

When to Give Up and Replace

If the drill is old, low-end, or been seriously abused, repair costs might exceed replacement value. A quality mid-range SDS Plus drill handles most trade work perfectly - you don't need the biggest most expensive option.

But if it's a quality tool that's given good service, a professional rebuild can get several more years out of it for less than replacement cost.