Nailer Not Sinking Nails? When to Replace the Piston Driver

In a pneumatic nailer, the piston driver is the piston and the steel blade attached to it. Every shot, it slams down and drives the nail. Over thousands of shots the blade tip wears, chips or bends — and the nailer starts leaving nails proud of the surface.

Symptoms of a worn driver

• Nails aren't sunk flush, even with the depth adjustment at maximum and correct air pressure.
• Nails come out bent or drive in at an angle.
• Frequent jams in the nose.
• The driver blade doesn't return fully after firing.

Rule out the easy causes first

1. Air pressure: check the compressor regulator is set within the nailer's rated range.
2. Depth setting: make sure the depth adjuster isn't set shallow.
3. Nails: confirm the nail length, gauge and collation angle match the tool.
4. Lubrication: a few drops of pneumatic tool oil in the air inlet, if your nailer's manual calls for it.

If none of those fix it, inspect the driver.

Replacing the piston driver

1. Disconnect the air hose and remove all nails from the magazine.
2. Remove the cylinder cap. Undo the bolts on top of the tool and lift the cap off. Note the order of the gasket and any parts underneath.
3. Pull out the piston driver. Inspect the blade tip: it should be flat and square. A rounded, chipped or mushroomed tip means it's worn.
4. Check the bumper. The rubber bumper at the bottom of the cylinder absorbs each shot. If it's cracked or flattened, replace it at the same time.
5. Lubricate the new piston's O-ring with a little pneumatic tool oil and slide it into the cylinder.
6. Reassemble the cap and gasket, tightening the bolts evenly.
7. Test on scrap wood before going back to work.

Finding the right driver

Drivers are specific to the nailer model — framing, finish and roofing nailers use very different drivers even within the same brand. Match the part number (for example 885-918 for several Hitachi / Metabo HPT framing nailers) or your nailer's model number against the Compatible models list on the product page.

Safety: always disconnect air before working on a nailer, and wear eye protection when test-firing.