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Driving piston will not return on Dewalt framing nailer


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Hey, I need to get my framing nailer working again asap. It is a Dewalt D51844. I am not entirely sure how the driving piston is supposed to return, however, it fires but wont return without being pushed back up. I've oiled the piston shaft and checked the o rings on the piston head and in the trigger assembly. Occasionally after firing it it will blow off air from the tip and slowly return back up with a comically long delay. The gun also started firing nails out uncontrollably upon connecting it to the compressor once and only once...


Any diagnosis or ideas? 


Running it at ~110psi with 22 degree plastic collated nails. 


This issue arose after driving at least 1000 nails without a problem. 

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  1. Trigger Valve Assembly
    • 1

      Disconnect the gun from the air hose. Locate the roll pin directly above the trigger. Lay the gun on its left side and use a small metal punch and ballpeen hammer to drive the roll pin out, until the trigger mechanism is loose. Remove the trigger to expose the front of the trigger valve.

    • 2

      Pull the valve assembly from the nailer's handle, pulling toward the tip of the gun. Inspect the valve and O rings, looking for wear on the rings and cracks or splitting in the plastic valve. If the valve appears undamaged and the trigger has been easily returning to its original position after firing, replace only the O rings. If there is apparent damage to the valve, or the trigger has malfunctioned, replace the entire assembly.

    • 3

      Fit new O rings onto the valve body and apply oil to the rings with a cotton swab, or apply oil to the rings on the new valve, depending on your repair option. Fit the valve back into the nailer handle, aligning the grooves on the valve with the opening for a proper fit. Press the valve all the way in.

    • 4

      Fit the trigger back in place and use the metal punch and hammer to reset the roll pin, with gentle taps, to move the pin slowly to avoid bending the pin or damaging the head. Reconnect the air hose and return the tool to normal use.

    Driver Cylinder Service
    • 5

      Disconnect the nailer from the air hose. Remove the four screws holding the square vent to the back of the gun. Use an allen key and turn the screws counterclockwise to remove them. Lift the cover from the rear of the gun.

    • 6

      Push a thin metal rod through the fastener port in the tip of the gun to push the driver cylinder out the back of the gun. Inspect the cylinder and O rings as previously outlined for the trigger valve. Inspect the metal driver as well, looking for bends, grooves or rough edges. Replace the O rings, the O rings and cylinder or the O rings cylinder and driver, depending on the damage you find.

    • 7

      Insert the cylinder into the gun. Align the notches to the nailer body for correct fit and press the cylinder all the way home. Reinstall the rear vent and install the four mounting screws, tightening them with the allen key. Reattach the air hose and return the gun to normal use.


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