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[rather_large_ben]

Hello all, just found this awesome site- I have enjoyed going through the "a look inside" forum! 
My problem is one of the DC720 drills I have won't lock the chuck when I let off the throttle.  This makes it impossible to tighten a bit fully since the trans and motor just spins.  I looked through the pics here and took my unit apart, but can't figure out what part inside would do the locking up~  Thanks in advance, Ben

[DEWALTDUDE]

Once a chuck goes bad, it's time to replace. Not much you can do to repair it. It's a jacob's 1/2" chuck, if it's still under warranty you can stop by a service center and get a new one. If not Home Depot, and Lowes both sell replacement chucks, and you can replace it yourself. It's pretty easy.

[rather_large_ben]

I get that you are saying it's the chuck itself that is bad, so this means the mechanism that locks the motor/trans/chuck up when the power is off is in the chuck?  You are probably right, but it's kinda weird to me that it'd be bad already since the drill is very new.  Do you know if it unlocks by centrifugal motion or something?  Thanks, Ben

[DEWALTDUDE]

I must have mis-read what you were saying? If the chuck is fine, then it's the locking pins that have either moved out of place or worn down. You have to remove the transmission.

The pins on the far left of this picture.

[rather_large_ben]

Thanks!  I will take it apart and check those pins!- Ben

[DEWALTDUDE]

Here is a part's schematic of a different drill, same application though. Look at Part #26 and #27.

Click on part diagram near the top of the page.

Link.