"My Dewalt DCD785 was not running true and had a noticeable wobble; I decided to have a go at changing the chuck. The new one runs true, grip on bits seems better and was easy to install. It is a noticeably heavier than the plastic sleeved one that came with the drill. This is the chuck that comes with the top of the range DCD985 and DCD995. It came with some marks as it is not secured in its packaging.
To remove the previous chuck on these drils, one needs a long T20 torx to undo the screw inside the chuck, which is removed by rotating the tool clockwise (the screw is reverse threaded). Removing the old chuck is the hard bit, as the factory assembly is tight. A 300mm ratchet with a 10mm hex bit on did it for me (set the drill in drill mode, on the highest gear for best braking). The chuck should be rotated anti-clockwise as it is mounted on a forward thread.
For reassembly, just screw the new chuck in(by hand, you can use the drill to do the work), add threadlock to the old mounting screw (or change it if required -- my staple threadlock is Loctite 243), tighten it in some, tighten the chuck with the tool you used to remove it, do the final tightening of the securing screw (anti clockwise, reverse threaded, remember) and check that it all works."
"Appears solidly built. Haven't given it any punishment yet. I've put it on a Bosch 750w hammer drill where the original chuck had jammed after a lot of drilling for 7mm holes in hard brickwork:) So it is not a perfect fit, not sure the Bosch one would have been any better as it didn't look the same as the original. Anyway the gap between chuck and body)doesn't bother me. I've rated this as 3/2 stars as I haven't really had the chance to test it. I expect my kit to last years as I have no desire to waste money or prop up cheap manufacturing nations."