Hex drills and bits weren't staying in my M18 Impact Driver. I mean the the drill got left behind in the hole and bits fell out. I got this earliest M18 Model 2650 back in 2009. There's been a whole lot of models since  Looking into things, all I could find was a few videos from this fella.

First video talked about bending the Spring (FIG.39)  to adjust contact with the Steel Balls (FIG. 37). Not only is that Spring different than mine, it sounded like it was a failure common to that particular model. Mine was fine for 13 years. Seemed this didn't have anything to do with me. I was thinking of getting on here at Tool Talk and asking for help.

But then I found the other video from this same fella told a different story. He said the two Steel Balls (FIG.37) that fit into the Anvil (FIG.36) are at fault. They wear out. He had another M18 on his bench and demonstrated how to swap em out; 3.5mm same as mine. I checked a certain online parts purveyor and I found that them FIG. 37 Steel Balls go for a few cents shy of $6 for just the two of em.

But I found this little 590 set of assorted sizes of SS balls; 50 alone for the 3.5mm, for a little over $6. You can see in the picture of the Anvil (FIG.36), one of the installed Steel Balls  and the old ones laying there. That tiny Retaining Ring (FIG. 41) was extremely difficult to get off and back on again. My Channel Lock Retaining Ring Pliers were of no use. I made a mistake reassembling and thought for sure this time I'd have to come here for help. But I eventually got it right. I tested it and the bits stay in tight.

I love it when  you can actually fix something!

I have several projects that I have diagnosed but.....

skipskip,
Yeah, me too. I reckon  it's sort of like subsistence hunting. Doing things yourself. And sometimes the more meticulous things get, the more enjoyable it is. I said sometimes.
All these  M18 impact driver models differ some. Still, it seems they share the same cause of the same darn problem.

One of my M12 impact drivers had a similar issue.  On it, the bits wouldn't pull out (cheap non impact bits).  I disassembled the front end & the balls were deformed.  Got 100 replacements on Amazon for next to nothing.  Not a fun job, but no problems since.