In-depth walk through of how to fix a non-working headlight adjuster on a 15-17 Ford F150 (may work for other models too). Also, how to modify your headlight housing for aftermarket LED headlight bulbs with cooling fans for full beam adjustment range.
I didn't explain fully in the video, but the reason the adjustment rods pop out when over-adjusted in the down direction is because the retainer can't hold the pressure. It's either a fail-safe from the factory so you don't break it beyond repair (this is most likely), or just not robust enough to hold much pressure being plastic. The added retaining washer is essentially just a much stronger rod retainer.
***PLEASE NOTE: once you do this retainer fix, the rod will no longer slip through the factory retainer when over-adjusted. This means if you don't stop when you feel increased resistance, you could break the rod or strip the plastic threads in the adjuster. Better than not having any adjustment at all, but please pay attention when adjusting.
Thanks for watching!