It started at only 3,000 miles with a loud clunk every time I'd switch from 2wd to 4wd. After changing back to 2wd it would stay in 4wd and clunk loudly after it would switch back, It wasn't immediate. At 13,500 miles it started clunking really loud. It would only clunk loudly at 2wd. It would stop at 4wd. Dealer wanted me to leave it there for four days. Instead I bought it for $130. Information I got when I bought it was that they had over 30 in stock. This is the same part that the 2008+up F150's have. Very problematic part is made out of plastic. When I removed it, it was broken. I replaced it and the problem stopped. It doesn't clunk at 2wd. The problem is still present. Now it only clunks when under load or acceleration in 4wd. It is annoying and I'm disappointed with the quality of my truck. At first I was thinking that this was due to the 21/2 inch leveling kit I installed but I remember the clunking started before the leveling kit was installed. I love the truck but I'm deeply disappointed simply because this is a recurring problem since 2008. I assumed the problem would have been fixed by 2015. It wasn't. Now I hate my truck. Worst purchase ever.