its not a "little yellow o ring". its thin, yes, but to use your pic, it goes right here, ( see arrow drawn on your pic) the arrow is pointing at the groove there.
yes i get that there is still play in it, but like i asked, where does it feel like the play is? pay attention next time you jiggle it.
if you took the axel shaft out of the axel, there is a special tool for putting it back in. YOU NEED TO USE IT.it does two things.
first, it drives that big a$$ seal on the end of the axel shaft. i mean its stupid easy to put on. if you did not use the tool for that seal, you probably messed with it for a while before it went back on.
second. it sets the depth of how far you can drive the axel shaft back in the axel, and where the new seal seats inside, thus where the u-joint is. if you just wing it, its either in to far, or not far enough. either way, it will DRASTICALLY reduce the life of the little needle bearing, AND the lock out. picture a straight line being drawn between both of the ball joints. that u-joint needs to be dead center in that line, or when you turn the wheels it will force the axel shaft off center in the needle bearing and lock out.
i asked for the picure of the axel shaft, cuz your pic didnt show me what i wanted to see. where that little needle bearing rides on that axel shaft, if it is in any way wore down, not the same diameter as the rest of the shaft between there and the splines on the end, you need a new shaft, or there will always be play, and decrease the lift of the needle bearing, seal, and lockout.
i know these things, because i bought two new wheel bearing assemblies $5-600 x2, two new axel shaft $225 x2, 3 new seals $65 x3, and 2 orings $5 x2, not to mention the down time, and cussing and swearing at my truck, all in 3k miles, before i got it right. i have friends at my local ford dealer. they loan me special tools. i just happened to ask one day if there was a special tool or something i was missing/doin wrong. they handed me the tool, and havent had a problem since. 45k and ticking.
also, you need to put your own grease inside that needle bearing. it comes packed with enough to not rust, thats it. every time you do brakes, take that wheel bearing assembly off, it takes like 2 mins to get it off, and repack that needle bearing. you will thank me, trust me. it will be starting to get dry. also dissassemble the lockout, if possible. i have manual ones, so mine are easy.
also, you know that there is a right way and a wrong way to put those three washers on, that go right behind the c-clip? i think there is two fiber washers and a steel. the round fiber washer, has a bevel cut on one side. if you look at the axel shaft, there is a bevel on it, those two go together, bevel to bevel. then the steel, then the fiber again, then the c-clip.
its also my experience, that when you do wheel bearings, you also do lock outs. i have manual lock outs. there cheap. but think about it. your wheel bearings have xx,xxx miles on them. so you change them. your lockouts also have xx,xxx miles on them. your lockouts are what holds the other end of that stub axel shaft. there is also a bearing inside the lockout. if your new on one side, but wore on the other....... i put new ones on, and saved the old ones for spares.