i have an 8.8 in my f150 5 spd. a while back when at slow speeds i could feel play in the driveline (2wd). i replaced the ujoints and it solved it. the needles were just dust. but the problem came back. and its worse. and the ujoints dont have any play. let alone the play they had when the needles were dust. so tonight or tommorow im pulling the diff cover to look there. other than obvious teeth wear, what do i want to look for? thanks

In/out, side/side, up/down play in the pinion too.

so first today i installed new ujoints and took it out for a spin. i can still feel the same play in the driveline when slowing down and traveling at idle speed in first gear. and hear the knocking of the driveline as bounces back and forth.
i pulled the diff cover off just now. the spider gears look worn to me. but i dont really know worn when i see it. the carrier only has a little rotational play, no up down side to side. i can see plenty of small glitter in the oil. the driveshaft seems like it has excessive rotational play. with both tires elevated i can turn one tire and that sides spider gear will rotate about 3/16" before it contacts the horizontal spider gears. the horizontal spider gears look to have excessive play on the centerpin. when spinning the driveshaft only, the centerpin will move alone untill it contacts the inside of the spider gear
im not sure if this is excessive play or not. it seems to me it is. if its not they something in my transmission is the problem. does it sound bad? spider gears loose on the centerpin and they have about 3/16" play

Pictures would be the bomb but it sounds like your internals are trash(too many 1 wheel spin outs), maybe bearings too. Internals make noise but normally no vibrations. Bearings on the other hand make noise and the pinion brgs cause vibrations. Lastly, if your going to run it you need to inspect and grease it. Dropping a driveline at freeway speeds is just plain deadly.

i just went down and took the centerpin out and a spider gear. here are some pictures.
http://i219.photobucket.com/albums/cc64/NetraToy/f150/DSCF1580.jpg
http://i219.photobucket.com/albums/cc64/NetraToy/f150/DSCF1582.jpg
http://i219.photobucket.com/albums/cc64/NetraToy/f150/DSCF1586.jpg
http://i219.photobucket.com/albums/cc64/NetraToy/f150/DSCF1588.jpg
http://i219.photobucket.com/albums/cc64/NetraToy/f150/DSCF1589.jpg

the spider gear has some pitting on both sides of each tooth. and some pitting on the inside of the shim. the sider gear is loose over the center pin, i can see plenty of light through it. do i have to replace the whole gear system or can i get away with something else?

the wear doesn't look excessive. look for more issues. maybe check the suspension links/bolts to see if any of the bushings are worn. I've seen similar issues when the leaf spring u bolts were too loose. the problem may be in your transmission

i also forgot to mention that when cornering 90*or more i sometimes hear a pop, which i dont think could come from anywhere else but the rear axle

You need to replace the spiders, crosspin and side gears. They should come as a set. If you can see light between the spider and crosspin, that's well past worn. With so many inter-related parts in a diff, the slightes bit of lost motion equates to huge amount of extra rotation of the pinion compared to the axles/wheels. Those gears look shot too. It may seem like the spiders fit the side gears well, but its the crosspin that connects those gears to the carrier itself.

You need to replace the spiders, crosspin and side gears. They should come as a set. If you can see light between the spider and crosspin, that's well past worn. With so many inter-related parts in a diff, the slightes bit of lost motion equates to huge amount of extra rotation of the pinion compared to the axles/wheels. Those gears look shot too. It may seem like the spiders fit the side gears well, but its the crosspin that connects those gears to the carrier itself.

thats exactly what i wanted to hear and what my gut told me. thats the second opinion i wanted. although i was kinda syked about the thought of a new axle. i wouldnt replace it with another 8.8. but my truck only has 131k on it. could never having the oil changed do that damage? ive only put 23k on it in the last year. its the first time i opend it up

it sounds like your internals are trash(too many 1 wheel spin outs.

haha has anyone here ever tried to burn out in a 4.9/m5od f150 on pavement? i tried it once and after all my exhaust hangers snapped and i thought my teeth bounced out of my skull i never tried it again

Speakin of burnin out, a buddy of mine had the same truck in high school and gave that ford hell! I don't think he kept a set of rear tires on it for more than a month. As much as I'm not a ford guy, those I-6 are a damn good motor.

the auto trans 4spd has a lowerer gear ratio for first gear. so you have more tire spin in first. a 4.9 and m5od only get 20mph wheel spin in first. which means the most voilent wheel hop youve ever experianced.

how much play can i get away with in the ring to pinion? the carrier has slight rotational play. but i dont know if its too much. id say a 16th or 3/32nds

Something else to add, but you are probably ok. The crosspin must have a very tight fit in the carrier itself at both places, or the carrier needs replaced also.