So how do I tell if my rear end is bad. Getting a bad shudder between 35 and 50mph. Took the cover off tonight and there seems to be some play between the four spider gears more on top and bottom than the side ones. Also seems to be a little play between ring and pinion. the spider gears are worn but seems that the are worn evenly but they do seem a little rough to me.
By the way this is a 8.8 in a 96 f-150 136k rear probaly has never been touched. could the shudder be from the spider gears or maybe the clutches. Also I know the shudder is from the trans back just not sure where. Also there is a thud coming from the rear end sometimes on take off a real solid thud. It has new tires and the u joints are good. any help will be great.

 

put the truck in neutral, block the tires, and then turn the driveshaft back and worth, you should have minimal play, maybe 1/4 inch turn, if that, but one thing that makes me wonder is if it were the rear end, wouldn't it just get worse as speed increaes? How are your u-joints? When the u-joints were going bad on my 78 f100, i would get a vibration at higher speeds, and then a thud when you stoped or started to drive. Do you have a 2 peice driveshaft or a single? Could be the carrier bearing if it is a 2 peice.

 

the u joints are good but that is what the thud sounds like.
As for the shudder it doesn't do it when accelerating or slowing down only when cruising not going any faster or slower and it only happens for a short time and it is not constant. That is what is leading me to beleive it is the rear end.

 

I have the same problem. Where to start fixing is a big issue. Do you do the junkyard or the rebuild?

 

do you also have limited slip

 

136k mi leads me to believe the bearings are going. The play on the ring/pinion is fine, that's backlash (shouldn't be excessive though) and can be measured with a dial indicator. Probably time for a rebuild (about 80-90 in parts if you don't change all the gears). Take the driveshaft off and check for any play in the companion flange (the face that the driveshaft is mounted to). You should also take the tires and drums off to get a better feel for what the differntial is actually doing.