Hey guys, 1999 F150 4x4 5.4 V8. Been noticing a roaring noise from the rear end lately but tonight it just went crazy. Coming off of the highway and and it became extremely loud, vibration and even clunking sounds. Curious on what this could be. I was thinking bearings but I am not quite sure. Thanks in advance. -Tyler.

 

Hopefully its the outer axle bearing and not the inner carrier bearings that are the issue, but from your description, I suspect the carrier bearings. Get the wheels off the ground and check for slop/play in the outer bearings first. If they're OK then get the diff cover off and have a look. It will be pretty obvious because the oil will be full of metallic particles and the gears will be somewhat chewed up from running out of alignment due to the faulty bearings. If it is the carrier bearings and the gearset is damaged, you may be better off finding a decent used rear end at a salvage yard and swapping it out. I'm guessing its an 8.8 inch axle.

 

Yes it's an 8.8

 

I think I will just find a whole new rear end for it. Does it need to be an 8.8 or will a 9.75 work too?

 

I don't know the answer to that question. The potential issues are driveshaft length, parking brake cable connections and brake line fittings.