I have a '96 F-150 that is making a noise in the rear differential. I believe I did some damage a couple months ago when hauling a load of wood. I had a blow out on the drivers side rear tire a little while before I hauled the wood and had not gotten a new set of tires. The spare was still on the truck which was the original size tire. The tires that had been put on it was just slightly larger than the originals but on the original rims. Well I had a really heavy load on the truck and about half way home I smelled something getting hot so I pulled over. When I crawled under it the rear end was so hot I couldn't touch it. I was afraid to drive it on home so I drove it a little further to a place we could off load the wood to another truck and then drove home. I drove it a few days after that and there seemed to be no problem (no noise from the rear end) so I thought it was ok. After putting on a new set of tires a few weeks ago I noticed a "whining noise" and thought it was just the new tires but it gradually got worse. I think it is the bearings in the rear end, I have never worked on one so my question is is this something I can do myself or should I let a mechanic do it.

 

I just had to replace my Rearend with a junkyard unit because of a bad pinion bearing... Get a piece garden hose or rubber tubing and jack the truck up on jackstands and have someone put into gear and put the hose up to parts of the rear end and listen

 

Just pull the cover off and check the condition of the oil. That'll tell you more than anything. If there's an overabundance of metal flakes in it, it's probably time for a new set of bearings or even a new ring and pinion.


If it's just dark and has a small degree of metal flakes, this is normal, and you can get by with just changing the oil.


Rear wheel bearings could be due a replacement as well.


Rear wheel bearings are simple, but require a slide hammer (rentable tool from local auto parts stores). Anything relating to the differential that requires its removal is something I'd recommend leaving to an experienced pro if you've never touched one before...

 

Is is a limited slip? The clutch packs in a limited slip really aren't going to like two different size tires, but the long term result would just be that you no longer have limited slip.

An open diff (or the side and spider gears of a limited slip) might not like putting much torque for too long with different size tires either. If that's the case you've got a good opportunity to upgrade to a Truetrac or a locker!