While driving back home from a road trip, I started to notice a "whine" at higher speeds and only when under acceleration/load. I'm pretty sure it is coming from the rear of the truck. Is there anything I can check? The truck is under warranty still but I would like to have an idea before they try to BS me on something that won't solve the problem. Any ideas? Truck has stock gearing, 4WD, BFG AT KO's.

 

Most likely it is pinion bearings. I would just take it in because it is under warranty and if you tear into it, they may blame you. Let them deal with it!!

 

Same thing happened to me. They replaced entire axle.

 

Thanks guys. Do you think they can/will hassle me about the slightly larger tires on the truck? I'm supposed to take it in later this week.

 

OK, so I just got off the phone with the service department and it turns out the warranty ran out on my truck roughly 5000 miles ago. Crap. So I asked him how much to just check everything out in the differential. He tells me one hour of labor and the cost of new synthetic fluid. Roughly $200. Am I going to get in over my head? I have a good friend who is a Ford mechanic that would probably do the work as a side job. Any thoughts? I'm thinking I might just take the truck in to have the rear end checked so I know what is exactly wrong and then go from there.

 

More than 90% chance it is the pinion bearings, if not, all new bearings will
fix it anyway.
You can get all the bearings and seals (including wheel) for about $100.00
at an auto parts store, oil is about $40.00 for the good stuff.
Since you would be going back with the same ring and pinion you would
require no setup tools, just use the same shims in the same location,
all three of them.

You would be wasting your $200 by getting the FORD Guys opinion.

Just pay your friend to do it.

 

Took your guys advice and had my friend do it as a side job, replaced the pinion bearings and appropriate seals. The sound is gone. I was amazed at the little bit of wear that caused the gear whine sound. $300 bucks for everything. Can't complain. Thanks a lot guys