I have a 98 f-150 4wd with 4.6l v8 and 63000 mi. I get a slight whine in the rear end between 48 - 55 mph which quiets when I let off the throttle. My regular mechanic said the rear end was loose 2-3 months ago but transmission was completely gone. Towed truck Ford shop who replaced tranny (completely shot) and the in-house gear guy said the rear end did not sound bad and suggested to leave it as it is. I question this but do not particularly want to get into unnecessary repairs. Any advice?
If I must get a new rear end, am I better off replacing the nest or getting a rebuilt rear end? How much does that normally cost? I like the truck and plan on keeping it for a while. What should I look out for and could I potentially be damaging the truck taking the wait and see method?

 

Get a second opinion, have someone knowledgeable pull the diff cover and check mesh and pinion depth, some gears make noise I am finding this out

 

A slight whine that doesn't progress isn't likely to grenade. That's also not alot of mileage. Has it been routinely serviced? If it's due, an inspection is simple at that point.

 

I purchased the truck about 7 months ago supposedly well taken care of. There is not any evidence of abuse. Body and engine are in great condition. I have a hard time convincing anyone it is actually a 98, however, the drive train has been something of a problem. As posted earlier, I replaced the tranny 3 months ago. It had originally been replaced 18 months ago with apparently a defective unit. My own mechanic says the rear end is loose but he is a good engine guy but is not comfortable working with all the gears and would rather replace the entire rear end with a rebuilt. Ford shop did the tranny work and wasn't too concerned with the rear. Supposedly the ford guy is a really good "gear guy".. Everytime I take it somewhere for an opinion it costs me $$$. I am at a loss as I am not a mechanic myself which is why I am posting for advice here. The whine is there but does not seem at this point to be getting any worse. I just don't want to damage the truck.
Thanks for all your help.

 

Sorry, I meant has the rear end been serviced? When they drop the cover to drain the lube, an examination of the gear pattern, wear characteristics and debris in the bottom of the housing should be noted. If repairs are necessary, you should expect a "specific" list of repairs with a price. Anyone who gives you a diagnosis without doing this is speculating at best. Mechanics who speak in generalities like "loose" and "wasn't too concerned" should be avoided. A shop that specializes in this type of repair (4X4 shop, driveline specialist, etc.) should easily be able to repair your rear end, rather than exchanging the entire rear end. It is also POSSIBLE that a rear end with a slight whine that isn't getting worse could continue service for many miles to come.

 

My own mechanic opened up the rear end 3 months ago and he said the rear end was quite loose. That is when he also found several trans codes in the diagnostic test. He then closed up the rear end as that is not within his comfort level. The truck was towed to the "specialists" at Ford who did the trans repair and test drove the truck. I was without the truck for almost 3 weeks. Despite my asking, that is as far as they got. There are not too many experts around this area which is why I am hesitant again to keep bringing it everywhere. Maybe I should just keep an "ear" to it and see if it gets any worse. Hopefully it won't shred and leave me up a creak.

 

It's good to know that it has new gear lube, since the symptoms may indicate worn gears from a lubrication or overloading problem in the past. A whine that is not progressing will be easy to monitor and will not likely end in a catastrophic failure that leaves you stranded. Eventually, it will probably require a rebuild. If you post up your location, hopefully someone here can suggest a competent shop in your area.

 

Thanks for your advice. I am from southcoast area of Massachusetts.
I guess I will not be too concerned about it for now but will keep in the back of my mind if it gets any worse. Hopefully there are many more miles left in this truck. The rest of the truck seems good. I use it to carry firewood often (natural gas is ridiculously expensive to heat with here in the northeast)
Thanks again. This site is a great resource.

 

If you end up wanting to replace the rear I know just the guy depending on where you live.