It's been going on for a few months now. I haven't been driving it much lately, so I don't think about it, but, especially when its cold, I get this howl or a whine in the rear end. I replaced everything brake related back there about 5 months ago, so I don't think it's brakes. I haven't had the time, or more importantly the money to mess with it, but with winters bad roads and having to plow some snow, I'm gonna have to nip it in the bud. what's most likely at 285000? Bearings? Ujoints? I have no vibration whatsoever. It rolls 95MPH as smooth as silk. just the howl. any ideas??

 

It could be pinion/ring gear backlash. Or low on gear lube.

 

When was the last service done on the rear diff ?

 

Does it come and go with acceleration? Get louder or quieter? Or, is the noise constant at all speeds?

 

last lube change about 100k ago. No difference under acceleration or deceleration, or coasting in neutral. After jacking it up (and putting it on jackstands) I ran it in gear, and put a metal pipe against various spots on the rearend to try to narrow it down. There might be slight metal sound coming from the diff. But nothing bad I don't think. I'm still gonna do a fluid change today to see if there's any odd wear in there. I did notice a slight wobble or looseness in the right wheel, so I pulled that apart. The axle nut was actually a bit loose. It probably would have been fine if I had just tightened it up, but, since it was apart and I had to go buy the tool anyway I replaced the bearings. That didn't help at all. So, Fluid check and change today, and I guess I'll go from there.

 

Go with a synthetic lube and 4oz of the friction modifier.Napa sells the FM now.

 

Check the bottle of whatever gear lube you go with, alot of the synthetics have the modifier already in them.

 

Mine did that around 120k.... just kinda started to happen, drove the same, got louder and louder. It was sometime after a diff fluid change, used the right fluid and Ford modifier. Not that it's related. But I eventually ended up having to do a full rebuild (ouch on the wallet).

 

Well here's the update. I did the fluid change. Used royal purple and added only 3oz of modifier. All seems good with that. Did it fix my noise? It helped a little bit, but, No. So now I've swapped the bearings on one side of the rearend and changed the fluid. $250 in the hole so far. So then I notice noise in the drivers rear brakes. That rotor for whatever reason in the only brake component I didn't change back in August. It looks rough, so I replaced that $58 more. Yet a little more quiet, but.... Still the howl. I start looking at u joints, figuring that at 285k, surely they have to be about done. Nope, all are solid. So, last thing the center support bearing. Just moving it around by hand it felt fine, but I decide to pull it out to check it anyway. It was toast. seemed solid when in place and moving the driveshaft up and down, but once it was loose, it wobbled all over the place. $28 for a new one and 20 minutes later..... Drumroll.........No Howl!!!! quiet as all get out. What a relief!! I had the whole "rebuild" thing in my head and was really sweating it. As a side note, with all that I did, the guy that works for me is pissed. He drives a Tundra and spent $800 on parts and 16 hours just doing the bearings and seals. God bless American ingenuity. $336 and did twice an many projects in under 8 hours!!

 

glad you got to the bottom of it, lock that into your memory bank just because you dont feel slack in a bearing surface dont mean that the bearing isnt dryed up from grease or going out, good job

 

Glad you fixed it.Thanks for posting back!