Issue for the hive:
I recently purchased a 2006 F150 KR 4x4 with 80,000 on the clock. It has a 6" lift and 35"x12.5"x20" tires. This is my first lifted truck so when I got on the highway it was loud and a little rough driving down the highway; I chalked it up to the big mud tires, they have descent tread left, maybe another 20k left.

Roughly 10-20 miles down the highway at 70mph all of a sudden everything goes quiet...smooth, no more "road noise". It caught me so off guard that I almost pulled over because I thought the engine just completely shut down. Actually, everything appeared normal and it was actually a very quiet and enjoyable ride from then on. This issue happens every time I get on the freeway, which isn't often.

I almost feel as if the tires, driveshaft, engine, something may be a little out of balance and then all of sudden whatever the issue is it finally finds its steady state.

Background on the truck:
- I have not had the tires balance and rotated since purchasing the truck 1 month ago.
- It does have a fairly loud tick that correlates directly with the accelerator.
- I dropped the transmission pan and replaced filter and cleaned magnet which was covered in a metallic sludge. The transmission fluid had a hint of burning smell to it and the the bobber was still in the pan making me think it was the first fluid drop and replace. Issue was happening before and after transmission fluid swap.
-The steering wheel has a slight vibration in it while traveling in a straight line but the vibration is still there before and after driving on the highway when everything goes quiet.

Any thoughts fellas? I appreciate it.

 

Can you pinpoint where the vibration is coming from? If you can you can try rotating the tires to test if it's those.

 

I haven't been able to pin point the cause for either the vibration or noise. If I were guessing, I'd assume the vibration is from the tires but not the noise. I'm thinking they may be dependent of each other but wanted to put all of my known information out there in case someone would be able to piece it all together.

I'm going to open up the rear differential, clean it up, and replace the fluids. I'm wondering if the groan or howling I hear for the first 10 minutes on the interstate is caused by the gears.

 

I replaced the rear differential fluid late last night and I haven't had a chance to take her on the highway to get the speed up yet but the fluid was pretty nasty and it appeared to have a fair amount of very fine metal shavings.

Replaced the fluid with Royal Purple 75W-140 w/ 4oz of a Friction Additive.

One thing I did note and I'm unsure if this is normal, but when I took the fill plug off (first step) there was quite a lot of fluid which poured out of the fill hole. The truck was pretty level when I did the change and I wasn't expecting anything to come out of the fill port.

Is that normal?

 

lifted trucks have their diff/rear ends pointed upwarded. Pinion bearings don't get enough lube because of it, so guys will over fill the diff's to help with this problem. lifted trucks will always have pinion bearing go bad because of a lack of lube. May also want to make sure drive shaft move in and out of trans w/o getting stuck.

 

Rev, thanks for the info.

As for the drive shaft, should it be able to slide in and out by hand or would I need to articulate the trucks suspension to verify it?

 

If a 1 pc drive shaft, would have to unbolt it, and see if it slides freely in and out of trans/transfer case. If not, lube the inside of the splines. w/ a 2 pc. shaft unbolt from diff. and see if it slides inside the black rubber boot, if take apart and lube it. cut one metal band,lube . reinstall w/ zip tie!