I had this exact problem and fixed it last week. Before anything else, the first thing you need to do is change the fluids in the differential, since it's the cheapest and easiest option at first. I have an '04 FX4 supercrew. 3.73 gears, 52k miles.

I took the diff. cover off, and cleaned it until it would damn near show my reflection on the inside and flanges. I used an entire can of parts cleaner to clean the differential out. The gears looked perfect, no chips or missing teeth.

I wiped out the diff. as best I could to get the parts cleaner out, and used some of the RVT stuff and replaced the cover, then added 2 bottles of limited slip additive from the dealership (8 oz) Then I filled it with 2-2/3 qts of Amsoil synthetic differential fluid.

After about a day of driving around, the vibration disappeared. The next step if that doesn't fix it, is to have the clutch packs replaced. That was about $350 to have it done around here, including the cost of the clutches.

 

are you sure its not your boss or wife chewing on your rear end

 

Yeah , didn't think of that..

 

HI!... Well if you don't get it takin care of soon you end up with this STERLING 9.75 mess :

 

 

Neal, that looks nice! whats that mod called? J/k

What caused that amount of heat/destruction? A burnout or wheeling or something? Weirdest thing I have seen was in my fathers '89 silverado, never abuse, towed a light fishing boat at most, we were heading down a residential road near home and he went to turn the corner and somehow the crosspin busted and the part that wasn't secured by the crosspin bolt slid out and wedged between the carrier and diff case. what a mess that was!

Best we could figure is that is had some sort of crack or defect in it and finally after 175,000 miles decided to give up.

Buy anyhow, back on topic, I would at least pull the diff cover and do a fluid change, its relatively cheap and will allow a visual on the parts that could be causing the grinding feeling.

 

ok guys, thanks for all the info, tommorrow (saturday) im going to the ford dealership to get the auto tranny fluid for my 03 boss, along with the additive that was stated, is there anything else i need or any tricks i should know about. this is my first tranny experience so any help would be appreciated.. im also going to clean it out, should i use brake cleaner, or what. give me the exact name and ill get it... thanks for all the help

 

I couldn't agree more. Does the phrase "...Those aren't two pillows!" ring a bell? LOLLLL

P.S. ZVR: Did you ever take any pics of how your grille lights are mounted?

SL

 

Hadn't heard that one in a long time.

 

Arrrgh! No, I keep forgetting. They're screwed into the frames of the lights through the surroundingsectinos of grille, but I'll snap some pics and try to get them up next time I have my camera handy.

 

I have an '05 that did that -- i caught it before 36k luckily and the dealer fixed it, It was in fact a limited slip problem