Hi, I have a 2004 f-150 4x2 XLT supercab.
I have noticed while making turns there is a bad shaking sound coming from the back tires. The sound only comes when I turn. I've had some opinions such as I should change my rear differential fluid. Any help would be greatly appreciated

 

i would change your rear diff fluid. you need 3qrts of 75-140, and a tube of friction modifier. that fixed mine.

 

try the oil with modifier first, but it sounds as if the diff clutch packs are going

 

Ok. Thanks for the help, I have obviously never done that. Is this something I can change myself. ?

 

yes very simple but messy process. Just let the rtv set up for a good hour before adding the fluid back in. Or buy a gasket makes the process painless. They can get pricey tho $25 or so. But well worth it. Being you have never done it I would get a gasket. RTV can cause issues if you mess up then it can leak a lot.

 

Like others have said just a fluid change will fix it unless you let it go for awhile. The friction modifier has problably lost its effectivness. Mine has done the same and changing the oil solved the issue. I used rtv and have never had an issue. Fyi, i used ford modifier and lucas 75-140w synthetic. You will need three quarts.

 

Yes you can do it yourself. It will be a mess though, but not quite as big of one as dropping the tranny pan. If you have the limited slip rear end, it it almost 100% the issue. I would add the friction modifier first, if that takes care of it change the fluid later with another thing of friction modifer. do a google search on changing rear diff. oil for your truck.

 

It seems any vehicle with al LSD has issues with carrier failure.
If your tuck has an LSD (Check first) you can try the additive, but you may have damaged spider gears, bearings crown pinion. You may want to have it inspected, sounds like a rebuild is in order.

 

I disagree with the diff faillure at this point although valid, these clutch packs are picky in cold weather or extreme heat. They need the right lubricity and if the fluid is breaking down they will grab instead of slip especially in slow type turns while accelerating say from a stop for example.

 

Well that Is exactly when I get the worst sound a shaky vibrating sound when I'm turning from a stop.