ok its my brothers 2003 F-150 2X2 4.2L....when he would turn left or right from a stop or slower speeds it would vibrate and rattle in the rear. so i asked my buddies dad ( who knows his stuff) and he said to put the rear end lubricant in there . i did, got better but not much, than i took it to a place they said it was the " limited slip, CLUTCH PACKS. wanted 350.00 for them plus 350.00 to fix, i bought them for 60.00 off ebay and had them put in..ok so now the vibrating is GONE feels great when you take turns or everything. but NOW when he lets off the gas it sounds and feels like a clicking. i asked the guy who worked on it and he said i put em in right its just that u let that problem go soo long that it might have burnt the differential and he said that its like new clutch packs rubbing up against an old burnt differential. and that it might need a new one, he pured 2 bottles of that rear lubricant in the diff. and said to drive around for 2 more weeks and if it didnt get better to bring it back.. u guys know ur stuff here so im asking if anyone knows what to do or has any advice.? thanks soo much guys.. the truck has 80,000 on it too.. jus to let u know

 

The factory limited slips arent all that great to begin with. If it were me Id leave it alone and just let the clutches wear out. If you really need a limited slip toss your old differential and get a nice aftermarket setup.

 

if i let it wear out then wont it start vibrating again when i turn?/

 

Put FORD friction modifier in... it really makes a difference... My truck and my fathers truck both did that and we changed the rear lube for Royal Purple and put friction modifier in and it went away..

 

I dont think so but maybe someone else on here knows for sure. Maybe try the drivetrain forum. My older trucks have worn out limited slips and they just act like regular open diffs right now. I believe those were traclock differentials. If it were me Id rather spend the money and get a detroit truetrac differential.

 

read my opening statement (burnstoughford) i said i put that modifier in there, the guy put two bottles of it in there. it still knocks letting off the gas....i dont know what to do..

 

read my statement... change rear end lube then put friction modifier in...its only a suggestions... take it or leave it

 

BTW... i might be wrong but i think the guy you had put your clutch packs in migh tbe wrong.... i think that the clutch packs are the differential... have you ever thought about having a second opinion...?

Have you checked to see if the berings have gone bad?

 

you guys are my second opinions, dont take anything i say the wrong way..im not mad, ill take anything u guys say...i appreciate it...this guy emptied to fluid tice, took the clutches back out and did em again, same thing, it has gotten a little bit quieter than when i first took it home but it still is a problem..

 

Was there any metal in the diffs either time? Where the clutch packs new that you put in...

Im not sure but i dont understand how the clutch packs are different from the differential.. i thought they where the differential? Anybody?

 

the differantial is the gears in the back i gues it all looks like a bunch of teeth.. im no expert obviously by what i call these thigns but the clutches are more like spacers that go in between the gears i gues. i saw it all but cant explain.. i know teeth in a mouth just not car things..

 

the "differential" is the angle set of gears. you have a pinion sticking out the front toward the drive shaft and a ring gear (8.8, 9.75 inch dia, etc) that runs off the pinion. there are 2 or 4 small gears that connect the left hand shaft to the right hand shaft. this allows one side to turn faster than the other when you turn a corner. the LS clutch mounts on ones side and also connects the two shafts together. it allows them to turn maybe 10% different in speed so you can turn a corner, but will not let one spin while the other is stationary, like being stuck in the mud. the clutch will grab when the speed varies by more that 10% (lets say). the friction modifier just lubes up the plates of the clutch and makes sure they dont grab too easy. lets the spped difference between the two side be a littel more, (lets say 20%). thats what the clutch, and the differential do.

 

so what do u think is wrong if its makes noise as i let off the gas?? the vibration went away when I turn but now the guy is saying i might neeed a new differantial??/