How can I determine if I have a limited slip differential? I bought a used 2001 4X4 SuperCrew Lariat Package with a 5.4 motor. Is there anyway to find out ?

 

Look on the door sticker it will have a code for the rear axle. If the code is 2 numbers, 19 for example, it is an open rear. If the cod is a letter and a number, H9 for example, it is a LS rear. Front is always an open diff from Ford.
If the previous owner changed anything, all bets are off.

 

its best to either jack up the rear end and spin the tires by hand and see if they both spin; or trying to do a burnout

chances are the LS may be wasted since most peopel DO NOT take care of them by either neglecting oil changes or putting in fancy candy *** synthetic oils that do nothing for lubricating the clutches

 

Look at the axle code tag on the differential itself. It will say something like 3 55 88LS......which would translate into 3.55 gears 8.8 gears limited slip.
Or...if you do jack up the back end, if the tires spin opposite of each other when turned, its an open diff, if they spin together....its limited slip.

Edit: since its a 5.4....i'd be willing to bet its got 3.73 gears in there....no telling if its LS without checking the tag or the door jamb.

 

Thanks everyone for the quick help. I'll check it tonight.

 

Most likely a 3.55 LS in that 2001.

 

That's what mine had. 01 4x4. 5.4 orp.

 

Thanks again for all the help everyone. The rear differential is slightly leaking and I plant to change the gasket and fluid this weekend. Should I go ahead and change the front at the same time? My truck has 101,000 on the odometer. Also how much gear lube does the front differential hold?

 

It probably wouldn't hurt to change the front. Bear in mind Ford has changed their specs for diff fluid. Used to be 75w90. They now state to use 75w140 and if you have a limited slip to add friction modifier. I am not sure if the weight change is also true for the front. It may be.