i have a2005 f-150 5.4 it has 144k miles i would like to change the rear end lube. it has limided slip , what type of lub do i use and do i have to put a additave in?

 

Use 75w140 full synthetic. You will need a friction modifier if you have a limited slip diff. Look at your axle code on the door sticker. If it is letter and number, example B6, it is limited slip. If it is 2 numbers, example 19, it is an open diff and no modifier is needed. Capacities are in your owners manual. If you do not have an OM, you can download one from www.motorcraftservice.com for free from the owners manual section.

Note - your OM may say use 75w90, but Ford has since changed the specs to 75w140.

 

Royal Purple 75w140 already has the friction modifier in it - just a heads up.

 

Good luck to you.... I have 80 K on mine just did the diff fluid front and rear last weekend... After changing it heard a noise minutes later...
Trucks still apart as the rearend needs to be overhauled... All new bearing etc...

 

Yeah... might as well do the outside bearings and seals if you're in there. Quintin has a pretty good write up in the "Technical Articles" section. If you don't do it now, you'll be spending another $40 to $50 on new rear end fluid when you decide to do it later (unless you recapture the fluid).