Simple. Go to the dealer or auto parts store and get 3 quarts (70-140?) gear oil. If you have a Limited Slip Diff. (check your axle code on door jam) then one small bottle of Friction Modifier is required.
Put drain tub under rear diff. cover area.... start loosening cover bolts. I do top to bottom. leave the bolts in... but loose. when all are loose, separate the bottom of the cover from the differential/gasket to let oil begin to drain out. As it gets slower continue loosening lower to top bolts to create more of a gap to let the oil flow out. When oil flow is minimized..... completely take out bolts and remove the cover. TAKE CARE AS NOT TO DAMAGE THE AXLE TAGS ATTACHED TO THE BOLTS. These need to be preserved!!!!!
Clean Differential cover of all old gasket / RTV sealant as well as the diff. surface where the cover will meet. Apply a good bead of new RTV sealant to the clean face of the rear going completely around (a circle) the bolt holes. Let stand till tacky... re-install diff. cover and LIGHTLY install bolts till RTV slightly squeezes out. wait a while... slowly continue to re-tighten bolts... paying attention as not to damage the axle tags as the bolts are finally tightened.... they will want to swing around as the bolt turns and get crimped up.
Just did it the other day... it's easy, but could get a little messy. I used Royal Purple, it already has the friction modifer added in. That link is my video. I'm no superstar mechanic and if I can do it anyone can. Good luck!
Thanks to all of you guys, I pulled the rear cover today and drained my rear diff today. I pulled the spare tire out of the way, it needed a clean up and check anyway.
My diff cover was horrible rusty with 147K. I wire brushed it with a drill attachment after hosing it down with wd40. Cleaned it up with engine cleaner and hot soap water and then brakekleen to dry. I found a permatex rust inhibitor product I had never used in the garage, so I brushed it on and it is setting up in my garage overnight. It claims to provide a good primed surface for painting, guess I will see. I have some black gloss spray on undercarriage type coating to go on it tomorrow.
I bought two small containers of the friction modifier from ford to mix into 3 quarts of valvaline full syn 75-140 gear lube. I do not have a gasket, going to have to find some black rtv type sealer.
The best part today was using the air drive rachet to remove the bolts, feels like cheating. Thanks again for the great info, wish me luck for no leaks,lol.
Thanks Red, the dealer told me 2 bottles of the friction modifier was what I needed. I remember reading here the someone else was having some issues with their LS diff, and it took a 2nd bottle to get their problem cleared up?? I will probably go ahead and put in the 2 bottles in. Any harm with too much friction modifier? And what does the stuff do....why is it so important for the LS diff? I am about to put the cover back on today after getting the black underbody coating stuff to set up. The bolts were a mess of rust, so I primed and painted them with some silver hear paint I had.
Friction modifer makes the clutches slip so you can go around a corner and not chatter or shudder. I suppose to much modifer would just make the lsd not work that well for offroad purposes or something.
I asked both the separate companys I bought my traction locks from and both recommended 1 bottle of ford friction modifier so that's what I been running in my mach I and my truck. The one in the Mach I is different then our trucks but both have been working with out any issues..
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