What's up guys. Sorry I took me too long to get back to you regarding this issue. Well, I finally found the formula to overcome the problem!! my truck used to make weird noises and would vibrate really bad everytime I turned left or right while taking off. The problem started when the guys at the shop recommended a differential fluid change on my 99 f-150. They not only added the wrong type of oil, but di not added any type of friction modifier. To tell you the truth, I didn't know a friction modifier was needed. The problem started becoming more noticeable as I drove my truck during the winter. I rapidly knew that something was wrong with the differential and some people told me that my clutch packs were just worn out. I decided to go for the cheapest (oil change with friction modifier) before replacing the clutch packs. The owner's manual said that my LS differential uses 75w140 Synthetic oil plus some frinction modifier. I go the synthetic oil form the dealer and they recommended a synthetic friction modifier as well without checking in te computer. I thought they were right since one assumes those guys have a lot of experince (shame on them!), they were wrong. The problem didn't solve until a more experinced person (from the same dealership) gave me the right convination: 75w140 synthetic oil plus non-synthetic friction modifier XL3. This is a weird convination since one expects to use synthetic friction modifier with syntheic oil. anyway. The explanation to this was that ford changed its formula and now they have to be combined in this fashion. Belive me, it worked for me! I thought my truck had some permanent damage since I drove it like that for almost six months. Fortunately, nothing bad happend which demonstrates that ford trucks are really built tough! j/k. Well, if you haven't solve your problem I really encourage you to do waht I did. It worked just fine, and know my truck drives nice and smoothly. I do recommend to remove the pan (cover) and not just drain the oil so that you get rid of all the old stuf completely. I hope this helps you!!!

 

Thanks for letting us know what fixed it