Hi, I recentely bought a 97 f150 4x4 stepside off my dad. He just changed the differential fluid and used lucac 80w-90. I was reading this on this fourm and came across people using 75w-90. Is this good for the rear and is it affecting anything? Thank you for your time,
Mark

 

My 2000 F150 rearend calls for 75W140 full synthetic. Do a search, I'm sure there's more info out there for you.

 

If the 80w-90 is in the front end that's fine, if its in the rear end that's not the correct weight of gear lube that Ford recommends. All F150s take synthetic 75w-140 in the rear end. Learned this lesson the hard way myself. 30K ago I wanted to change the lube in my rear diff, I crawled under there and saw the tag saying 75w-90 and that's what I bought and put in there. Then I had the bright idea to actually look in the owner's manual and do some research on this site and found that Ford no longer recommends 75w-90 in the rear end due to complaints of noise and vibration. The heavier lube helps cut down on this. I've run the 90 weight for the last 30K and am fixing to change it out, this time I will use the 140 weight. Ironically, the last few weeks I have noticed increased noise and a slight vibration from the rear end. Hopefully, the new fluid (and a tire rotation) will fix the problem and its not a bad u-joint or something more serious.

 

On a 1997 F150 4x4, it's 75w140 in the rear (syn) and 75w90 up front. I got some Royal Purple for $9.50/qt and plan on changing my diff lube out soon.

It'll be it's second lube change that I've done on it... I used Amsoil the first go around.... Seemed fine, but have always heard good things on the RP and it was about $3/qt cheaper.....

MItch