I've got a '97 4.6L, auto, with a 3.55 non-LS diff and tow a trailer about 4000 miles a year that is at the top end of my tow capacity. The truck has 95K miles on it about 50/50 highway (country roads) and city driving. I've got conflicting information on changing or not to change the diff fluid.

Do I or should I change the diff fluid as part of a 100K preventative maintenance action or should I just leave it alone? Is there a gasket (factory CD manual doesn't show one) you can use to seal the cover or just use RTV? Do I need to use friction modifier on non-LS diff?

I am changing the serpentine belt, tensioner, radiator hoses, radiator flush, trans flush (every 36K or so), trans filter, injector cleaning, plugs, wires, and possibly new coil packs. Should I do anything else?

Thanks for your help.

 

Change it......not that tough. Here is a good write-up to help you (for a jeep, but will work the same):
http://www.stu-offroad.com/misc/diff-1.htm

Use the RTV.

 

My Uncle has worked on Trannies all his Life....I was doing Tranny Service (He was actually doing the work) And I asked about Diff.....He asked what the problem was, I said None, and He said Exactly Just leave it.....But I guess if you trailer hard, it may be worth it....Doesn't hurt to open it and look at it and decide from there.......And No, I never did change mine.....I only have 104K on it. An older guy towed a 25' cmper with it twice a year, to and from the camp site and it seems alright, although my tranny fluid was slightly burnt.....

 

It can't really hurt...if anything, it will give you a heads up as to the condition of the diff...there's no gasket...just use RTV. As far s opening it and deciding from there, once you open it, you're changing it....cause there's no drain...just remove the rear cover...refill to the bottom of the fill hole on the front...

 

Just a quick tip about getting oil into the rear end......
If you remove the ABS sensor out of the top of the housing it is much easier to fill the diff through there rather than through the plug on the side.

 

Look for metal tags on the cover bolts. I just changed mine for good measure and the tags said 75W140 SNYHT ONLY. No big deal except the Snyht oil is a lot more $$$ than regular gear lube. Mine did not have a gasket but I bought one and used it with some sealer. Mine is a 1998 3.55 Non LS F150 2WD 4.6L 118,000 Miles. I did not have any trouble nor do I want any. Changing oil is never a bad thing. I may have spent a little money I didn't need to but I may have saved a big expence later too. I'm going to drive this truck a long way.