(1995 Ford F150 XL 4.9L I-6 Manual Trans 186,000mi)

I'm going to change the rear differential fluid and replace the cover. The code from the tag on the cover reads S832J, 3188. I've found a cover with the 10-bolt configuration that matches my old cover. Also got a gasket as well.

Question is do I need to put something on the gasket or on the cover to help it adhere? Like silicone or something? Or just slap it up there dry and tighten the bolts in the star pattern?

Last question - I got Valvoline 80w90 oil and it says "Limited Slip" on the bottle, but it has "Limited Slip" on ALL the bottles it seems. Still okay to use this in my non-limited slip fire-breathing butt-kicking Ford?

Thanks in advance for any tips!

 

For the Gasket i would just clean the edge of the diff to get all of the old gasket material off of it so it gets a nice clean seal and just put the seal that the diff cover came with on it. For the Diff Fluid, some of the sites that i read say that LS diff fluid may cause a shorter life of the diff due to the Friction material inside the oil. I would return the LS oil and find a NLS oil.

 

I keep reading from various posts across the web that it won't hurt the non-limited slip differential by using the gear oil with the additive in it. Anyone else have any input on this?

 

I wouldn't think it would being that it doesn't hurt the gears in a limited slip diff but it's not a bad idea to get non ls fluid if you don't have ls.

 

I'd use Permatex The Right Stuff on the cover then put the gasket on that. When you next change the oil the gasket will stay on the cover and can be reused. Also a dab of Right Stuff at each bolt. Use the Valvoline you bought that's great gear oil, people are over thinking it having LS additive in it. Good time to check condition of the differential vent tube.

 

Limited slip fluid in a non-LS won't hurt a thing. Its like wearing a belt when you already have suspenders. Unnecessary but harmless. As far as the gasket. Unless it has a molded O-ring like the MHT cover, I use no gasket at all. Clean both surfaces thoroughly and apply a 1/8" bead of Permatex Ultra Black, encircling the bolt holes. I've never tried Right Stuff but will have to look into it. The one down side of Ultra Black is future clean-up. It really sticks.

 

I can't remember where but I've seen tests that showed the ls friction modifier in gear lube actually gives is better performance on a non ls type diff. And on the gasket issue don't even use it just use a good bead of permatex and give it an hour or so before adding gear lube. With just using permatex it'll still seal up good if the cover isn't good and flat whereas it won't with a cork gasket.

 

One time using Right Stuff you'll throw out what you've got left of any other product. It comes in a cheese wiz type can and is pricey but one can lasts a long time. Always ready for immediate service after install.

 

Excellent advice, fellows. Appreciate it all.

 

Closing thoughts on changing the rear differential fluid & cover+gasket:

-Bought a $7 fluid transfer pump from Walmart which made adding the fluid so much easier. I later used this same transfer pump to fill my manual transmission. Well worth the $7 bucks

-Excellent tip someone provided by making sure I could remove the filler plug on the back of the diff before removing the cover and draining. Had I removed the cover and drained the fluid and done all that work, I would have been sunk had that fill plug got damaged or couldn't be removed

-Latex gloves came in handy. That old diff fluid is the most foul, most putrid-smelling stuff I've ever encountered. Glad I had a box of latex gloves to keep from getting that crap on my hands

-After changing the rear diff fluid, I changed out my manual transmission fluid. I don't know if it's just me, but since changing the rear diff & trans fluid, the truck seems to roll easier (especially up hill), has more power (again, uphill), shifts much easier, and I swear it runs cooler. I drove today for over an hour in 90+ degree Texas summer heat and the needle never got off the letter "N" on the word "NORMAL". Usually gets up to and stays between the "O" and "R". Will fluid changes make the engine run cooler???