I have only recently begun to do anything with my vehicles beyond putting gas in it, driving it, checking the oil, tire pressure, and fluids. So you'll have to forgive me if I sound/am ignorant.

I have a 1994 Ford F-150xl V8 5.0. I know that the last time the differential fluid was checked it was noted to have a leak but was filled. I am sure that it needs to be filled (as that was a while ago). My question is: should I go ahead and change the fluid in it (as it seems fairly similar to an oil change which I can do) or just put more into it? And where do I find out the recommended oil for it? I looked in my owner's manual and here online and I could not find it.

 

To change the differential oil you need to remove the differential cover. There is no drain plug. Be sure to have the gasket already. The recommended lubricant is hypoid gear lubricant. You will also have to add a friction modifier for limited slip differentials.

 

Black RTV is appropriate for sealing the diff cover. Thats what the factory uses.

 

I was wondering why I sometimes couldn't find a gasket for certain vehicles.
Lucky for me I use black RTV for everything.

 

You can just add fluid to it, the plug is the fill mark, just fill it till it starts running out. Also just a side note, I have heard of shops using a suction device and a small hose to empty a dif without having to open it up. Pulling the cover isn't hard and it gives you a chance to clean any junk out of the bottem. I would check the manual or call the dealer for the exact fulid. Anyone know how often your recomended to change dif fluid?

 

your supposed to 80w-90 gear oil i used vavoline when i did it a few weeks back and seems to work well

 

how do I know if my differential is limited slip and in need of a friction modifier? and if it does, any particular kind/brand?

 

and how accurate is this:

http://www.fordf150.net/howto/differentialfluid.php

I already looked in the owner's manual and didn't see anything about the differential at all. Would it be under something else? Should I get a Haynes or go look at one for that information?

 

it is in the very back in the maintance tables

 

Owners manuals don't say much about anything. I like Haynes manuals, I own one for every vehicle I have owned. The recommended oil I stated was listed in the Haynes, no specific weight listed. There is a tag bolted to the differential that has the gear ratio on it and would also have an "L" on the tag to signify limited slip. The "L" designation is something I picked up here on this site so any additional information on that would need to be from whoever listed that info in the first place, I can't remember who. I have never had a limited slip so I can't recommend a particular brand. That link looks like a pretty good generalization of the process.