Front and Rear Differential Fluid Change?

[Piraya33]

I need to change the fluids in my front and rear diffs mainly because the rear is leaking right now. I have been doing some searching and I have found that I should be using 75w140 gear oil but I am wondering which one would be the best. I have no idea what rear diff I have or if it has a limited slip because the idiot that owned the truck before me replaced the rear diff cover with an aftermarket aluminum one and didn't bother to put the tags back on. Anyways, I was just wondering what you guys use and if there was anything I need to watch out for while I am changing them. This will be my first time performing this task, so any info at all is greatly appreciated. Thanks everyone!

Also, can those of you that choose other in the poll above please post your recommendation? Thanks!

[Highbeam]

I use mobile 1 synthetic for both front and rear. Different weights are required. Whether you have LS or not, the mobile 1 is all you need. No additive is required.

[Tony V]

Royal purple is good stuff. its 75w14o in the rear and like 75w90 or something in the front...

[cpayne6335]

I change the diff, trans, t-case every 6 months, so I just get the cheapest oil I can get. Now if I did it once every few years, ya, maybe I can see spending extra cash. I am in and out of my truck all day and night. Long trips, short trips, stop and go, pull trailers. I like to inspect the gears and look for wear. I am due for my fluid changes, but strapped for funds, just got 2 hub bearings, and need to get a few seals while I have it apart.... so I get to put it off for another month

[Piraya33]

Anybody else? I am gonna change them this weekend. Thanks!

[2005F250]

I think the rear gets synthetic with a bottle of friction modifier and the front gets regular non synthetic gear oil.

[wingnut]

other...Mobil1

Originally Posted by 2005F250

I think the rear gets synthetic with a bottle of friction modifier and the front gets regular non synthetic gear oil.

agreed...except that the synthetics NORMALLY have the modifier in them already

[bottomsup]

Other. Im using redline because I have summit racing in my town...

[chrispaine]

I think I'm going to go with Amsoil when I do mine..soon. And I think he was right when he said you dont need the Friction modifier with the good Synthetics.

[balistic]

I use royal purple in front rear and transfer, no complaints, don't know if any is better than the other.