Differential fluid change

[DoobieBrother]

Ok, I know these trucks (`68) generally use 90 weight gear lube. Couple of questions, though.

• How many of you guys are running synthetic.
• If I did go synthetic, could there be any issues given that I have a hunch that if the fluid has ever been changed, it was LONG ago?
• Are you guys replacing with a gasket on the cover, or are you just using some sealer?
• Favorite sealer?

[Longhorn Man]

You'll have no issues at all going to synthetic other than the cost. That oil will be good dang near forever as long as it does not get contaminated.
I use sealer, the Right Stuff is awsome, but expensive. I get it for free, same with the oils, so I use them.

[cdowns]

i always like to wash out the insides with kerosene (windex spray bottle) when changing out really old fluid in the rear. i always change to synthetic(mostly royal purple) i just go with the original type gasket held in place with permatex aviation form a gasket// the good thing with royal purple if your running posi is you dont need the posi additive// i run royal purple in my trannies also

[Longhorn Man]

brake clean is another goos solvent to clean the rear end out with, it evaporates, leaves no film, and comes in arasol cans.

[BCOWANWHEELS]

wash out diff with starting fluid, it cuts the old oil great, has pressure behind it, i use castrol senthetic 85w140 and seal it up with permatex ultra black silicone. jmo
bob

[Texasdeere]

I like to run synthetic in the drivetrain, especially the rear end. Synthetic is good stuff but cost too much to use in the engine for me.

[DoobieBrother]

Ok. Thanks for the info guys. Should be gett'n after it this weekend.