Fluid in quarts needed for my rear differential

[Ben_Greenberg]

Hey guys,
Im looking to replace the gasket and fluid for my 78 GMC C15 heavy half with the 12 bolt cover. I just want to make sure I dont overfill.

The manual I have lists every option and im not sure which one ive got.

Thanks everybody!

[bake74]

     I think I understand your question. 
     The fill plug on a 12 bolt is toward the top, fill it till fluid comes out when your truck is on a level surface.  Put the plug in and your done.

[Ben_Greenberg]

     I think I understand your question. 
     The fill plug on a 12 bolt is toward the top, fill it till fluid comes out when your truck is on a level surface.  Put the plug in and your done.

Thanks for the quick response, I was hoping to figure out how many quarts I needed to buy. I have 3 but I don't want to be left without enough fluid while working on it.

[bake74]

      Well the manual does not say exactly how much it takes, though when I did mine I believe I had 4 quarts on hand and used just short of 4.  To be on the safe side you could always buy 2 more and return 1 if you did not use it.

[Ben_Greenberg]

Sounds like a plan. Thanks for the advice!