Hello,
I'm doing some pre-winter maintenance this weekend. I want to replace the rear diff oil and gasket. I plan in using Mobil 75W-90 synthetic gear oil. My question is how many quarts do I need? Saw some you tube vids on an older Silverado and he used not quite 3.

Thanks,
Tom

 

They're right. Some diffs take a little over a quart and a half. Other diffs take a little over 2 quarts. No matter what diff you have... Fill up to just under the filler hole and insure that your dif vent is clear and unobstructed

 

Mine took just under 3. I had 4 ounces left over in the last in the last bottle.
Side note: PB Blaster is your friend.

 

When I did fluid swaps on my truck, the front diff, rear diff and transfer case all received fluid until it just started to overflow. Be sure to remove the old gasket completely, scrapping off any remnants or crusted debris for a proper seal.