i have a 99 f350 7.3l 4x4 i need to change the front seal on the rearend i know it takes 75w 140 synthetic gear oil i plan on using the royal purple my question is how many quarts does it hold from being complely empty ive put alot of miles on this truck since i got it and should change it while im down there the tag on the rearend say "3 S 409 E
L73 10 5 9F24"
and if any bodys knows which rearend do i have any help will be appriatied thanks for your time.

 

well i believe its a 3.73 gear ratio rearend but how much fluid do i need to buy that stuff is expensive

 

your best to have 4 for sure and 5 to make sure if you happen to spill when filling .

 

While you are under there, check the breather hose from the rearend. My seal was leaking awhile back and it was because the breather was completely plugged by an insect nest.. The rearend builds up pressure and the front seal is the weak point and it starts leaking..
My manual says 6.9 pints for a 10.5 axle, F250/F350.
If you need a copy of your owners manual.. see:
https://www.flmowner.com/servlet/Con...e&ord=42948682

 

If your going with Royal Purple fluid like I did, get yourself a 5 oz bottle of Motorcraft friction modifier, it's only about 5.00-7.00 dollars, cheap insurance. I had to add about a half bottle because the modifier that was in the RP wasn't enough, I had some tire scuff going around tight turns, half a bottle was all I needed.

 

Also look into the 08+ diff cover. I love mine! I think it holds a little less fluid with that cover because I bought 4 quarts and had a full bottle left after filling. I used RP with no further friction modifier needed.

Here's what it looks like: