Join Date: Dec 2005
Location: The Swamp...Lousy-anna
2006 Blue over Primer'd Bondo FPR 6spd #23424 slapped together 2/22/06
Regarding the extra capacity of the larger rear end covers that Mike In Az sells, when I used to pull my Airstream with the stock rear-end cover (and fresh gear oil) after a long pull up a big climb in the Smokies (when it wasn't even that hot out) my rear end spit fluid out of the top vent tube. It wasn't over-full.
The dealer replaced the cover and the fluid when I got home (only partly because it was a rusty mess even when new). Next trip, it did it again. It used to groan and whine on big climbs out west...I even posted here years ago in the middle of a trip thinking the rear was about to go out. Thankfully it didn't, but it didn't sound happy going up climbs pulling a trailer.
Then, (years ago now) I bought one of Mike's finned extra capacity aluminum covers. It is filled just below the port on the housing. I haven't had a concern of any sort since. No spitting fluid, no whine, no noise, no ANYTHING. And it looks cool too.
I consider that a difference-maker.
BTW...remember that when filling, if you have the back of the truck raised to get under it to fill it, when you lower it back down you will be over-full if you filled it when the rear was raised to just where the fluid drips out. Make sure you compensate for that.