Fair question. I know what you're asking but don't know off the top of my head. Will have to use the dipstick and try to guesstimate it. I'm pretty sure it keeps oil al the way out the tubes and not just sitting in the center. I sent Mag an email also to confirm their intent on the oil level. I'll check all that today.

 

Factory fill has a little in the axle rubes IIRC

 

See picture. The lower line is about the bottom of the factory fill hole on the front of the housing (assuming you added fluid just to the bottom of the hole); I do not recall the stock quantity. Note that level takes the fluid juuuuussst barely up to the bottom of the tubes. The top line is 5 quarts (Mag Hytec recommended/intended quantity). This line is my level with 5 quarts which puts it right between the two marks on the Mag Hytec dipstick. Take note that not only are you filling a larger cover with this cover, but now you have 9/16" almost of fluid standing in each tube. This is also by design for Mag Hytec. (*Note...I removed just over 1/2 quart troubleshooting this problem and it barely made a noticeable difference on the dipstick level, but that makes sense since it's so spread out at that level)

See description above and you can see where all that quantity is sitting; but it is a pretty deep cover.
Nope, not a chance.





Both looked completely normal. Nothing excessive that would garner attention.
Nope...zero.

Three days of driving with the new vent tube and no fluid coming out of that. Still a leak by the pinion nut. Which is totally odd...didn't even know it was possible to leak from there. Need to pull the driveshaft and investigate further. Also, just by judging the pinion angle in the garage and compared to either oil level, it would not appear that the front of the pinion shaft would be submerged in oil while sitting static, but not positive.

 

So here's my thoughts, higher fluid level overall, means less room for expansion, and when it does expand it expands even more because there is just simply more there.

Say 3Qts (my recollection of factory fill) VS 5Qts

If it's a 10% expansion turns into 3.3q vs 5.5 that's a considerable jump



If the vent is clogged it's got to go somewhere and the weakest link becomes the leak.

Pinion is spinning 3.55 times faster, generating more friction and heat.

 

Agree with all (except mine is spinning 4.1 times faster, LOL)...except we come full circle back to the fact I've had this quantify in there for 180,000 miles and zero problems until now.

 

I was guessing on the 3.55 but you get the idea

Seals age, vents clog, what can I say?

 

So I think we got it figured out. Have another gearhead buddy at work and I asked him about it today. We drew it out on a piece of paper what that driveshaft flange and pinion nut look like. After drawing it out trying to visualize what the internals look like, it's got to be the pinion seal. The pinion seal seals around the axle housing and I think most of us are accustomed to that outer part going bad and leaking all over the place. Mines not, thus why it's all dry there. But if the internal part of that seal that rides on the pinion gear is bad and leaking, where is that oil going to go?? It's gotta go out the front. The driveshaft flange prevents it from leaking all over the housing like we're accustomed to. So I'm gonna change the pinion seal anyways and see what happens. Gotta be sheer coincidence it just coincided with the oil change. Easy enough job, so we'll see. Still nothing coming out the vent tube after 60 miles again today.

 

Sounds like you have found the resolutions to your problem. Congratulations!

 

Good Luck, it's most likely a major design flaw on 04+ till ??. Many threads online of people complaining of a bearing failing and whining at highway speeds that turns into a all the time whine after intial fluid change.

Here's one for you. 05 changed the factory fill on the 9.75 at 120k miles with royal purple (proper weight) and a tube of MC limited slip. clean brown fluid. inside of diff looks like a virgin.

15k miles later passenger bearing fails, no noise parking shoes smoking.

New national bearings seals on outer axle. No wear on axle shafts. Diff coated in grey slime, gears have knicks all over.

1k miles later rear diff whines terrible. no noticeable pinion slack.

Plenty of same stories on various forums for 04-08s. I can't remember where I bought the MC additive from; amazon, ebay? Was it counterfeit? Was the royal purple to blame? I see countless posts of terrible whining at 60k miles. My advice, if you're a 04 or new 9.75. Don't change the factory fill run till the bearings go.