HELP, My rear is blowing gear oil out the vent tube

[68rt]

Just finished a total restoration of my 68 B Body with an 8 3/4 323 posi. Whenever I drive the car for about 10 miles it dumps gear oil out of the vent tube on top of the axle housing. The rear was humming and sloppy, thought it may have been a bad rear bearing heating up the fluid and boiling it out the vent. I put in another 323 that I know is good and the car does the same thing. I used NAPA gear oil (80 85 90 weight). The shop manual call for 4 pints of gear oil, but I filled it up to the drain plug as I've done on many mopars with no problem. Could it possibly be over filled? I'm at my wits end with gear oil all over my NOS finish panels. Anyone have some thought on this??

 

[Stumper]

I've had it happen on my dana 60 rear before. First time was after 5-6 laps on a steep banked Nascar track at slow speeds. Just assumed the oil had flowed inward on the banks and came out. Also had it happen after lots of "downtown driving" - lots of turns etc. in hot weather. I filled mine to just under the hole so I could touch it with my finger bent at the joint.. Only other thing I have though of is that mine just has the vent but no hose piece. I've been meaning to try attaching a piece of hose to run up under the frame.

 

[FatJack]

It could be overfilled, take it back down to 4 pints and try it.

Are you using the friction modifier in the diff????

 

[YY1]

I always filled mine to where you could barely feel it with the tip of your finger, if you stuck it in the hole and bent it down- just like Stumper said. A little more shouldn't hurt, but you don't want it pouring out the hole while you're trying to put the plug back in.

 

[67 B-body]

I've filled mine up to the plug hole without issues too.... Don't recall seeing anything coming out the vent hole though.... Hmm,,, how would expanding lube be the cause of this when the vent is clear at the top of the housing? I'm not going out to measure this right now,,, but isn't that like 6" or so from the plug to the top of the housing????
This doesn't add up to me...... I would think the slinging lube from the ring gear would be most likely... Question is, did the vent get messed up at all on the end that protrudes into the housing? I'm not certain, but I thought they were designed with a sort of baffled end to prevent direct slinging of lube from just shooting out.... Also, doesnt the outer portion have a sort of cap on it that just barely moves, spins, twists, wiggles... to help prevent leaking? Are all of these things in tact?

 

[Big Jim]

Got to agree with 67 B-body here- if your vent cap is missing it will make a mess- some of the later vents had a bronze mesh insert under the cap-worked nicely

 

[68rt]

I just pulled a vent cap off an original axle and it is indeed a check valve. If I blow out the vent, you can here a thump as a check valve opening, if I try to inhale the air flow stops. Not sure if this has anything to do with the problem. The one that is currently on the car is a reporduction and I will pull it and compare it to the original. I will first try to lower the fluid level and then see what goes. Thanks for all of your comments and I'll post back in a few days after a road trial.

 

[68rt]

Rear Still Blowing Gear Oil

Well, here's the latest, I removed the axle vent the applied teflon tape to the threads in case to leak was there. I also drained some of the gear oil so the level was about 3/4" below the fill plug hole. I drove the car only 5 miles and it started spitting gear oil out of the vent. Is it possible the oil is foaming???? I have 80/85/90 weight in the case with a posi addative. I'm out of ideas, HELPPPPP!!!!!!!!!!!!!!