Help my axle housing vent tube is blowing grar oil out!

[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 (5 pints). I've filled it to this point 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?? I also have a new repro vent tube on the axle

 

[snakeoil24]

Let me understand your manual says 4 Pints and you filled it with 5? What don't I get here?

 

[65 Plymouth Satellite 426]

Yepper...You Overfilled It!

 

[440roadrunner]

Let me understand your manual says 4 Pints and you filled it with 5? What don't I get here?

Yepper...You Overfilled It!

I have news. The several Mopars I owned, with 8 3/4 in 4 of 'em, and later a Dana in one of those, plus a Dana factory under my sixpack RR, were all run "to the bottom of the filler plug" I'd hazard a guess that most service station jockeys did the same thing. I NEVER had a problem blowing oil out

Here's the chart out of the 67 manual, and below that from the 72 manual. You can see some minor changes were made, but the 8 3/4 in 72 can indeed be run "to the bottom" of the filler hole:

 

[Stumper]

You're better off going by level measured to the hole than volume. Depending on your differential (or spool?) the volume needs can be quite different.

 

[daredevil]

Something wrong. Did you add the sure grip friction modifier.If not my bet is youre frying the clutches.

 

[Cranky]

The lack of friction modifier shouldn't have any effect on frying clutches etc. It's mainly to help reduce chatter especially when turning. I would check to make sure you're not overfilled first. And if you have a bearing getting hot enough to make the fluid boil, you would most likely have a bearing that's frozen up.

 

[67 B-body]

I remember a thread on this topic a year or so ago...... If memory serves, the OP found that the vent design was different than another type in another 8.75 housing. One had a different method of baffling "shielding" the vent insert..
Anyhow,,, long story short, I believe changing out the vent insert fixed his problems...

 

[Cranky]

This is what should be on it.....

http://www.ebay.com/itm/1940s-1950s...Parts_Accessories&hash=item5d34ba53fa&vxp=mtr

And it should be holding this onto the axle tube...

http://www.ebay.com/itm/Mopar-A-B-B...Parts_Accessories&hash=item5ae95f5885&vxp=mtr

 

[daredevil]

The lack of friction modifier shouldn't have any effect on frying clutches etc. It's mainly to help reduce chatter especially when turning. I would check to make sure you're not overfilled first. And if you have a bearing getting hot enough to make the fluid boil, you would most likely have a bearing that's frozen up.

Then tell me whats happening when they chatter. Clutches arent slipping freely and you have unwanted friction. Friction builds heat.

 

[RustyRatRod]

I run the office at a transmission shop. We do transmissions, drivelines and differentials everyday. Everyday. Every differential we do has a measured amount to fill according to MotorAlldata. If the book says 4 pints and you put in 5.......here's your sign.

Just for the sake of arguement, I will say this. We've seen bad bearings and differential clutches generate heat and overheat the fluid and make it puke out the vent.

Also another culprit that'll do it......although not a concern with our cars........all wheel drive vehicles will exhibit the same thing if some dummy puts different size tires on front and rear. The viscous coupling will struggle and MAKE the axle with smaller tires try to slow down and compensate......and overheat it and puke the fluid out. It will eventually burn the viscous coupling out......but not before the differential. lol

 

[440roadrunner]

different size tires l

Heck that would do it right there. They don't even have to be different tires. Maybe you get a mismatched pair of rear wheels, one a little wider than the other, this causes one tire to be smaller.

AND you don't want to check the typical "shade tree" with the rear jacked way up and the front down low. Car needs to be level!!

 

[Cranky]

Then tell me whats happening when they chatter. Clutches arent slipping freely and you have unwanted friction. Friction builds heat.

Never had them chatter just driving down the road but going around a corner....heck yeah but I've never had a rear end puke fluid just because of no friction modifier when everything else was right.

I run the office at a transmission shop. We do transmissions, drivelines and differentials everyday. Everyday. Every differential we do has a measured amount to fill according to MotorAlldata. If the book says 4 pints and you put in 5.......here's your sign.

Just for the sake of arguement, I will say this. We've seen bad bearings and differential clutches generate heat and overheat the fluid and make it puke out the vent.

Also another culprit that'll do it......although not a concern with our cars........all wheel drive vehicles will exhibit the same thing if some dummy puts different size tires on front and rear. The viscous coupling will struggle and MAKE the axle with smaller tires try to slow down and compensate......and overheat it and puke the fluid out. It will eventually burn the viscous coupling out......but not before the differential. lol

The biggest heat generator in a rear end are the ring and pinion and bearings contribute their fair share too. I've also diagnosed cars with different/mismatched tires on the rear. Even that didn't make it puke fluid. It's kinda hard to diagnose someone's car from behind a keyboard but imho, since he's a pint over, I'd look at that first.

Heck that would do it right there. They don't even have to be different tires. Maybe you get a mismatched pair of rear wheels, one a little wider than the other, this causes one tire to be smaller.

AND you don't want to check the typical "shade tree" with the rear jacked way up and the front down low. Car needs to be level!!

Best way to check a tire to be sure they are the same is to measure the 'rollout'. I like to use a flexible tape measure for that but a steel tape measure can be used if you are careful with it.
http://www.mickeythompsontires.com/tech.php?bulletin=s8

 

[70redbee]

Has anyone noticed this thread is a year old? Took me a while.