Rear Diff Gear Oil Level Rise?

Guys,

I have been battling an annoying pinion seal leak on my 8-3/4 489 for sometime. I topped it off last year by pulling the plug and just filling until the oil was at the bottom of the plug.

Since then I always get the drips when I drive and park it. Past few months I noticed that the oil was coming out of the axle vent a bit and the pinion seemed to leak even with the car just sitting.

I wanted to make sure I hadn't leaked out too much, so I went to pull the plug to top her off and gear oil just pours out of the plug. I probably lost a good 3/4 cup or so before the level dropped to the bottom of the plug.

How would this happen? I checked the oil this time in the exact same spot (in my garage) that I topped it off last year. The excessive oil might explain why the pinion is leaking but how would it rise so much????

Any ideas?

Driven through any high water lately??

Just a guess but the first thing that comes to mind.. The oil would sit on top of the water and "rise"...

No never. This car never sees even rain.

Finally someone with the same problem I have and have had for 12 years.... it perpetually over flows

I worked in service station as a kid out of high school, the old time mechanics would warn me to never fill a differintial to the plug level when cold, we would fill it so it was about a inch down from the plug cold. I have service many vechicles with hot engine oils, rear ends and trannys, all of them would dump rear end lube out when hot
My message is don't fill it up cold I use a thin small screwdriver or something similar to check the fluid levels now, I use to use my pinkie finger but that gets old wiping the goo off of your fingers

What Cab said, pull the plug & let it flow out to the bottom of the plug when hot. should be good

If it happens after doing that, your vent is probably plugged.

This makes sense. The odd thing is that while I did top it off cold, I also checked it this time while it was cold as well. It was a hot day but the car hadn't been driven in several days...

Since there was some oil coming from the axle vent, I am guessing it can't be too clogged. The little crimped cap on it moves around freely.

Had a similar episode recently. Filled the diff on a project 'till it was running out of the fill hole and put the plug back in.

For a while after, I had a pinion seal leak. After it leaked down awhile, it stopped. I figure the diff self adjusted.

Was the axle level when you filled it?

I had an 01 Chevy PU I purchased new.. ( miss that truck) When doing the first service on it the rear fluid was supposed to be 1 inch below the fill plug, per the service manual... Thought this was odd, but it makes sense after reading this post....

Most gearboxes used to be set up that way. The proper oil level is found when you put your little finger through the hole and reach down by bending the first joint. Proper oil level is when the oil just barely touches.

Yup it can be messy and I hope you can get your finger out! No idea why the gear manufacturers set it up like that.

R.

Yep I was taught in high school auto shop in 1973 to always fill rear ends and manual trans to about a 1/2" below the plug. Up to the rear end plug actually has to much oil run out in the axle tubes and gets at the axle seals. Even bearings that get the diff lube get plenty when filled 1/2" below the plug hole. I remember my shop teacher saying if you fill it to run out the plug hole its to high as it will raise even more when the fluid gets hot. Ron