Thanks to all for your helpful advice. As soon as the truck got home I took it apart underneath. Oil was clearly coming down from the bottom of the yoke from under the flange or dust cover thingy. I loosened the nut, took off the yoke and could see the seal was damaged underneath. The rubber lip where it is bonded to the metal outer part of the red seal was pushed away.
Thankfully I had my stock yoke yet and had chose to not try to use it thinking that there may be a warp involved when the drive shaft sheared itself loose (probably one of the u joint straps sheared away first). I was able to visually compare the oem yoke with the Dorman one and then pulled the damaged seal to test fit it. Even though the seal deformed slightly when coming out of the housing, I could see that the seal was too tight of a fit over the Dorman hub.
I had purchased another seal (National 2034) to be ready for this. I could use the new seal to test fit it over the Dorman part and over the old stock one. You could see that the fit was perfect on the stock one and was too tight on the Dorman one. I don't have a digital micrometer but it has to be 1mm difference if that. But since the fit is too tight on the Dorman then the idea is that when I used light taps and slow tightening of the center nut to seat the new Dorman hub in the seal that it was too tight and tore part of the rubber away creating the leak.
Prior to the truck getting to me I had spent at least an hour online with part numbers, comparing measurements listed online, and searching RockAuto, various online sellers, GM oem sellers, ebay, etc. I could not find a measurement discrepancy and even the 'oem' GM pages were pointing me to a yoke with a hub size that was going to be a fuzz too big. Also on the 'oem' GM pages and the Dorman page the dust shield looked bigger than my original stock one.
Since I had the stock one and the dry fit test with the new seal was perfect, I took the easy way out and installed the seal and put the original yoke back on (with a new washer and nut, using the new U joint straps and 4 bolts) Was very careful to get seal perfectly in place and added mounting lube. I smoothed the mating surface of the old yoke hub with light 3M red wool sanding pad. It went back together just fine. The dust shield is smaller but this is the way it was in the factory.
So, a test drive around the neighborhood, no leaks!! Will watch it over night. Hosed down the underside with brake cleaner to try to clean up some of the spattered oil. Confirmed the breathing tube is open and tied up in a safe place. Wow, how fortunate if all I needed to do was use the original yoke and a new seal and have this problem solved!!
How can i tell what axle series I have? The parts look up indicate that most of these yokes are for AAM or 3R part type but is that telling me the size of the U joint disks or the rear axle size? I couldn't find any stamps on the axle itself.
RShrimp, you were correct that if I couldn't use my original yoke I may have had to go to a junk yard to get the correct one. I think after seeing the difference between the yoke mating surface that there is one maker on RockAuto that has the same 'design' as my oem one.
You can see in this picture taken from the GM look up page using part 12470387 that the all the GM part numbers that I could cross reference (and the Dorman) which SAY they work for 1995 have like a double lip on the part that goes in the seal. See red arrows in my picture. That 'outside' lip might be what holds the metal dust shield on? But it seems to add a fraction of thickness as well (or isn't really meant for a 1995) It also ships with the 'wrong' seal for my application.
The oem one has a smooth hub that fits in the seal as in the 2nd picture. The Richmond brand pictures show the smooth surface one and a smaller dust ring that exactly matches the size of the housing that it mates with behind it on the diff. I guess if I had a micrometer I could measure the Dorman one vs the Richmond one but warning to anyone with my axle or yoke type that the Dorman WILL NOT WORK. Without both in hand I would not have been able to figure it out (although the brand new but ripped seal was the important clue)
Thanks to all again and hopefully this is the last update. If this post helps anyone, cheers!
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