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So I crawled under the old girl today to look at the rear end. It still has the tag on it and as best as I could read it the tag is stamped " S319D 3 309 5L27 "
I'm sketchy on the latter part. I didn't clean it terribly well but the first line of "S319D" is positive.
Two questions: From what I've found this appears to be a limited slip, correct?
Secondly, can I get a new seal and drop the face off it? It's leaking and since I'm not having any mechanical issues I'd just like to replace the u-joints and seal up my leak.
If you want to pull it apart, you have to pull the axles. That means pulling the rear wheels, brake drums, brake parts if they are in the way, 4 bolt flanges, and then a slide puller to pull the axles. You can put the brake drum on backwards, put the lug nuts on even with the studs, and then grab the drum and use it like a slide hammer to get the axle out.
Be positive it's leaking. If there is a drip, take that in your finger and smell it. It should be stinky gear oil. You would be surprised how many times it looks like your rearend is leaking, but really it's something up front on the engine, transmission, power steering, etc. A small drip up there will blow to the rear and hit the rearend, gather up, and drip off the bottom of it.
Also check the nut that holds the pinion in place. It if works loose, then it will wobble and cause the pinion seal to leak. It happens.
Look at the attached PDFs, sounds like the placement of your "L" is in the date code and not gear ratio code; I have never actually seen your tag so I have to make some assumptions.
The first shows how to decode the tag, sounds like yours is the lower one built "from 10/84".
The second, scrolling down to the S319-D entry tells you it's a 3.50 ratio.
#1 make sure the vent is clear. If the pinion seal is leaking it can be replaced without pulling the rear end. And if it is a 9" the pinion housing can be removed without pulling the rear end (there are shims and an o ring seal to keep track of.