How exactly is this done? What weight Oil and how much of it? Is a new differential cover gasket needed? Any liquid sealant also? Synthetic oil ok? Limited slip additive needed? (heard that somewhere)

How long of a job is this?

 

Gasket should be under 5 dollars. I would buy sealant too.
Just take out the bolts, and then you will probably have to pry the cover off. Put the cover back on with the new gasket and then start filling it up. I put Royal Purple 75w90 in mine. Its sythnetic and I have no problems with it.

 

Seems easy, I'll pick up some Mobil 1 or Valvoline and the gasket at work. Would 80W 90 be ok?

How do you drain it, just let it pour out when you take the cover off or is there a drainer plug or anything?

 

DON'T PUT SYNTHETIC GEAR OIL INTO A CONE CLUTCH POSI UNIT!

It will slip.

Just use regular gear oil and YES YOU DO have to first add a little full bottle of GM Limited-Slip Additive then add the gear oil to the hole level.

 

Well ok, no synthetic. The Valvoline i'm pretty is conventional oil. How much of the gear oil do I need? 1 or 2 quarts?
I assume I need to get the Limited slip additive from GM? By the way, I dont have a Posi... Do I still need it?

 

About two quarts if dry.

And no you don't need it if you do not have a limited slip (a.k.a. posi) rear diff.. Open diffs do not need any additive since they have no clutches. Opens "CAN" also use synthetic oil.

 

Thanks for the help man. I'd run out there and start doing it now..but its night

 

Here, I tech you wahtto look for when you are in there so you will learn how to remove your axles if you ever need to in the future.

This is an Auburn posi (or limited slip, same damn thing ) But even on an open you can spin it around til you find this bolt head. Its a holding bolt for the diff pin that keeps the axles spread apart inthe diff which in turn hold the C-clips from falling out.

Remove it (bottom half of picture)

 

Then you can tap the diff pin out.

After it is completely out (removal shown on top picture)

You can then push one axle inward at a time and remove the C-clip. Then simple pull the axle out the side of the car. Note in the picture I am using a magnetic antenna to ease the process of grabbing the c-clips.

 

Also, you might not want to take those axleshafts out just for fun. The tiny little lockbolt (in the second picture above) likes to snap!! The head snaps right off and leaves the threads in the differential. The case of the axle wraps up around that- so there's no way to drill the bolt out. (That's why Dean used a wrench and not a socket; you can't get a straight-on shot at that bolt.)

Happened to me in a few junkyards already (trying to get 30 spline axles), and happened to my own axle- I couldn't get the threaded part of the bolt out so I had to put a junkyard axle on. Some people used picks to rotate the snapped bolt... I tried, but couldn't get it to move.

 

Very good warning Tom. Thats why I said if you "need to" for any reason take the axles out, but I should have included that very improtant point that they do snap off very easily.

I had one snap on me years back also- what a mess. It was in there so long it froze. I actually turn mine every single time I am in there (about once a year- its a quick twist loose and resnug) just to keep it free from seizing from heat and pressure. But I put it into there new so I would not advise that of anyone on one that hasn't been touched in over 10 years. They do not need to be forcefully tight, just a good snug- yet the heat and pressure will seize them over time if they are never touched.

 

How do you drain it, just let it pour out when you take the cover off or is there a drainer plug or anything?

 

You got it, just pull the cover. And try not to get the old slimy eggsmeeling gear oil on you (got that one Tom, I remember that discussion )

In a perfect world there could be a drain hole, but the factory does not provide for this on anything GM's college boys engineer. Take in account the glorious 700r4 fluid pan, oh what a wonderful day we are having with ths one, its called get every g(od dman spare rags you own for that project on a stock tranny pan.

 

How much do I tighten the differential cover bolts? Just until they are snug and a few turns around?

 

tighten them down to 20ft-lbs. That is the spec if i remember correctly. Check your haynes manual because i am not certian on it

 

LOL! Yeah I can't stand the smell of gear oil; yick. Good idea about giving that bolt a spin every year- when I get my 3.73/posi/disc axle going again, I'll have to do that. (Gotta buy a new posi for it) Any idea if they sell that lock bolt "new"?

Also when you tighten the bolts, of course, use a "star" pattern just like your lugnuts so the gasket seats evenly. I think the gasket is a FelPro TOS-18663... but my skills aren't up to date Heck, look a few messages above, I realized I typed "30 spline axle"... no such thing for our cars. I guess I meant "28 spline" instead