DISCLAIMER: I have sidepipes, if you have a rear exiting exhaust, this may still work with additional ratchet extensions and a swivel.

No need to remove anything other than the drain plug. I did this on the floor in my driveway without even jacking up the car. The key is a 8 point, yes, 8 point 5/8 socket to get the drain plug off. I have a '79 and I'm making the assumption all C3s are 5/8 but better to verify before running out and buying the socket. I got mine from a local tool distributor for $15, but I'm sure they are available online too. This socket is designed to remove square plugs. With this socket, there's enough room to swing a ratchet with an extension. To drain the diff, I used a "topsider" oil suction tool. A topsider is used to suck engine oil out of the dipstick instead of draining from the pan (merits of either method can be debated in another thread). Once I had the old oil out, I used a cheapie HF liquid transfer pump to fill 'er up. One side of the pump in the container of new oil and the other in the diff. When half the first quart was in, I poured the additive into the container, gave it a shake and continued the fill. The whole quart was in the diff with about 6 pumps. It took slightly less than two quarts plus the additive to fill. Total time invested was maybe 25 mins and the majority of that was sucking thick oil out thru a tube small enough to fit in a dipstick tube. Probably could have used the liquid transfer pump the other way to get the oil out faster. But my point here is that I didn't have to remove the tire carrier or even jack the car up. Good luck with your projects.


This is all I used. The Topsider wasn't necessary.

8 point socket is key

5/8 for '79.

 

I found a 5/8 open end crowfoot on Amazon to do this job with. I forget exactly how much it was, but it wasn't expensive.

I already had a set of those, but in the more usual flare style..