My question is: How do I get the old fluid out?

Remove the rear cover?

Drill and tap a hole for a plug in the cover?

Messy any way you try.

 

 

 

The more difficult way is to remove the housing cover, which is a bunch of work from what I've read.

 

I have also seen a post somewhere about very carefully drilling a hole in the bottom of the differential and tapping it to accept a drain plug.  I would imagine this would be much easier to do with the differential removed, or at least open.

 

When refilling it put the GM posi-lube in first and then fill the rest of the way with gear oil.

 

Since I've been considering my options for about a year I'll throw a few things out there to consider:

- As I recall, its necessary to remove the rear spring and endlinks to gain access to the differential cover (you would probably be wise to consider replacing the rear spring and hardware, you wouldn't want to break anything and send the tires up into the fiberglass)

- Shocks are probably shot too!

- Getting the spring bolts and differential bolts out could be tough.

- But, If anything is gooped up or disintegrating, you'll never know just by siphoning out the old fluid.

- Siphoning will never clean anything that might have gummed up, nor will it remove any water that may have gotten inside.

- Eventually, you may end up replacing seals or bearings anyway.

- Check the rubber bushings where the beam that supports the differential is mounted, they are probably shot.  If you're into the project far enough (or paid for the labor to get this far) to open the rear diff cover you might as well change the mounts.

- Come to think of it, the bushings in your suspension strut rods may be gone as well.  Might as well do those too!

 

Bottom line, this is definitely a corvette tip-of-the-iceberg issue.  The rear end can easily turn into a complete rebuild issue.  The labor involved to get far enough to open the diff up to take a look is enough that you may be at that point where it's foolish not to do the entire job.  Of course that's not to say that you might not be able to get by for the time that you own the car just by changing the fluid.  But, consider that you'll never have the peace of mind in knowing that the rear end is in good shape and that you'll probably end up replacing 75% of the bushings and rear spring and shocks anyway.  Corvette rear ends are complicated compared to regular passenger/muscle cars and there are more parts involved that need to be in good condition for the car to keep driving right.  Granted not everyone has the spare cash lying around to rebuild the entire rear end, but it's worth thinking about where you want to go with the car in the long run.

 

Just my 2 cents though.  Like I said, I've had a lot of time to think about this.

   

 

Thanks all for the advice!

This pump is also useful for brake bleeding and to check manifold and carb vaccuum. 

The local Corvette shop says that they change the diff. oil twice in order to get more dirt and gunk out. Does this make sense?

 

I'm looking ahead to springtime and would like to change the fluid in mine then.

 

I planned on using the turkey baster method with some hose on the end. That Vacuum pump that 71Shark mentioned sounds like a good bet.

This pump is also useful for brake bleeding and to check manifold and carb vaccuum. 

 

LOLOL......dummy me...I own one of those.......and never thought of it!!!!!!!!!

 

Thanks!!