The rear wheel bearings on a C4 Corvette are fairly complex pieces of mechanical engineering. There is an inner flange that mounts to the suspension knuckle. There is an outer flange that the wheels bolt to. Between the two flanges is a pair of sealed bearings surrounding a splined cylinder that the outer end of the half shaft mates to. When these guys start to wear, several things that you don't want to be involved with start to occur. First the car starts to get a bit twitchy. It's not real bad, the car tends to wander in the lane and under power the tail seems to move about a bit. This is all happening because the rear wheel geometry is in a constant state of change and the rear wheels are driving the car in random directions. As the problem progresses, tire wear becomes an issue and we all know how expensive it can be to put new rubber on one of these cars. Finally, if left unattended long enough, the bearing will fail and you will be paying a towing charge to complement whatever other expenses you incur.
The better avenue is to check these bearings while you are performing routine maintenance. With the rear of the vehicle raised, apply pressure to the top and the bottom of the tire and attempt to rock it on its axle. You should find that there is no movement, if there is movement in excess of a few thousandths, it's time to do some serious checking. Start listening carefully, if you are hearing a popping noise when making tight turns, the car is acting twitchy under acceleration, showing signs of uneven rear tire wear, or needs constant correction while cruising down the highway, it's time to get those bearings changed before you're in real trouble.
The change-out process for a C4 Corvette is not a simple screw driver and pair of pliers type of project. Of course it's not rocket science either, so it is a quite doable home garage project if you prepare for it properly. When you see what a professional shop gets (up to $800 for the bearings and several hundred more for the labor) to do this job, you'll want to turn the wrenches yourself if you can. OEM (i.e. genuine General Motors) rear hub and bearing assemblies sell for around $250 each through Chevrolet dealership parts departments and Corvette parts and accessories marketeers; aftermarket replacements can run $80 to $90 less per unit. A huge part of the advance planning involves having the right tools on hand when you start the process. Two of the things you may not have in your box that you surely will need are a #36 metric socket and a #55 Torx bit; the rest of the hand tools are pretty common fare.
This procedure will take several hours to perform. But, if the rear wheel bearings are in bad condition, the car is dangerous to drive and the bearings need to be changed for safety reasons. Besides that, worn bearings make C4s handle poorly and imprecisely, and what's the point of having a Corvette if it's going to handle like an ordinary car? And, by doing it yourself, you can save close to a thousand dollars. So now that we have the new parts and all of the tools rounded up, let's get on with the show.
When we originally looked this project over we thought that we could use an impact driver to loosen the #55 Torx bolts. As it turned out there was not enough room to get a good clean swing at the driver. All was not lost, we were able to get enough of a whack at it to firmly seat the bit into the head of the bolt and eliminate the possibility that it might slip out and tear up the bolt. From left to right we have the impact driver, a 36mm socket, an impact extension, and a #55 Torx bit.