I've got an 89 GXL NA, and whenever i get to about 50 miles an hour the rear axle starts to vibrate. Driveshaft already replaced. How can I tell if I need new inner CV Joints, outer CV Joints (not replaceable) or complete axle assemblies? Who has the best price for these components?

 

If I remember correctly I only paid about $55n a side for rebuilt assemblies. It's not that tough to replace them.

 

Are you sure the vibration is in the axles? Check you tire balance; it usually goes out after a few thousand miles, and if you bumped into anything that can also change the balance. It could also be in the driveshaft, so check the u-joints.