I just had my differential and rear axle bearings replaced in my 67 coupe - non sure grip- the only problem was a bad pinion bearing , had I known this I would not have had the rear bearings replaced. My car also sat for a very long time (20 + years) the spline that inserts into the drive shaft going into the differential seemed to have slack or play in it, in both the bad differential and the one with which it was replaced. If you have a bad part in your differential do not panic and buy another - these things can be overhauled and re-installed. I held onto my old one and will have the pinion bearing replaced which will make it good as new. Marc '67 Coupe