1948 chevy 1/2 ton
with my '48
I had this problem and it was the ring gear was worn out... my cheapskate brother told me of how you could simply turn the ring gear around (with slight modifications) and we did and it worked perfect...
I had to heat the flywheel in my wife's oven (might suggest an option to that) but it was hard to get back on but heat did the trick... no more loud grinding noise every other time...