mine doesnt grind going into reverse
try holding in the clutch for 5 seconds and then putting it in reverse. i know my old cherokee had this problem. if you went to put it in reverse immediately it would grind but if i held the clutch in for 5 seconds and then put it in reverse it was fine.
or push the clutch in, put it in first, and then put it in reverse w/out letting the clutch out in between. this works well too. i think it has something to do w/ the input shaft still spinning when you push the clutch in.