A4LD sometimes works sometimes not at all

[beans]

88 ford ranger with 2.9 and A4LD 4X4 was working perfectly tell today put it in drive and herd a grinding noise for a second now the forward gears dont work but 1 and 2 work more often than drive and sometimes neutral will be reverse the shift linkage moves normally that i can see toed off the fluid (it was almost 2 quarts low) but topping it off didn't work want to know if anyone had a similar problem and what could fix it someone told me to try changing the fluid and filter but being an old transmission im thinking that might do more harm than good