I have heard of a sudden failure scenario. The car suddenly fails to engage any forward gears, or slips really bad when trying to go forward, but reverse is just fine. This is the dreaded B2 piston failure that can occur on early 80s trannys. It can be prevented by installing the improved piston used in later models. I suspect a lot of bad trannies could have been put back in service with this $100 part.

I had shifting problems with my 84SD when I got it. When warmed up it would suddenly slip when upshifting and end up between gears. Forward motion would stop and the trans would free wheel a bit then suddenly kick in. Cleaning a clogged pressure line to the Alda, adjusting the bowden, and exercising the modulator with a Mityvac a few times and the problem went away.

Jerry