1987 A4ld 3-4 shift solenoid

[tmar04]

I have 87 B2 w/a4ld and no 3-4 shift (no OD) lockup in 3rd works fine. all other gears and shift points right on the money. changed fluid and filter, no help.this model does not have the electric, or electronic 3-4 shift solenoid. what makes it shift? what am i looking for when I drop the pan? someone please educate me. I see lots of posts about the 88 and up trannys, but not much info on earlier models. thanks to all.