There is a little check ball just above the armature in the solenoid. What happens is metal in suspension in the oil gets pulled into the center of the coil of the solenoid. After all it is a magnet. Eventualy enough metal builds up around the armature inside the coil and it binds the armature causing it not to release the check ball which vents the lockup shuttle valve. I have actually taken the solenoids apart, cleaned the armature and coil and reassmebled them. They are still working to this day and this was 5 years ago on one transmission.[/QUOTE
I found no metal in mine, my plastic spool collapsed onto the armature.
I drilled the hole larger and solved the problem.
In the 85, it happened after nearly 100k miles.
In my 87 it happened after 12k miles but within a few years of the 85 problem
demonstrating the problem was not mileage related.
You have to break a weld to get it apart but you can assemble it back onto the trans
without re-welding it.