[Morris] Brake problems

[Kevin Wayne Williams]

I have a Spridget disk conversion on my Minor that served me happily for 
     about 30000 miles. Recently, I started to have brake drag problems, 
and decided that the front calipers were shot, because I could not get 
the pistons to retract freely. Replaced the calipers, and all seemed 
well. The truck took a few months off, and I got back in it this week. 
It would run fine for a while, and then the brakes would begin to drag, 
and they were glowing red hot the other night.  Now, all four brakes are 
locked.

Is there some kind of valve in the caliper that I was supposed to have 
disabled? Or is this just a problem with my master cylinder not 
retracting properly?

KWW