Sticky Brakes (Brakes Not Fully Releasing)

[Marc Boucher]

I've been having intermittent problems with the brakes not fully releasing.  The best Audi shop in the city (recommended on this list) has missed it twice, so I thought I'd see what insights you guys might have.

There doesn't seem to be a pattern to it.  I might take a drive and on the way, it starts not-releasing fully as I take off from red lights.  Then I might get where I'm going, park the car for a few hours, and on the return its perfectly fine.

Car is an Audi 100, 1990, non-quatro, not-turbo I5.  

Shortly after the problem first occurred, the 'brake wear' light indicator also came on.  So I took it into the Audi garage, told them of the problem.  They changed the front pads, but said that everything else about the brakes seemed fine.  

The car wasn't driven for a few months, and when I started driving it again, the problem came back.  Took it in a second time last week explaining the same problem.  This time their diagnosis was that the rear guide pins had seized, the rear pads were rusted, and the handbrake had a seized adjuster.  All of these were repaired, replaced, or adjusted as required.

On the drive home from the mechanic last Friday, I noticed that the brakes started dragging, just as before.  Being Friday at 6pm I couldn't take it directly back to the mechanic or park it in rush-hour traffic, so I hobbled home with it (another 3-4 miles).  By the time it got home, the brakes were smoking.  The FRONT brakes, only.  The rims were too hot to touch.  The rear might have been a bit warm also, but I can't say if more so than usual.

Something else to note.  I could hear something directly in front of me in the engine compartment.  Essentially coming from somewhere in the Master Cylinder area.  I don't mean to suggest the Master Cylinder.  I could also say, coming from the hydraulic assist reservoir.   Just saying the sound was coming from 'that area'.   The sound was both mechanical and hydraulic.  Here's what I mean:

Imagine you're stopped at a light and the brakes are sticking.   You take your foot off the brake and the car doesn't move because the idle doesn't overcome the slightly stuck brakes.  Then you hear something sounding like a liquid suddenly released to flow through a tube or hose, immediately followed by something mechanical, i.e. a piece of metal moving or a valve opening, and at that same moment the brake frees itself.

Tomorrow the car is back at the mechanic.  Not meaning to second guess them, but since this is their third try, I'd like to perhaps suggest a few things to check based on the wisdom of this list.   Given this description, any ideas on what the most likely causes might be? 

Thanks for any ideas,

MC