Brake problems

[Todd Young]

Car = 1993 Audi 90S (fwd)

I had the rear brakes replaced by an independent shop (that I trust) and 
I replaced the front brakes. That included discs, calipers, and pads all 
the way around.

Here's the problem. Something is "sticking" and not allowing one brake 
circuit to "release" properly. The braking in my car is divided into two 
main circuits, RightFront-LeftRear and LeftFront-RightRear. I sometimes 
here the RightFront pads dragging slightly, and I've had problems with 
the LeftRear sticking considerably after using the hand brake. Now since 
the hydraulic system is what adjusts the hand brake mechanism, and with 
hearing the front right pads dragging slightly, I figure there must be 
some check valve sticking somewhere.

I know there is some sort of check valve in the master cylinder that 
prevents the pads from backing off completely when the pedal is 
released, as disc brakes rely on a minute amount of pressure to keep the 
pads slightly rubbing on the discs.

I've tried bleeding the system, and I took the RightFront caliper off 
the disc, placed a piece of wood in between, extended the pistons and 
then compressed them back, in an attempt to "back pressure" the system 
to insure there was no major blockage in the master cylinder.

I still have issues with the one circuit. This is most evident by the 
activation of the ABS at really slow speeds. I figure the ABS is kicking 
in because the pads have just a little too much pressure against the 
discs and it is causing an impending lockup so the ABS kicks in.

My opinion is that there is something worn/wrong in the master cylinder. 
The only other option is the ABS controller, because I've checked the 
lines and they all look good, plus I've bleed the system and there are 
no problems there. My gut says that since the ABS works, just too much 
when going slow, that the ABS controller is probably fine and my problem 
lies in the master cylinder, which I should replace.

Input? Am I on the right track or way off base?

Thanks for any help.
-- 
Todd Young
7079 Dawn Ave. E.
Inver Grove Heights, MN 55076