Brake problem

[RicebalLDR@aol.com]

        Hi I have a 1991 200TQW 20v that has developed a problem with the 
brakes not releasing (all four wheels) while driving. They seem to work OK at 
first but then start to mess up with normal driving and brake application. 
The brake petal has less and less top play as this happens. A vibration 
develops as well. I have no warning lights and the ABS works normally. The 
brake petal seems to return to it's normal position after the petal is 
pushed. Its almost like the pressure is not releasing after brake 
application. Because of the high cost items that make up the system I would 
like to trouble shoot rather then just R&R components. Any thoughts?      
Thanks and Happy Holidays  Richard Friedrich