I have a 2001 Durango 5.9 R/T. December 2011 I started having brake issues. The pedal became very soft. I bled thebrakes with no success. Then discovered the master cylinder was bad. Since then, the master cyclinder has been replaced, both rear wheel cylinders and a front driver side brake line. I have taken it to proffessional mechanic twice to have it checked. Both times they bleed the brakes and the pedal gets stiffer. But, over the period of about two to three months it gets softer again. I have checked the system for leaks and cannot find any.

Yesterday I pulled off the wheel to look again. The rear shoes are worn to the metal almost and the front appear barely touched. I replaced all the brakes at the same time in February of 2011.

I am at a loss and looking for any suggestion. Thanks