Small Engines (Lawn Mowers, etc.): lawnmower will not stop, disc assembly, brake disc

Question
    I have a mtd (husky 18.5, 46 inch cut riding mower)(model   
13AS608H131) and the mower will go in reverse and forward but will not stop.  I have replaced the front drive belt with a 90.5 inch belt which is what it calls for and the rear drive belt is 754-0468.  I can take off the rear drive belt and the front drive belt will stop like it is supposed to.  I can give it gas and it does fine with rear belt off, but when I put the rear drive belt back on the wheels will still run and it will not stop.  I hope you can help because I have done a lot of work on this mower for me to hit a tree to stop.  The brakes does not seem to stop it either but when you release the gas pedal it should stop.  CAN YOU HELP?

Answer
Have you checked the brake pad?  Is it wore?  Is the brake disc assembly dirty and rusted causing it not to work correctly?

I would start by examining the brake disc assembly.  They frequently rust and bind causing the brakes not to works.  You may have to remove and clean the assemlby with a wirebrush.
Let me know what you find.
Eric