Hi:
Did you have the heater core replaced?
To me it sounds like you lost vacuum to the brake booster. The booster is located on the driver's side. The master cylender is attached to it. It will have a larger vacuum line attached to it. Check to see if the hose is still attached. If it is, remove it from the booster to check it for vacuum. (Keep in mind, by removing it, you will create a vacuum leak to the engine, so it may die or run rough until it's replaced.)
If there is no vacuum, follow and inspect the hose for cracks, damage, or if it's disconnected from the engine. Repair or replace as needed.
If there is vacuum, take the vehicle to a shop and have them run a vacuum test on the booster.
If you have any other questions, let me know. I hope this helps.
JOe
Thursday, October 23rd, 2008 AT 3:21 PM