Brake Challenge:

New: Master Cylinder, Calipers, Rear Brake Cylinders/Drums, New Brake Booster, Pads. Only thing not new is the proportioning valve.

Had brakes bled by machine at a shop.

When I start car brake pedal is soft to the point of almost to the floor. Very Squishy. When I put it in gear in the driveway, car stops, but not with confidence.

Within a quarter mile on the road the pedal comes up and brakes are solid. No issues.

I figure if I had a brake booster problem the pedal would be hard, not soft. For the life of me I can't figure out what is causing this problem.
Vacuum?
I read somewhere about adjustment of the rod between booster and master cylinder?
Any guidance would be most appreciated.

Thanks!!

Bill

 

I read up on the Brake Booster Check Valve- It indicates that a bad check valve can introduce air into the master cylinder?? As I understand it the booster assists in driving the rod to the Master Cylinder. I have no idea how it could possibly introduce air into the master cylinder. Very confused

 

The check valve keeps engine vacuum in the booster, it doesn't have anything to do with the master.

Make sure your vacuum line from the engine to the booster is good. On TBI it should run from the back of the throttlebody to the widget and on to the booster. Look for leaks, check for blockages, make sure the check valve grommet seals. Right after you shut the car off, if you pull the check valve out of the booster you should hear a woosh of air. If it doesn't hold vacuum for at least a couple minutes, something is blocked or leaking.

With the vacuum hose disconnected from the booster, the brakes lose most of their authority. It's bad enough that you might not notice you left it disconnected backing out of the driveway, but you'll notice before you get to the end of your street. The loud sucking vacuum leak is pretty easy to hear when it's left open, but a leak could be small enough that it'd be hard to hear.