The master cylinder, booster, lines and wheel cylinders are all new and I have a check valve in the vacuum line to the booster. I had to bleed the brakes several times to get all air out. I also bench bled the master cylinder before I installed it. I drove the car home 8 miles from the upholstery shop with good pedal and brakes on Saturday. Yesterday I pulled it out of the garage. No brakes. Master cylinder is empty. I now thnk thats why I had to bleed the brakes so many times. The fluid is going somewhere and when I step on the pedal I put more air in the system. The wheel cylinders are not leaking.
Bad master cylinder? If so am I filling the booster with

 

I had that happen one time-the fliud was going into the booster.The rear seal in the Master was defective. ---bil

 

Sounds like I need to remove the booster and drain it. I hope the brake fluid does not damage the air seal in the booster.
Thanks.

 

If that is happening , the booster is bad. And unfortunately new parts fail, especially now a days.

 

The Booster shouldn't be bad if it's only been a very short while, it's the rear seal in the Master Cyl. that's probably the culprit....

 

X2 on this, Common problem with cars that set a lot. You can rebuild the master cylinder with a kit and a cylinder hone, very simple task.