Hi everyone I was hoping someone could help me out with this issue. So I recently installed a new brake booster as well as a master cylinder on my 1984 Mercedes 300d. However when I start the car I can hear it hiss especially after turning it off, the brake eventually get hard and I can't turn off the car. I can't seem to figure out what I am doing wrong when it comes to installation. This is the 3rd brake booster I have bought because I thought the first two I put on were defective. If anyone can chime in and tell me what it could be? I even put a new o ring between the cylinder and brake booster yet still leaking.


I know the vacuum pump works because when I plug off the line and use my mityvac it reads over 20hg. Any ideas