1990 928 S4
After DEVEK Days 2000 driving event at Thunderhills Park, I decided to get the brakes up to snuff. With the help of Marc and Brad at DEVEK, I replaced the brake lines, pads, and fluids. I also replaced one sensor, installed a 33 bar bias valve, and swapped the right and left front rotors (installed backwards by PO). After extensive bleeding, the brakes still felt a little mushy. After checking for any leaks in the system, Marc checked the vacuum check valve located below the brake fluid resevior and said it was not working at 100%. They didn't have any in stock, so I ordered one, and installed it later.
The packaged contained the check valve and some vacuum line. I didn't need all the extra stuff, just the check valve. The installation was pretty straight forward. I removed the drivers side air tube, disconnected the four vacuum lines, pulled out the old check valve and the install the new check valve.
It costs about $29 and took about 10 mins. to install. The main point is when everything else on the brake system is working properly, a $29 check valve will make the brakes seem mushy and soft. The new valve made an amazing difference. The brakes are now firm and very controllable.
Copyright 2001, George A Suennen