Posted by Greg Coffin [67.176.56.44] on Tuesday, August 04, 2015 at 16:14:15 :
In Reply to: Brake boosters posted by Dave in Baltimore [71.166.55.214] on Tuesday, August 04, 2015 at 12:59:33 :
You shouldn't run 2 boosters on a single circuit master cylinder. The master cylinder may have enough volume to run both, but the boosters will not send a balanced return flow to the master when you release the pedal, and it causes problems (dragging brakes, weak brakes, etc). I worked on a 1960's W300 that had a single master feeding dual boosters, and it never braked well, and was dangerous to drive. I yanked the second booster and the system worked fine.
If you are keeping the original style master cylinder just run one booster on it. It will work great. A 251 in decent condition will have plenty of vacuum to run the system.
If you want a true dual circuit, booster brake system, you can buy one of my bracket kits and save yourself a bunch of design work.