As the search for a smaller booster that didn't whack on the air horns on the triple Webers got stupider and stupider I finally ordered a $43 7" dual diaphragm hot rod booster with the wrong bolt patterns and had a go. It took 2 hours to make the adapters, the car runs fine, but the jury's out on max braking effort until I rebuild the front calipers and free up the one sticky piston. I'm assuming the vacuum from 1 Weber manifold is enough. If you're OK with non-BMW parts and some diddling, it's maybe an option. Caveat Emptor.
The American booster-to-firewall bolt spacing is too big for the E9, so that has to come down...and the MC/booster spacing is also too big, so same. I used 1/4" aluminum. The reach from the booster/MC needs diddling as the MC has that protruding piston which won't go into the new booster. The drive pin in the booster output is a 6mm bolt with a locknut, so you'll need a longer bolt to match the spacer. And the pedal/booster linkage is 1 1/4" too short. The shaft diameters are both 10MM but have different thread pitches. I welded 2 appropriately threaded nuts together with a little spacer between.
The American booster-to-firewall bolt spacing is too big for the E9, so that has to come down...and the MC/booster spacing is also too big, so same. I used 1/4" aluminum. The reach from the booster/MC needs diddling as the MC has that protruding piston which won't go into the new booster. The drive pin in the booster output is a 6mm bolt with a locknut, so you'll need a longer bolt to match the spacer. And the pedal/booster linkage is 1 1/4" too short. The shaft diameters are both 10MM but have different thread pitches. I welded 2 appropriately threaded nuts together with a little spacer between.
