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Old 11-02-2011, 08:59 AM
edjack edjack is offline
Officially Welcomed to the 'Fest
Location: San Jose, CA
 
Join Date: May 2007
Posts: 8,784
Mein Auto: '97 540i 6 speed
How does vacuum increase braking pressure?

Vacuum from the engine on one side of the diaphragm in the brake booster (that large tank mounted to the brake master cylinder; you know, the one that fills with water and freezes up in the winter?) allows atmospheric pressure to push on the master cylinder. Nominally 14.7 psi X surface area of the diaphragm, so, for a 6 inch booster, you'd get as much as 418 lbs of boost.

My Shelby GT-350 had 11 inch front disc brakes, and no booster! I had to really stand on them to stop, but they worked great!

Read all about it: http://en.wikipedia.org/wiki/Hydraul...e#Power_brakes
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Ed in San Jose '97 540i 6 speed aspensilber over aubergine leather. Build date 3/97. Golden Gate Chapter BMW CCA Nr 62319.
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