# brake booster vs. master cylinder



## Galimba1 (Aug 16, 2002)

I have a dumb question:
what is a brake booster? 

Is the brake master cylinder the big black thingie between the firewall and proportioning valve? 

Am I talking about the same part?


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## bahearn (Jul 15, 2002)

The brake booster is usually a vacuum diaphragm in a large drum-like thingy. The booster is sandwiched between the master cylinder and the firewall. Proportioning valves are usually integral with the master cylinder. Older cars might have external proportioning valves; those cars I owned with that "feature" had them bolted to the firewall. Brake lines ran from the master cylinder to the proportioning valve and then to each corner of the car.


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