How do vacuum-assisted brakes work on a car with forced induction?

 

IIRC there is a 1 way check valve in the tube going from the I.M. to the booster. Blocks out boost lets vacuum be pulled. im not sure its called a check valve but it is something like that.

 

There's a vacuum reservoir. Well, not a reservoir per se, just stored vacuum in the booster. Your engine is pulling a vacuum just like an n/a car unless you're romping on it. The booster stores vacuum (unless there's a leak in the system). With the engine off (or in boost) typically one or two brake applications and it's gone. No big deal, since you generally aren't applying the brakes when you're in the boost.



And yeah, a one-way check valve would ensure the booster never sees positive pressure.



Any car with low manifold vacuum (or boost) will experience a reduction in power assist for the brakes. You may recall at the height of the runaway Toyota hysteria the discussions surrounding the increase in brake pedal effort in the event that the engine was running at full throttle, since full throttle equals basically zero vacuum in an n/a car.

 

Neat! Good to know.

 

ha i was right FTW........

 

Wait, na cars pull more vaccuum the more you're on the throttle. The problem with toyota's brakes (there was even a recall for this) is that the gasket manufacturer they used for the brake booster used a polymer that normal dot 3 brake fluid breaks down. People and shops were servicing their cars with normal fluid and it was causing that seal to fail in the brake booster. Honda used the same seal in their booster's and had a voluntary recall as well shortly after Toyota started theirs

 

My dad's old truck had vacuum-powered wipers. The faster you went, the faster the wipers wiped. Apparently sitting in traffic in the rain sucked for him.

 

No! Put a vacuum gauge on it. Vacuum is highest at idle with the throttle plates closed. Makes sense since the engine is an air pump and the throttle is closed. Open the throttle and air rushes in and the vacuum drops. Really!



I can't explain the wipers thing.

 

vacuum is highest on decel. if you down shift with the throttle closed the vacuum is higher than idle.

 

I agree.