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RE: I don't understand the bomb!
Since you think it is good info. I will forward it to the list.
> From: Wallace White[SMTP:whitew@leland.Stanford.EDU]
> Sent: Monday, May 18, 1998 11:28 PM
> To: Russ Southelrin
> Subject: Re: I don't understand the bomb!
> Russ -
> You're the winner of the "best explanation of the bomb" award. I've
> forwarded it to Dick, who just asked some bomb-P/S questions, which it may
> partially answer.
> > Wallace,
> > Most normally aspirated cars have a good supply of manifold vacuum for
> > the power brakes to be "vacuum" assisted. This means that the heavy
> > brake pedal you feel when the car is turned off is from the engine not
> > producing any vacuum and therefore no vacuum assist to the power brakes.
> > Now a turbo charged car runs under positive manifold pressure most of
> > the time so there is not much of a good source of vacuum for power
> > assist. So the Audi engineers in their infinite wisdom decided to make
> > the power brakes hydraulic assisted. This means that the additional
> > "assist" that power brakes afford is supplied by the hydraulic
> > pump/power steering pump. The hyd. system stores the hyd. pressure in
> > the bomb. This is a rubber diaphram that sort of inflates as the hyd.
> > pump puts out something like 1500psi against it. All it is a pressure
> > accumulator. An analogy would be if you blew up a balloon with air you
> > would have a volumn of stored air at the pressure of the balloon.
> > When the bomb goes bad it does not store (accumulate) much volumn of
> > hyd. fluid and therefore you will lose power assist (pedal goes hard)
> > upon pumping the brakes.
> > If your hyd. pump is in good working order then it can supply enough
> > pressure for light braking but under emergency braking you might lose
> > the power assist.
> > Some normally aspirated cars have hyd. assist and a bomb also (mid 80's
> > BMW 5 series for one). Some turbo cars have vacuuum assist. I think it
> > was a German thing that they thought it was superior engineering?????
> > Hope this helps
> > Russ