Re: Bomb Gas Pressures

[Phil and Judy Rose <pjrose@servtech.com>]

Eric,
Yes, I'm certainly aware of Audi's intent in the design of the accumulator.
However I was proposing that accumulator pressure be released NOT when the
engine stalls or dies, but after the ignition is switched off (we _need_
another relay to worry about, right?). I would think having brake boost
under **ignition-off** conditions isn't a high priority particularly _if_
the alternative could extend significantly the useful life of the system.
Seems that the occasions you might need brakes with the engine switched off
are when the vehicle is near a standstill anyway.

As to my two dudly bombs: I agree it's not something to dawdle too much
over. They've already been scheduled for replacement.

Phil

>
>Phil-- pressure in the hydraulic system is maintained by the accumulator
>when the engine is off to ensure that you've still got power brakes if
>the engine STALLS for any reason.
>
>Have you ever driven a 5000/100/200 with a bad bomb??  I almost lost it
>in a customer's 200Q wagon on an off ramp due to the accumulator not
>doing it's job.  Trust me, it's not fun losing hydraulic system pressure
>while panic braking from 80 mph, which you may have to do some day with
>a stalled engine.  (Ever run out of gas on the expressway?  Ever end up
>with a dead battery from a bad alternator or broken alternator belt on
>the highway?)
>
>>From all of your questions regarding bomb rebuilding, it sounds like
>you've got a bad bomb now-- perhaps you haven't really had to stomp on
>the brakes yet, but I guarantee you that under heavy braking, you won't
>just feel pulsation from the hydraulic pump, you'll LOSE boost.
>Suddenly the pedal will get rock hard, and you'll have to stand on the
>brakes with all of your weight to avoid mowing down that
>deer/child/senior citizen/pole.  Keep in mind that 5/6 "cylinders" in
>the pump supply pressurized fluid for the rack, which requires a high
>volume of fluid under pressure.  Only one of the pump's cylinders
>supplies pressurized fluid for the brake servo, which requires a
>comparatively lower volume of fluid.  (Think of the cross sectional area
>of the steering rack compared to that of the piston in the brake
>servo.)  In addition to dampening pulsations from the pump and
>maintaining pressure when the car is off, the accumulator also ensures
>that in the rare instance that you need a higher volume of pressurized
>hydraulic fluid for really hard braking (the piston in the servo is
>extended farther than usual, for more time than usual,) you'll have it.
>Give your bomb a big kiss for saving your life.
>
>Eric.


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