[urq] Brake - hard pedal when panic stopping

[Buchholz, Steven]

... my pleasure!

I'm pretty sure the BMW and other pressure accumulators have been
verified functional in the urq assist system ... the static pressure in
the bomb is somewhat irrelevant ... the real pressure applied to the
system is determined by the pump and relief valve in the valve body.
The only thing is that if the replacement accumulator had a lower static
pressure it would mean that the system could support fewer requests for
assist.  In fact, that's exactly what happens when a bomb goes bad ...
as the N2 pressure decreases it means that there is a lower supply of
high pressure fluid than before, which means that you get fewer pumps on
the brake pedal before all pressure is lost.  

Maurits, from your description I'm thinking that your car is working
fine ... it may be your suspicion that the bomb is "too good" may indeed
be the truth.  If you find that you have brake assist when stopping a
moving vehicle with the engine off (I hope you don't have to steer!) the
system is working.  If possible you might want to try a "dynamic" bomb
test ... don't brake to a full stop in one pedal depression ... try
several stabs at the pedal while stopping to see if you don't notice a
decrease in assist with each depression of the pedal.  

Are you sure that your hydraulic pump isn't driven off the propshaft?
;-)  Audi did this on the 90 GTO cars ... for the alternator, not assist
though ... 

Steve B
San Jose, CA (USA)
> 
> Hi Steven, thanks. If the BMW bomb does not supply the correct
pressure (=53
> Bar). An incorrect specked bomb (more or less Bar) might prevent the
valve
> from (fully) opening or closing. This could be diagnosed as a faulty
valve
> block. What do you think?
> 
> If I drive 60 km\h and turn off the ignition and do a panic stop, I
can easily
> stop the car (feel assistance) and able to lock the wheels with not
much
> effort. Can I assume the bomb is depressurized after such event and of
course
> if I don't start the engine again?
> 
> Problem is I can't get me a rock hard pedal (with the bomb test) but I
do have
> plenty power assistance when the engine is switched off while driving.
> 
> The latter tells me the bomb is pressurized and OK, the first tells me
it's a)
> so good a bomb, it needs 70+ applications, or b) a sticking valve
block
> prevents depressurizing the bomb. In both cases a) and b) this tells
me the
> bomb is pressured and dangerous to remove.
> 
> (Sorry Ben I hijacked your thread)
> 
> Regards,
> Maurits
> 
> 1986 GV (Swiss WR)
> 1985 CGT KV
> 1982 GL DD
> 
> 
>   I suspect that the valve that fills the bomb is not opening, and
that is why
> there
>   is a hard pedal from the start.  The system depends on that pressure
>   built up in the bomb.
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