[urq] Brake - hard pedal when panic stopping

[Buchholz, Steven]

As Maurits stated, the "valve body" (probably not the official name) is
the squarish plate that the bomb screws into.  Unlike the newer cars,
the urq's hydraulic assist system uses an independent pressure regulator
... and it really isn't anything more than a heavy duty ball with a
diaphragm with one side of the diaphragm pressurized with Nitrogen.
While I imagine anything is possible, I'd be skeptical that you'd get a
bad bomb (did it have an expiration date?  The nitrogen does leak past
the diaphragm over time).  The pressure relief valve that returns any
excess fluid to the reservoir is in the "valve body".  There's a great
schematic diagram and description of the system on pages 44-50 of the
IST doc:

	http://www.quattro.ca/Urq/urq-IST-Introduction.pdf (thanks
Martin!)

It sounds as though Maurits' car has the same system as we do ... i.e.
the one described in the above document ... and in his case, 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.  While it is always recommended to be careful when
dealing with the bomb due to the potential of releasing high pressure
fluids, I don't think that you could have a situation where pressure
builds up in the pressure accumulator and stays there without providing
any assist ... so I don't think there's a problem removing the suspect
bomb ...

Steve B
San Jose, CA (USA)
> 
> I'm having exactly the same problem (and an additional soft pedal with
> ticking noise when standing still only with running engine). I changed
the
> bomb but unfortunately this did not fix it. The bomb I'm using is not
an
> Audi-part but a BMW 5-series aftermarket Febi Billstein P/N 01817. I
do
> suspect this to be a) broken, or b) not spec'ed right like the
original.
> 
> When I try the bomb test it is not possible to get a rock-hard pedal
and the
> ATF container level wouldn't rise either, so I suspect the bomb is
full with
> fluid but can't get it out. Because It might still be charged I'm
afraid to
> switch it back with the old bomb. I'v already changed the BMC and
> proportioning valve, both OEM.
> 
> 
> If you accelerate hard, does the pedal feel harder with even more
delay? And
> if you drive normally, the pedal/brakes also feel normal?
> Did you change your bomb yet? Is your pedal "hard" when the engine is
> running / standing still? What have you done to fix the problem?
> 
> PS The valve block is where the bomb is screwed/mounted in and has 2
heavy
> lines to the steering pump and brake servo.
> 
> ----- Original Message -----
> 
> 
> The pedal is hard from the get go and only goes soft after depressing
the
> pedal - as if there is some delay in actuating the brakes.
> 
> What do you mean by valve body - is that in the master cyl., booster,
> somewhere else?
> 
> 
> [Date: Mon, 11 Jul 2005 09:15:52 -0700
> 
> ... this is the classic symptom of a failing bomb ... but it could be
> the valve body too.  When you shut off the engine how many brake
> depressions do you get before the pedal goes hard?