[s-cars] soft break pedal

[Nicholas]

So now my brake warning light hardly ever comes on (not sure what to
make of that) and bleeding the brakes didn't seem to get rid of my
pedal-travel issue. And I'd be surprised if that had anything to do
with the intermittent warning light.

On the syncronized forum (I've got a Quantum Syncro Wagon too),
someone just mentioned that they are having the same issue and
replaced pretty much everything in the brake system before replacing
the brake booster. Turns out their booster had corroded on the inside
and very little was left of the diaphragm.

So, could I just have a worn-out brake booster? I plan on pulling mine
and shaking it so see if it feel like anything is rotten or loose in
there (a preliminary test for sure).

Searching for possible replacements I found a wide, wide range of
prices and images of what the booster actually is:

http://www.partsgeek.com/ymm/1992/audi/s4.html?category=brake&part=brake_booster

http://www.theautopartsshop.com/power-brake-booster/cd532671.html

...which one is (more) right?

Or, am I barking up the wrong tree here?

Cheers,
-Nick

On Mon, Nov 28, 2011 at 4:37 PM, Nicholas <applen at gmail.com> wrote:
> Reservoir level hasn't changed and I see no signs of leaking fluid in
> the obvious places, but haven't traced the lines from end-to-end.
>
> I'll try the bleeding again with the proper sequence and also check
> for bulging lines (I'm assuming the only flexible/bulge-able sections
> are those near the calipers for steering and suspension
> articulation...correct?).
>
> While bleeding I had positive pressure the whole time (even before I
> started pressing the pedal)... is that normal? Do I need a vacum pump
> to bleed properly or is the hose/jar full of fluid method sufficient?
>
> Lastly, is the consensus that the bomb the most likely culprit for the
> intermittent brake light? Is there anything else electrically on the
> fluid side that could be sending that signal? It sounds like I should
> go ahead and preemptively tackle that regardless of my soft pedal...?
>
> Thanks lots,
> -Nick
>
> On Sat, Nov 26, 2011 at 4:18 PM,  <racingiron at comcast.net> wrote:
>> Soft pedal does usually indicate problems on the brake fluid side... either
>> air in the system or possibly a bad line that bulges under pressure.  I
>> presume you've checked to make sure you're not losing fluid somewhere.
>> Closely inspect the flexible lines as someone applies pressure to the
>> pedal.  AFAIK, the only part of the brake fluid side that will activate the
>> idiot light is the level sensor in the reservoir.  You can unplug the
>> connector from the sensor (may need to jumper it--not sure if it's normally
>> open or closed) to see if that gets rid of the light.  I suspect the light
>> is from the boost system due to a tired bomb, but unrelated to your pedal
>> pressure issue.  Oh BTW, brake bleeding is usually done by starting at the
>> furthest caliper from the master cylinder and working forward (i.e., RR, LR,
>> RF, LF).
>>
>> Eric R.
>> '86 urq
>> '92 urS
>> '93 urS
>>