[V6-12v] stopping problems

[Frank Chapchuk]

Eliott's description is correct. My car ('92 100) originally had some sort 
of vacuum pump, but that was replaced during a recall and now gets its 
vacuum from the engine. The connection from the engine to the area by the 
master cylinder is done with many different hoses (plastic and rubber), Y's 
and T's and check valves. I took a quick look at some of the hoses and two 
of them are deteriorated.....very soft. So soft I can grab the hose and 
stretch it like a rubber band. I'll replace these and see it if fixes the 
problem


----Original Message Follows----
From: Elliott Potter <mailinglist at eep.burdell.org>
To: mike <mikemk40 at yahoo.com>
CC: V6-12v at audifans.com
Subject: Re: [V6-12v] stopping problems
Date: Sun, 1 Aug 2004 19:50:31 -0500 (EST)

I'm frequently wrong about this stuff, but I still disagree:

On Mon, 2 Aug 2004, [iso-8859-1] mike wrote:
 > The v6 na cars have the bomb too...

The "bomb" on 5-cylinder cars is a hydraulic pressure accumulator, which
has three hose connections (two are 2000+ psi hydraulic connectors),
whose function was to maintain *hydraulic* pressure.  This was necessary
because turbo cars used a hydraulic brake boost system, as opposed to a
vacuum assisted brake system, and the bomb (which was charged with
high-pressure nitrogen) was there to maintain hydraulic pressure to the
brake system.  It's called a bomb because it looks a bit like the German
M24 and M34 ("potato masher") grenades.  I don't know for sure if non-turbo
5-cylinder cars had this but I don't think they did.

Cars with the 12v V6 use a vacuum assisted brake system, and do not need
a hydraulic pressure accumulator.  What the 12v V6 _does_ have is a
vacuum reservoir, which is a round plastic ball that sits in front of
the intake manifold next to the ignition coil packs.  It looks a bit
like the ACME brand bombs you see in cartoons, so I guess you could call
it a bomb, though it's less likely to explode if mistreated like the
turbo cars' bomb is (since it's just an empty plastic ball).  The main
function of the vacuum reservoir is to provide vacuum for the intake
manifold changeover valve, since that valve operates at high engine RPMs
where the vacuum provided by the engine is reduced.

The vacuum brake booster gets vaccum from a different part of the engine
and is not connected to this reservoir.

Having said all of that:
- the large diameter vacuum lines that feed the brake booster do tend to
   crack, and that could cause braking issues (though it's not as
   likely).  Those lines plug in to the front of the intake manifold
   unless you have a very early 1992 build.
- the connection to the vacuum reservoir commonly cracks, and the
   resulting vacuum leak can cause the sorts of problems that vacuum
   leaks normally cause; generally rough running and/or CELs.

*shrug*  Like I said, I could be wrong on this.  I'm not doing a very
good job of keeping up on 12v trivia since I don't have a 12v car
anymore.
--
Elliott
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