Re: Pressure Relief Valve?

["Fred Munro" <munrof@isys.ca>]

Jeff;

    If fluid is coming out of the top of the reservoir when you brake, it
sounds like your servo is passing fluid from the accumulator much faster
than the pump can pull it from the reservoir to fill the accumulator. This
is odd, though, because if the accumulator is fully charged and the
reservoir is filled to the "max" mark, completely discharging the
accumulator (by pumping the brakes with the engine off) will fill the
reservoir but not overflow it - I just tested this on my '91 200q after
replacing the bomb. In theory, the reservoir shouldn't overflow, although I
have seen posts on the "volcano syndrome" in which the overflowing reservoir
is the sign of a bad pump.
    Is your reservoir filled too full by any chance? Have you tried the
servo test to check the brake servo?
    Orin Eman posted on October 4 a description of his tussle with the
pressure relief valve. I have attached it for your convenience.

HTH
Fred Munro
'91 200q  262k km

Orin Eman wrote:

Some repair kits have a fairly large o-ring that doesn't seem
to have anywhere to go... no mention of it in the 5k or 200
Bentley.  A while back Scott Mockry told me it goes under
what the 200 Bentley calls the pressure relief valve retainer.
Well, my resealed pump was leaking again at the seam, and my
resealed spare leaked worse!  So, I attacked the original pump
today.

On taking it apart, the 6 o-rings and the large o-ring between
the two halves still looked fine.  So it was time to pull
the 'pressure relief valve retainer' out.  It's won't move,
so I started with the pressure relief valve (it has an
allen head and is recessed).  The retainer broke loose before
the valve came out, but then stuck.  I had to grab the
retainer in the vice and turn the rear pump housing by hand.
It came off - under protest.  Sure enough there is the remains
of an o-ring under there.  About 1/2" of the threads on the retainer
are destroyed - there is some kind of glue/sealer on the threads.
I clean the threads up a little and clean some of the sealer off the
o-ring seat before putting it back together.

I finished the reseal as normal and put it back in the car.
Center seam seems dry so far!

The 200 Bentley says that if there is more than 0.2mm between
the retainer and the pump body, discard the pump.
I guess the reason is that the retainer is supposed to be
glued in for the life of the pump.  If it works loose,
the pump is going to leak and a normal reseal won't help.
With the glue, it is unlikely that it can be extracted without
destroying the threads...  and it would need re-glueing.

Incidently, the 200 Bentley makes no mention of replacing the
pressure relief valve whereas the 5k Bentley does.  I wonder if
that's because attempting to break the valve loose tends to
break the retainer loose.

The latest reseal kits don't have this 'extra' o-ring.  It was
in the first kit I bought and I saved it just in case :)

Orin.
-----Original Message-----
From: Ron Mruss <rmruss@pangea.ca>
To: 'Quattro List' <quattro@coimbra.ans.net>
Date: Sunday, November 08, 1998 6:05 PM
Subject: Pressure Relief Valve?


I was hoping someone might be able to help me with this as I am continuing
to have problems with my hydraulic system.  Bomb is fine, pump does not
appear to be putting out enough pressure to steering or braking systems -
when I brake, it seems to force hydraulic fluid back into the reservoir -
not a good thing.  The Bentley mentions replacing the pressure relief valve,
but I couldn't find any references in the archives using the search engine.

My pump is not leaking, nor does anything else seem to be, I only lose fluid
when I brake and it comes out the top of the hydraulic reservoir.  So, has
anyone replaced the pressure relief valve in their pump?  Cost?

TIA,


Jeff Mruss
'84 5KS