[Vwdiesel] brake servo

[lbaird119 at aol.com]

  Initially it sounds like the servo's bad but then the assist WILL go away with a few close-together applications of the brake pedal.  More often it's a weak vacuum pump.  If you have the diaphragm type it could be the diaphragm starting to go or a leaking valve.  If it's the sliding vane type, cleaning it could help, otherwise it takes some machinin/filing to get the clearance to the lid reduced.  The vac line to the servo can get cracks and leak.  The slow leak (depending on how slow) could be typical, a small leak around the master cylinder or a genuine leak in the booster.  They seem to dump a certain amount of vacuum when applied.  Haven't tested to see if that's a function or from impending demise.
    Loren



-----Original Message-----
From: Dianne Roa <dianneroa at gmail.com>
To: vwdiesel <vwdiesel at vwfans.com>
Sent: Sun, Sep 23, 2012 10:22 am
Subject: [Vwdiesel] brake servo


I have a 1984 VW Rabbit *diesel*.  When I push the brake pedal down, there
s a hissing sound.  The first time I push the pedal down, the brakes work
ine.  If I pump the brakes several times, the vacuum assist from the brake
ervo goes away.  I put a vacuum pump on the brake servo input.  I created
 vacuum on the brake servo and it gradually leaks down.  Also when I put
he vacuum on the servo I can hear a slight leaking sound.  If I put the
acuum on the servo as soon as I push the pedal down it goes to zero.  I am
ot absolutely sure if the problem is with the servo or the vacuum pump.
Bob Roa
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