At 02:07 PM 2/22/2002, Robert Keezer wrote:
>Beginning about a week ago, my brake pedal goes to the floor slowly at
>stops and then the Vanagon has little braking and starts rolling.
>The first thing I thought of was "vacuum check valve". I looked for it and
>was gone, having been replaced with a short length of plastic tube. I am
>surprised by this, because I don't remember removing and not replacing the
>check valve. I know there is supposed to be a check valve. So who knows
>for how long the check valve has been missing.
>So I replaced the tube with a proper check valve, but the pedal still
>won't hold, and goes to the floor.
>The questions are: Can driving missing a check valve  ruin the vacuum
>brake booster?

I doubt it, but in any case it's not relevant -- there's a direct
mechanical connection all the way from your foot to the master cylinder
piston.  The booster simply helps you push.  Total failure of the booster
would not cause a sinking pedal.

>Or, can a bad master cylinder be the problem?
>Are the symptoms of a bad master brake cylinder as described?

Yes and yes.  If the pedal is sinking, one of these things must be true:

1) air/steam/vapor in the system, making a compressible link between master
and slave cylinders.

2) fluid getting pushed out of the system through a leak in lines or
cylinders (in which case of course there will be air in the system as soon
as the reservoir empties).

3) fluid recirculating inside the master cylinder.

david

--
David Beierl - Providence, RI
  http://pws.prserv.net/synergy/Vanagon/
'84 Westy "Dutiful Passage"
'85 GL "Poor Relation"