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Re: Weird brakes

RC Ringlien wrote:
> Phil Payne wrote:
> >
> > In message <33AD174D.BF8@isd.net> RC Ringlien writes:
> >
> > >    To sumarize: all 4 brakes drag after car heats up (approximately 5
> > > miles of driving) and the engines has to really work to overcome this.
> > > I've deduced that the bomb is probably shot.  The brake light blinks
> > > after stabbing the pedal, but I only start to loose boost after
> > > everything heats up.  When car is cold and ignition off, I can pump the
> > > brake pedal 20 times before I start to loose boost. A Robert Russell had
> > > the same dragging problem a while back but I can't locate the message in
> > > the archives and lost his address in an e-mail crash.
> >
> > I don't think it's the bomb.
> >
> > I also don't have the official 200T documentation, so the following is
> > speculation:
> >
> > Do you have the later type of "bomb" - usually mounted with its axis
> > horizontal - and _TWO_ sensors attached to the casting at its base?
> >
> > If so, the axis of one of the sensors (supply pressure) is parallel to
> > the bomb's axis, and the axis of the other (bomb pressure) is at right
> > angles to it.  Disconnect the first and see if your "stabbing" light
> > still comes on.  If I'm right, it won't.
> >
> > I suspect that the brake servo itself is leaking internally into its own
> > return line.   There are two types of servo fitted to the later cars -
> > from the factory they mostly came with cast-iron cylinders but
> > replacement parts have been light alloy since 1987.
> >
> > --
> >  Phil Payne
> >
> >  Phone: +44 385302803  Fax: +44 1536723021  CIS: 100012,1660
> Phil:
>    Thanks for the quick reply.  My pressure accumulator(bomb) has no
> sensors, only the three hydraulic connections--pressure/damper hose from
> the pump, pressure line to the servo, and return line from bottom of
> plastic reservoir. The sending unit for the brake light is on the servo;
> it is here where the VW1441 gauge is connected, if I had one. The bomb
> is mounted horizontally down low on driver side under the ABS unit.
> There is some corrosion on the fitting of supply hose from the pump.
>    If the servo is leaking back thru the return hose, how can I test for
> this?  Would I see a lot churning in the supply bottle during this
> failure mode.?  As it's obvious that heat brings this failure on, is
> some expansion situation causing servo to not allow master cylinder
> brake fluid return?  One local mechanic thought my brake rod was
> adjusted too long ; backing it off changed nothing.  Bob Russell, if you
> are reading this, did you find a solution for the same problem?
>    Still puzzled here with the hood up;luckily we do have other wheels
> in the family.  Hate to say it's an american minivan.
> Bob Ringlien
> rringlie@isd.net
There have been similar problems reported in the List. I believe the
origin of the problem is in the master cylinder.. internal corrosion..
apparently the valve  controlling the action of the booster cylinder
leaks and allows booster pressure without break pedal action. If I
remember correctly, the cure is:
Flush brake system, replacing the "brake fluid" and bleeding all four
Replace master cylinder.
You may check "the archives" for further info.
Good luck !!!