Replacing Master Cylinder 5KCSTQ, update

[Erik Gerrits]

I left out a major point before I posted.  The rear
brakes aren't engaging.  I have removed the rear
proportioning valve and tore both calipers apart to
make sure that there wasn't any seized pistons.  The
brakes bleed fine but there doesn't seem to be enough
pressure to engage them.  I am at a loss and since the
MC cost $43 for a reman from Napa I figured that I
would replace it to take it out of the equation.
Thanks,
Erik Gerrits

--- Kneale Brownson <knotnook at traverse.com> wrote:
> At 08:11 AM 02/19/2002 -0800, Erik Gerrits wrote:
>
> >I watched as someone pumped the brakes on my car
> >(while running) and I could see a drip of brake
> fluid
> >come out of back of the master cylinder (where it
> >bolts on).  Two questions, should I replace the
> master
> >cylinder?  And if so is there anything special that
> I
> >need to know?  I don't have the Bentley book,
> >unemployed at the moment.
>
> How do you know it was brake fluid, Erik?  There's a
> drain hole in the
> bottom of the spot where the MC bolts to the brake
> booster that, I presume,
> is intended to allow condensation to drip out.  One
> of my Audis on which I
> changed the MC had a big collection of rust plugging
> that hole.  I can
> picture moisture dripping out of such a situation
> when the rod connecting
> the booster with the MC moved.  The fluid also could
> be hydraulic oil from
> the booster system, although I'd much rather change
> a MC than a booster.
>
> If it IS brake fluid, there's a rubber seal at the
> back of the MC housing
> around the actuator rod that probably is leaking.
> That shouldn't cause
> problems with braking as long as you keep the brake
> fluid level up.  But it
> may be indicative of additional deterioration in the
> MC assembly.
>


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