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RE: "Bench bleeding" brake master cylinder.

To: "'Edwin Vaughan'" <vaughme@mail.auburn.edu>,
Subject: RE: "Bench bleeding" brake master cylinder.
From: "Kulka, Matt" <Matt.Kulka@hboc.com>
Date: Fri, 2 Apr 1999 14:46:24 -0500
Edwin,

Well, since no one else piped in, I'll have a go.  Long, drawn out posts
describing basic procedures based on general theory without any specific
application are my specialty.  

The idea is to get all the air out of the passages of the master cylinder
(M/C) so you don't have to pump so much down to the wheels and bleed it out
there.

There should be some odd little bits in the M/C box:  Two plastic fittings
that fit into the M/C outlets, two bits of plastic hose and a little clip
like a spark plug loom that will hold the hoses.  Screw the plastic fittings
into the M/C outlets.  Connect one hose to each fitting.  Put the other end
of each hose into the reservoir so they'll be below the level of fluid.  The
clip should hold them there for you.

Gently clamp the master cylinder in a vice.  Use a bunch of rags for padding
and be very gentle.  I'm not buying you a new M/C if you crack this one.

Fill the reservoir with brake fluid.  Put a dull phillips screw driver into
the hole where the pedal push rod will go.  Gently push on the screwdriver
as if you were the brake pedal actuating the piston.  Watching inside the
reservoir for tiny bubbles coming out of the little hoses.  Continue until
you no longer see bubbles.

I tend to do this with tiny little strokes, not a full stroke of the
cylinder.  Aside from not wanting to create a tempest in the reservoir I
can't recall why I do it that way (except that's how I was taught).

Anyway, once you have this done, you have to figure out how to get the M/C
into the car without letting any air back in.  If it came with plugs in the
brake line fittings, you can try to unscrew the plastic fittings and put the
plugs back in.  If not, then you can leave the plastic fittings in and try
to crimp them or the hoses shut.  No matter what, you're going to: 

a) Lose some drops of fluid when you disconnect (and reconnect) the brake
lines, so put down a lot of rags before you start.  (Unless you wanted to
strip your paint anyway.)

b) End up with some air in the lines, so bleed your system real well
afterward.

Best of luck.

Matt Kulka
Huntersville, NC
'74 B - with a master cylinder in the box, waiting for family duties to let
up.

-----Original Message-----
From: Edwin Vaughan [mailto:vaughme@mail.auburn.edu]

I got a rebuilt master cylinder today. The pamphlet that came with it said
something about "bench bleeding" the cylinder. I have no idea how to do
this, would someone explain the process, please?

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