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hi I'm returns with garage gurus today
we're going to properly bench bleed a
master cylinder a couple of things you
want to make sure that you have on hand
is some wrenches and screwdrivers and a
good depressor for the backside of the
piston
make sure that you have a kit a master
cylinder bench leading kit these are
available from any tool suppliers and
then also make sure that you have the
proper brake fluid before you start the
job we've got 2.3 or dot4 how do I
identify take a look at the cap on the
old master cylinder and you'll identify
right away that it says dot three so
that's the type of brake fluid that we
are going to be using for this system
here a couple other checks that you want
to make before you start the job is to
look at the configuration of the master
cylinders themselves note where the
fluid level sensor is what type of
connector we have on there make sure
that those are the same very important
is to take a look at the backside of the
master cylinders and you'll notice the
sealing device whether it's an o-ring or
gasket whatever it may be make sure that
those are the same we don't want to
vacuum leak from the brake booster very
difficult to find sometimes make sure
the push rod will be the same contact
between the old and new otherwise you'll
have a pedal that it's too low or you'll
have a pedal that has no free play and
the brakes could lock up once they start
to heat up alright so once we've got all
our pieces there one final check before
you start actually putting fluid into it
is to take a look at the connector the
fitting size configuration make sure the
fittings you're going to use are the
same on the old master cylinder in the
new master cylinder so I check it very
quickly on the old one and then if it
fits the new one we're going to be in
good shape this way when we go finish
the job here and go to put it on the
vehicle we won't have a problem with the
wrong fittings connecting to the master
cylinder and have to start all over
again
so that's just a good quick tip so I've
got my fittings in here I've got to Snug
them up let's get them get the master
cylinder installed in the vise I've got
to set a soft jaw clamps here so I
shouldn't cause any damn
to the backside here that could affect
your ceiling there next step is to
remove the cap get my fittings installed
here and I should make sure I snug them
up and you don't have to over tighten
these these are all aluminum you don't
want to cause any damage there but I
don't want any air to leak in there or
fluid to leak out you know but I want to
make sure I don't damage the threaded
areas all right make sure I install my
lines and these lines are just going to
allow the fluid to flow out of the
master cylinder and right back into the
reservoir sometimes I'll have a retainer
here to help do this once I'm going to
put them right down into the bore so as
I depress my pistons I'll be able to
push the air out and it will draw in any
excess fluid so I don't trap in air or
allow to air to come back in so let's
get started here
I'll open up my dot three I try to start
with a new container like I say don't
make them too large break the seal on it
and that way I've got some good fresh
brake fluid once I fill that up you're
going to overfill it at this time it
won't cause any problems and I want to
make sure that it runs down here make
sure I don't have any leaks as we fill
it up the air will start to bleed down
now I do want to make sure that these
lines stay in that master cylinder
sometimes I'll put something in there
too to stop it from allowing the lines
to come back out because I don't want it
to have fluid running all out all over
kind of making a big mess at that time
so I'm just kind of kind of keep those
in there now I want to depress the
pistons fully slowly so that you can
actually start to see the fluid coming
through the lines and the goal is to get
nothing but fluid in those lines so
you'll see air bubbles coming up through
and just do it slowly don't rush it take
your time and you'll get some nice good
clean fluid coming through here and as
you can see these air bubbles start to
rise and I'll slowly come back once
again allow the fluid to run down into
the master cylinder before you depress
again and as you see there's more very
small tiny air
bubbles that is coming out of here and
we're looking pretty good shape here
because we're getting most of the air
out as you can see it push out I got a
little tiny air bubbles here giving it
just a moment okay so this will take
just a few moments as you can see there
are very tiny air bubbles that are still
starting to rise here so I'm not going
to rush the job if I try to rush the job
put the master cylinder on the vehicle
itself all of a sudden I've got a spongy
pedal and I can't get the air out
because the master cylinder is sitting
too far tilted backwards or forward when
I'm on the bench here I can do a number
of things I can remove the master
cylinder and rock it back and forth I'm
pretty parallel right here
I am slightly tilted up I've got a port
that's coming all the way to the front
of the master cylinder so my I have a
good opportunity to get all of the air
out and I'll depress it once again you
can see some very very very fine air
bubbles that are in the system and in a
worst-case scenario make sure that you
properly tighten the fittings I feel
pretty confident but I'm going to double
chuck it anyways just to make sure
because if you're drawing any air into
those fittings that could cause the air
that you'll see in those lines
okay after being very patient and
checking to make sure that all of our
connections were extremely tight we are
now in good shape we finally have gotten
the air out so don't rush the job as
you've seen here very often you'll be
pushing it very quickly you'll get small
bubbles in here I know that you're
trying to get the job the customer's
probably waiting so take your time be
very very thorough and once you do that
you'll find out you'll have no more air
bubbles coming through here and you'll
have good success when you go to install
this master cylinder so thank you for
watching and we appreciate your business
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