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Clutch Master and Slave Cylinder Replacement and Bleeding Techniques


Welcome to Perfection Clutch Installations
Lab. We just finished putting a clutch in this Hyundai Elantra, now we’re
going to replace the master cylinder and the slave cylinder, and we’re
going to bleed this system using a push back bleeding technique. We’re not
going to push fluid out the bottom of the slave cylinder, we’re going
to push air bubbles out the top. Now I went ahead and put one bolt back in
to secure the slave cylinder while I remove the bold that holds the line
on, so I’m going to use that to just secure it and start to remove that bolt. Now to remove the master cylinder, couple
different things I have to do. Inside there’s merely a pin and clip, so I
pull the clip, pull the pin, that’s easy. Now here on the outside, I’ve
already disconnected the bolts that hold the reservoir in place, I can get
those out the side. I’ve made a couple cable disconnects here, just to get
the cable out of the way a little bit. I’ve got two fairly interesting
setups. To remove the line from the master cylinder, I’m using what’s
called a crow’s foot, but on the bottom, the master cylinder is mounted to
the firewall with two nuts, and pretty deep back in there so I’ve got a long
extension, a swivel, and a socket. Okay, this is the crow’s foot on the
line going down, and that came off quite nice. Well now we’ll go ahead and install the master
cylinder. So mechanically, all we do is push it through the hole in the
firewall, here’s two studs, get it lined up, now hopefully the nuts won’t
fall out of the socket, there’s the first one, here a little tighten
to wrench it. I want to attach the line. Okay, that’s started. Now
before I tighten that up, I want to go ahead and attach the line that
goes to the slave cylinder itself, and snug it up, okay? Now I’m going
to change the wrench, use the crow’s foot again, and tighten the line and
into the master cylinder. Boy that crow’s foot is working out well today. Now maybe this will help people understand
about changing brake fluid every so often. This is just full of black sludge
in the bottom there. I don’t think this fluid’s ever been changed out.
So before I install this reservoir and line, I’m going to clean these
two out. A lot cleaner in there now, that was 10 year
old grunge. So remove the cap, kind of hard to see but we’re getting
that clamp, down in place, there it is, got it. Okay, now we’re going to go
ahead and attach the line through the slave cylinder. There’s two copper
compression gaskets, put one in each side of your bolt, and then there’s
a slot in the back of the slave cylinder that the stem actually goes
through, and before I get real tight with this, I’m just going to put a drop
of DOT 3 on there, just act as little bit of lubricant. Now for the fun part, bleeding it. I’m personally
not a big fan of putting brake fluid in and pumping on the pedal, and
saying open the bleed screw, yes, that has its place, but then a clutch
we have a couple different situations we can work with. First, in this
particular situation, I’m going to just allow it to gravity bleed. So
I’ve got a tube on the slave cylinder, going down to the basin, and the
slave cylinder is an angle where the bleed screw, I’m going to try to hold
it, where the bleed screw will be just about at the highest point of my system.
It’s a little bit challenging with this line, but that’s going
to be my first effort, is just a gravity bleed. And after we get as much
fluid as possible, then I’m going to push back on the slave cylinder,
just with my hand, and try and push air bubbles out and up the top. So let’s put some DOT-3 in there and see what
happens. Always clean DOT-3 from the sealed container, never never use
waste fluid, don’t recycle it like that. I’ve already loosened the bleed
screws so it shouldn’t take much, and hopefully we’ll get some fluid coming
out. And the fluid level’s dropping in the reservoir, that’s good, fluid
going in, we’re just going to let that run a minute, keep a wet towel handy.
Now we already got fluid coming down here, looks pretty clean. I did
blow the lines out with compressed air, the rubber and the steel line,
that’s looking good already. Oh, there’s some air bubbles, see them? I
don’t know if you can see them in the camera, but there’s air bubbles coming
out the line right now. Okay, I’m going to go ahead and close the
bleed screw. I’m trying to give you an overview so the camera angle may not
catch every single detail. I want you to see the parts as I’m working with
them. All right. I’m going to snug that up a little bit, and check the
reservoir. Now the slave cylinder is extended all by itself, because
there’s a spring inside. So now I’m going to carefully start to compress
the slave cylinder, just by hand, and watch the reservoir. Have one bubble
come out so far. There’s some bubbles. You can still see some air bubbles
coming out. It’s looking pretty good. That only took a few minutes
of compressing the slave cylinder to act as a pump, and push air bubbles
up and out of the top of the reservoir through the master cylinder. But how do you know when it’s completely bled
and you got all the air out before you hook it all up? Let me use the
old slave cylinder and I’ll show you one way, one technique. I’ve got a C-clamp
here. Now inside here I put a socket, a small socket, to go between
the C clamp shoe and the piston of the old slave cylinder. At the opposite
end, the C clamp is pushing against the nut right there. So this creates
that brick wall effect, and you can not extend that slave cylinder at
all. So you get a hard pedal when it’s blocked like that, no air. If it
had air you’d feel it. Now the other thing that’s critical is the
setup of the push rod length. Right now, notice, I can compress the slave
cylinder with my hand quite easily, compressing it, and the spring inside
the slave pushes it back, that’s good. Steve, would you extend the push
rod length, please? Now Steve has extended the push rod, now I can’t
compress it. Steve has made it too long inside there, and either the check
valve is positioned, or the piston port is positioned, so that fluid can
not go back into the master cylinder. This is incorrect. This would have
the effect of holding the foot on your pedal as a system starts to age.
Stee, would you shorten the length of the push rod? Now Steve shortened
it, and I can press it again. So if you don’t happen to have the factory
setup measurements, remember this, you must be able to compress the slave
cylinder freely, that’s an indicator that everything is set up correctly
in the master cylinder. We bled this by gravity bleeding and by pushing
the slave cylinder in against it, and forcing air bubbles in and out, we
tested it to make sure it was bled, we’ve checked to make sure that it has
the ability to be compressed, and pushed the fluid back into the master
cylinder, I think we’re all done. If you have any questions about a clutch,
a hydrolic system, or a flywheel, please call Perfection at 800-258-8312, press
4, your call will be routed to Tony, Steve, Bobby, or myself. We’ll be
glad to help you out.

8 thoughts on “Clutch Master and Slave Cylinder Replacement and Bleeding Techniques

  1. Thanks. That was really informative. Didn't realise you could remove air bubbles by pumping the slave – it seems easier actually.

  2. You say "Always (use) clean DOT 3…" which is very misleading. You should ALWAYS USE WHAT'S RECOMMENDED FOR YOUR VEHICLE. I know you meant to emphasize the use of 'clean' fluid and not necessarily 'DOT 3', but to people that don't know this could lead to using the wrong fluid.

  3. Don't you have to compress the master cylinder at the pedal?? I was told you had to cause it called priming the master cylinder. I did all of this and my pedal is spongy

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