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The brake Master Cylinder
This series is divided into seven sections:
1 - Why it goes bad
and what it feels like
(and why your pedal goes to the floor)
- Removal and
Part 3 - How to bench-bleed
the new Master Cylinder
4 - What the Master
Cylinder looks like inside
Part 5 -
How the Master Cylinder works, and why the pushrod needs to be set
Part 6 - How to check the pushrod freeplay (a link
to the bottom of Part 2)
to adjust the pushrod freeplay
All pictures can be clicked
on for LARGER versions!
PART 4: What the
Master Cylinder looks like inside
Not all will look exactly like this.
Yours may differ in detail, but the concept is identical.
|Removing the snap ring allows the rear
(second circuit) internals to be removed.
See the screw near the middle? That's the stopper screw. It sets the
rearwards travel limit of the solid spacer. It's what determines how
far back the innards can travel. You can't
remove the solid spacer until that screw has been backed out.
|This part forms the first circuit.
|Inside the plunger (which is part of the
second circuit) is the concave surface the pushrod bears against.
|This is the second circuit. It nests into
the rear of the first.
|The rear plug that the snap-ring bears on.
If you look reeeeal close, you can see the O-rings on the inside and
outside. Those O-rings are what keeps fluid from leaking into your
booster, and are the reason a leaky Master Cylinder shows no fluid loss.
|This is what seal wear looks like. See the
flat spot where the arrow is pointing?
When new, the rubber seals have a sharp point at their open end. This
sharp point has an interference fit in the bore, and thus seals fluid
in. When worn, it loses its interference fit and exerts less pressure
against the bore wall. Eventually, it exerts so little force that it
becomes possible for fluid to squeeze past and allow the pedal to go to
|Given that most premature Master Cylinder
failures are due to corrosion stemming from poor maintenance, let's
have a peek down the bore of this particular failure.
Well, considering I've changed the fluid every year since the car was
new, there is not a single speck of corrosion. The rebuilders are going
to get a first-class core when I finally return this one.
When I first poured the fluid out, there was zero sludge or gunk.
|It's interesting, don't you think? Despite
the ubiquity of Metric throughout most of the world, such odd things as
pipe threads, road wheels, and Master Cylinders are still measured...in