QThe cutaway of the original master
cylinder shows the straight bore and
pistons—OK for drums that have
retraction springs and early discs that
didn’t retract.68 MUSTANGMONTHLY.COM
VINTAGE TECH ADVICE
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BEYOND THE BASICS Dave Stribling TEXTPEDAL PERFECT
R
on Sams from Mont-
gomery, Alabama,
wrote me a very
detailed note about
some of the issues he
had after installing a four-wheel disc
brake setup on his 1969 Mustang (it
was long, so I am summarizing). After
installation of the system, he noticed
that the pedal travel length was exces-
sive, and it didn’t feel like the pedal
was really engaging until the very end
of the pedal travel. After checking
all the standard items (proper bleed,
booster pushrod length, pressure at
the calipers), nothing came back nega-
tive. Ron then took the recommen-
dation of a friend and tried a quick
take-up or step-bore–style master
cylinder, and this brought his pedal
control back to a manageable level.
Everything he installed was working
properly—but not together. Let me
explain what Ron found.
If you remember, original Mustang
disc brakes would not retract from
the rotor; they would slightly drag
against the rotor. Drum brakes retract
with a spring (which is why drag rac-
ers bought big-block cars with drum
brakes), so they don’t drag. Manu-
facturers since then have developed
low-drag brake calipers, which pull
the pads back from the rotor and are
more fuel efficient. As you also know,disc brakes use more fluid than drum
brakes, hence the bigger reservoir in
the tandem master cylinder. So, when
the already fluid-hungry disc brakes
retract back and pull more fluid back,
more fluid is required to engage the
pads against the rotor. To get more
volume requires a larger-bore master
cylinder, but the bigger the bore, the
more pedal pressure needed to get the
pressure up to a required point.
That’s where the new quick take-
up master cylinders come in. They
have a larger primary chamber that
feeds more fluid at a lower pressure
to quickly fill in the needed extra fluid
for the calipers. Now, why don’t the
manufacturers provide this style of
reservoir with their systems? I can’t
answer that, but one reason may
be that your system is an old-style
double-flare setup, and most modern
brake systems use a European bubble
flare, so mating the two can be a
challenge. Ron found that a 1988
Thunderbird master cylinder did
the job for him, and I have used the
1993 Thunderbird Super Coupe
four-wheel disc master in some of
my applications.
Thanks for the info on the new
braking systems, Ron. If you are hav-
ing the issue of the pedal having an
unusually long pedal travel to engage,
this may be something you should
look at.QA modern-style quick take-up or step-bore master
cylinder reservoir in the primary piston bore (rear)
pushes a greater volume of fluid around the primary
piston to fill the void on modern low-drag calipers.
The system can then build pressure once the volume
required is added.QThis setup uses a Mustang Steve (mustangsteve.
com) 9-inch booster and a 1993 Thunderbird master
cylinder made for low-drag four-wheel disc brakes.
The outlets are on the outside for tight engine
compartment installs.