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That's The Brakes: Restoring and tweaking 4-piston disc brakes.

Story and photos by RICHARD EHRENBERG.
Copyright © 1995 Richard Ehrenberg. Used by permission. First printed in Mopar Action

Hold
everything! We're absolutely not gonna sit here and tell you that
ya oughta swap your classic A, B, or E-body Mopar over to fixed-caliper
(4-piston) disc brakes. If you need more brakes, a swap to the later
single-piston setup is clearly the way to go, based on brake size,
serviceability, and parts availability. If you're not sure about the
best way to go about the swap, you can refer to our article on the
subject which has become virtually the reference work. It first
appeared in High Performance Mopar (Summer 1988), then an
updated version was published in Mopar Action (12/89), and again in the
first issue of Mopar Tech Special. To the best of my knowledge, all of
these are now out of print, but it also appeared in the 11/94
issue of Popular Hot Rodding, which does have back issues available.
What you don't want to do is swap knuckles side-to-side for
swaybar clearance, use taller F/J/M or late-B-body knuckles, or any of
the other tomfoolery suggested in some other articles. Why? The dangers
are many. To name but a few scary possibilities:

  • Poor/dangerous suspension geometry
  • Overangled (broken) ball joints
  • Incorrectly routed (ripped) brake hoses

Now that we've said our piece on single-piston swaps, we can safely
move forward to the topic at hand: fixed caliper brakes. We aim to
discuss the various types used by Mother Mopar, then show you some
rebuild tricks and tweaks, and discuss new repro parts.

Three bodies, three disc brake systems

brakes2-2.jpg
Not counting the Imperial, Chrysler produced and sold three distinct platforms in the sixties. The smallest, the A-bodies
such as Valiants, Plymouth Dusters, Dodge Darts, early 'Cudas, etc., were offered with
Kelsey-Hayes fixed-caliper disc brakes from 1965 through 1972. These
brakes were an outgrowth of the Girling discs used successfully on
Scott Harvey's 1964 Monte Carlo Rally Valiant. They featured a grey
iron rotor measuring 11.04" diameter by 0.81 " thick, with cooling
vents, mounted (via pressed-in studs) to a forged steel hub with
replaceable tapered roller bearing cups (fig. 2.) Studs were 7/16" (R
and L,) and the bolt circle was 4-inch. Factory literature of the
period stated emphatically that these rotors were not to be machined
thinner, but replaced if the grooving made the rotor unuseable.
Research has uncovered the reason for that statement: the
factory had little confidence in the ability of the lathes then in use
to properly maintain runout and thickness variation specs, which are:

  • Minimum thickness: 0.750"
  • Maximum TI.R.: 0.0025
  • Max thickness variation (parallelism:) 0.0005"

Today, however, every garage has equipment capable of easily
maintaining those tolerances, so machining is now considered acceptable.

brakes3.jpg
The
calipers used with these rotors were two-piece units, with the halves
joined via two capscrews called "bridge bolts." Each half contained two
stainless-steel pistons measuring 1.636" diameter. Sealing rings were
square-section, and fitted in grooves in the housing. The section
design of these seals caused the seals to tend to return to their
natural shape after pressure was released, pulling the pistons, and,
therefore, the shoes, away from the rotor by a very small amount,
probably a few thousandths of an inch, a feature known as "seal
retraction." Fluid transfer between the halves was handled via a short
"jumper" length of 3/16" terne-coated steel tubing, double flared at
each end. Shoe and lining assemblies (pads) consisted of asbestos
linings bonded to the steel shoes, with wear-indicator tabs built in.
Their function was simplicity itself: once the lining was sufficiently
worn away, the tabs would contact the rotors and make a horrendous
noise, prompting the driver to seek service. The tabs contacted the
rotor outside of the normal wear area, so no damage was done by this
contact.

The mid-size Mopars, B-body cars such as Road Runners, Chargers, and
the like, probably needed disc brakes the most, with megapower 426 Hemi
and 440 powerplants being the rule rather than the exception, but, for
some reason, they received discs last-not until midyear, 1966. And,
even at that, the discs they finally got were, at least by some
measures, substandard.

DuraBrake has re-manufactured the Bendix rotors for the
B-bodies including the 1966-1969 Dodge Coronets and Chargers, Plymouth
Belvedere, Satellite, GTX, and Road Runner. This is the rotor only, for the two piece setup. Contact DuraBrake at 650-210-9315 x109.

B-body 4-piston discs, circa 1966-69, were manufactured by Bendix.
They used a rotor similar in design to the A-body K-H piece, measuring
11.19" by 0.875 thick, but, of course, using 1/2-inch studs and the big
car 4-inch bolt circle. Those dimensions are the problem! Although
B-bodies could weigh well over 4,000 pounds, and have a MGW of more
than 5,000 pounds (wagons), the brakes were only slightly larger than
the 3400-pound A-body units.

Although, at first glance, the Bendix setup appears to be similar to
the Kelsey Hayes deal, there are several significant differences. First
is piston design. Where the K-H setup uses straight pistons (with only
a single groove for the environmental seal,) the Bendix pistons use a
lip-type seal on the lower skirt, said seal moving with the piston
instead of being fixed in the bore as in the Kelsey design. Another
notable difference is the lack of a crossover tube on the Bendix setup;
in its place are two 0-ring type seals.

Last in the family of Mopar disc triplets are the Budd design used
on the large C-body cars from 1966 though '68. These cars were blessed
with 11.88 x .875" rotors, enough for the task at hand. The Budd design
utilized a unique caliper design, using a strange piston configuration
with a piloting nose to keep the otherwise short piston from becoming
cocked and jamming. The piston also had a bolt-on insulator pad with
dual functions: keeping brake heat away from the fluid, and noise
reduction. These brakes are seldom seen today, and very hard to get
parts for. For those reasons, we'll end our coverage of them with the
above description. [UPDATE, July 2007: DuraBrake (650-210-9315) has tooled up the Budd disc brakes for the C-bodies and has them in stock if necessary. They have the rotor only.]

Tweaks and Tuneups

The A-body K-H brakes are fairly straightforward to service. In
fact, lining replacement is about the easiest of any car on the road.
Simply remove the antirattle retainers, and force the pistons back in
the bores by using Chanellock type pliers on the pads. Once the pistons
are bottomed, the pads simply lift out the top, and the new ones drop
right in.

Caliper rebuilding is plagued by the usual syndrome: stuck pistons.
The factory method for removing them is to remove the calipers from the
car, split them apart, and use a special puller to free the pistons.
Aftermarket tool companies produced all manner of special pullers
for this job, but a much easier method is to leave the calipers on the
car, but remove the pads. Now, simply pump the brakes to use hydraulic
pressure to force the pistons free. If you use this method, just be
sure to keep the master cylinder topped off. Once all four (or eight)
are free, remove the calipers, split, and continue with the rebuild.
These calipers are pretty simple to do, needing no special tools
whatsoever other than maybe a small drill operated hone. We've had
satisfactory results many times by just cleaning the bores with
Scotch-Brite pads.

One trick that vastly eases boot installation is to
assemble the boot so its bottom lip is hanging beneath the piston. Now,
work the boot into the caliper groove, and simply push the piston into
place. This trick also works well on the larger, single-piston calipers.

As we mentioned, the rotors can safely be machined as long as the
specs of 0.0005" max thickness variation, 0.0025" max T.LR., and 0.750"
minimum thicknesses are maintained.

The Bendix setup is notably different. Pad replacement is by
unbolting the caliper and dropping the pads out "bottom." Due to the
unusual piston design, the pistons can usually be pushed back into the
bore with your fingers. This is of limited usefulness, as the
internal springs will just push them right back out. The procedure is
to simply push the new linings apart (with the same digital tools - your
fingers) as the caliper is remounted.

Bendix calipers rarely need rebuilding, due to the unusual, almost
barrel-shaped piston configuration. If a rebuild is needed, a special
factory piston-installing collar and boot-seating tool are helpful.
Nonetheless, with a little time, determination, and at least two small
plastic screwdrivers, they'll yield to reassembly. If your
calipers are extremely corroded, you should consider replacements. (See
the next section for more on that topic.)

Bendix rotors can also be resurfaced, with the same parallelism
(thickness variation) spec as the K-Hs. For some reason, though, Bendix
allows 0.005" TI.R., but adds the proviso that there should be no more
than 0.001 runout in any 30 degrees of rotation, and no more than three
reversals in a full turn. Minimum thickness is 0.816".

For both the Bendix and Kelsey designs, the best trick seems to be
placing a heavy coat of silicone grease in the bore and seal grooves,
and using silicone brake fluid. Especially in the prone-to-stick K-H
setup, the silicone will go a long way towards preventing future
headaches.

Parts is parts

brakes2.jpg
These brakes were
all made for Chrysler by outside vendors, so the aftermarket and
junk-yard may provide a richer source of parts than it might otherwise
appear. For example, the K-H A-body setup was also used on all pre-1968
Mustangs. The Bendix setup was also used on certain 1967-69 Buicks and
most 1965-70 AMC products.

Many car parts chains still carry pads, pistons, and
seals for these brakes. If you aren't so adventuresome, and desire
rebuilt calipers, these also aren't too hard to find. Even
stainless-sleeved units are out there. Pads are readily available, and we
even found some NOS gennie Mopar B-body ones at Goodmark Industries. If
you're going racing, you might want to search out a set of VeIveTouch
full-metallic pads, available from S.K. Wellman distributors nationwide.

Rotors have been the tough part. The A-body units have been
available both from Mopar and the aftermarket as recently as the
mid-1980s, so they aren't too tough to find, but those B-body Bendix
rotors have been in the same category as SuperBird wings, 1971 Cuda
grilles and 1967 GTX taillamp bezels-made of unobtainium. Luckily,
Goodmark saw the need, and actually tooled up to produce new rotors.
Unlike the originals, they are a one-piece unicast design, reducing the
runout-when-hot tendency. They also have reinforcing ribs to prevent
hub failures.

The Bendix setup, as mentioned above, doesn't use a crossover tube, but
it does use a small tube to connect the caliper to the flexible hose,
unlike the K-H setup where the hose screws directly into the caliper.
This length of tubing is, for some unknown reason, not flared with the
usual double flare. Instead, it uses an oddball ISO bubble flare. If
the tubing becomes damaged, or is heavily corroded, a new one can be
had from Year One as catalog number A0717 (a pair.)

Conclusion

The four-piston setups used in Chrysler products were solid
performers, with the exception that Bendix design was more prone to
fade than we'd like. For those, we'd recommend a set of custom-made
semimetallic, full-metallic, or carbon-metallic pads. Otherwise, all of
these brakes were totally dependable performers, requiring little more
than common sense and reasonable maintenance to keep you stopping well
into the next century.

More from Rick Ehrenberg

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