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

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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 

Chrysler brake rotorNot 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.

brake caliper diagramThe 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

brake rotorsThese 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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