We were standing around one day staring at an '04 Viper on the showroom floor, when the thought crossed our mind that just maybe those big honking disc brake calipers could be shoehorned onto our '65 Coronet. It was a short trip from the showroom floor to the parts counter, so we purchased a set of the calipers and hauled them home to see if we could make them work. Surprisingly enough, we were able to fit the big Viper binders onto our early B-Body without too much work.
Big CalipersBrembo is the OEM supplier for the calipers on the current Vipers, as well as the supplier for brake systems for many Porsches and Ferraris. These Brembo-sourced calipers are a four-piston design like the old KH and Bendix units used on Mopars back in the '60s, but these new Viper calipers are made from aluminum and are physically much larger than anything Ma Mopar ever used. Also, the Viper calipers use a radial mounting scheme that is much more rigid than the ear-type mounts that the Chrysler engineers used to use. Even though it is a lot larger, the fully loaded Viper caliper weighs basically the same as the stock cast-iron sliding caliper.
The Viper caliper, like most modern high-performance calipers, uses a differential piston design to keep the pads from wearing in a taper pattern. In these calipers, the leading piston is 40 mm in diameter, while the trailing piston is 44 mm. Due to this differential piston design, the calipers cannot be swapped from side to side on the car. These calipers are designed to be hung at the rear of the steering knuckle, but they could be front hung if the bleed screws and crossover lines were swapped. Since there wasn't an issue with rear hanging the calipers, we just followed the factory recommendation.
You might assume that calipers this nice would be really expensive, but that just isn't true. The Viper calipers can be purchased for around $250 each from a local Dodge dealer. That might sound like a lot to someone who isn't familiar with high-end brake systems, but it is actually a very fair price for this quality of caliper. Brembo calipers are as good as they get, and, at this price, they're cheaper than many of the lower-end brands.
Tall Knuckles, Trick Control ArmsThere has been a bit of a controversy over the years regarding which disc brake knuckle to use on a musclecar Mopar when updating to disc brakes. The disc knuckle from the '73-'76 A-Body cars has the same height as the existing drum knuckle, so that seems to be the obvious one to use, but it is also getting hard to find since those cars were only made for four years and have been out of production for 30 years.
Sometime ago, people started to suggest the use of the easier-to-find, but slightly taller knuckle off the FMJ-body cars. One problem that was pointed out is the slightly taller FMJ knuckle could possibly cause the upper ball joint to go beyond the designed travel limits at full suspension travel. The debate has raged every since and is a popular (and often heated) topic on the many Mopar Internet forums. Much to our surprise, in conducting some research for this article, we came across a solution to the tall knuckle concerns that some may have. It turns out that Dick Ross at Firm Feel Inc. (FFI) recently started to build tubular upper control arms that are designed to work with the taller FMJ knuckles. These FFI control arms have the ball joint socket installed on a slight angle to reduce the possibility of over-angling at full travel.
As soon as we discovered these new arms, we called FFI and ordered a set for our B-Body, complete with custom gold powdercoating. These tubular a-arms will provide more improved caster adjustability than the stock setup; they are slightly lighter than the stock units and more rigid. They also come complete with new ball joints and bushings already installed. As anyone who has tried to unscrew a set of 30-year-old ball joints out of some rusty a-arms can tell you, new is a very nice thing.
Big Rotors
The Viper calipers are designed to work with a rotor that is 1.250-inches thick and at least 13 inches in diameter. The rotor that comes on the Viper would have been a nice one to use, but for some strange reason Dodge engineers used a six-lug design on the Viper. That screwball design ruined any chance of retro-fitting the Viper rotors (or wheels) to our five-lug vehicle, so we went hunting for a suitable replacement. We ended up talking with Cass Eslick from Quality Body Shop in Polson, Montana. Cass is a Baer dealer, as well as a long-time Mopar guy, and he was able to find a set of rotors from Baer that worked. Cass was in the process of installing a big set of brakes on his A-Body at the same time that we were working on this project, so we joined forces and developed some parts together.
The Baer rotors that Cass found for this project are 13.15 inches in diameter and 1.250 inches thick. They are Baer PN 6920300 for the right side, and PN 6910300 for the left side. These are bare rotors, so if you order this part number you'll also need the correct hats and mounting hardware. Baer doesn't sell a hat that works for this application right out of the box, so we had to take Baer PN 6140072, redrill it for a 5x4.50 bolt pattern and then open up the center register diameter. The Baer rotors complete with hat section weigh 18.5 pounds each. When combined with the custom hubs that we built, the total weight per corner is 23 pounds. this setup is a little lighter than the factory 11.75 diameter rotor that weighs 26 pounds.
Selecting a hat takes a little bit of thinking since you want the rotor back far enough from the hub face so that the caliper will clear the wheels, but you don't want it so far back that it hits anything. Measure twice and fabricate once.
Custom Hubs And Caliper Adapters
The calipers are box stock from the local Dodge dealer, and the rotors are right out of Baer's catalog, but when it came time to bolt it all together we needed some custom parts, such as the hubs to mount the rotors on and a bracket to hang the caliper from.
The hub was definitely the most difficult part to develop since it is a very key part that has many critical dimensions. But this is the golden age of CNC machining equipment, so we knew that once we had a design in hand, getting the parts built wouldn't be an issue.
Designing a part such as a custom hub isn't really too difficult if you just follow a methodical approach. For instance, the bearing sizes and locations need to be the same as the stock hub, and it is a good idea to reuse the factory oil seal, as well as the factory dust cap. You really want the center of the tire to be in the factory location or else you'll have some issues. And you want the hub to be strong enough to deal with your average pot-hole-infested freeway. Once you crank all of those things together on the drawing board, you will end up with something that looks a lot like a drum brake hub, but just a little thicker.
We used 7075-T6 aluminum alloy for the hubs since it is both strong and light, but cold rolled steel could also be used for a street driven vehicle. We did the design in a $150 CAD system called MasterCam that runs on a desktop PC. Those CAD files were taken to a shop that has a CNC lathe, and they turned out the hubs for us in just a few days from some 6-inch diameter billet. Once the machine work was finished, we had the hubs anodized black, and pressed in the bearing races and the ARP lug bolts.
Once the hubs were finished, we needed to create a pair of brackets that would mount the Viper calipers to the late-model knuckles. The Viper caliper radial mounting system uses 12mm bolts running through the caliper, so an L-shaped bracket is required to attach to the knuckles. We inputed our measurements in the CAD system, and had a machine shop whittle up the adapters from a bar of 416-alloy stainless steel. We chose stainless steel for this application since it is rigid and has excellent corrosion resistance.
Big Wheels
The only thing that is going to clear a big caliper hanging on a 13.15-inch diameter rotor is a 17-inch or bigger rim. There are a lot of 17-inch rims on the market, but we've found the factory Mustang rims are hard to beat for the buck. Mustang rims are typically 17x8 with 5.72-inch backspacing, so they'll usually require some type of spacer to work on a Mopar. But we knew that in advance, and so we designed our hubs to accept a spacer without losing the center register for the wheel.
The Mustang rims are typically designed to have a lot of caliper clearance built into them, so they should clear a big four-piston caliper, such as the Viper unit. But this area is something that always needs to be checked and double-checked. In our case we designed everything to fit under a set of the five-spoke Mustang GT rims. These rims are often referred to as Bullitt rims because they look like the rims used on the Mustang in that infamous car chase.
The Bullitt rims are Ford PN M-1007-J178, and they fit just fine over these 13.15 rotors and Viper calipers. We also checked the '99 Cobra rim (PN M-1007-G178), and the '98 Cobra rim, (PN M-1007-D178), and they both fit. So there are at least three choices right out of the Ford Racing catalog that fit, and odds are that many other rims will also clear these big calipers.
Wrap Up
This obviously isn't a typical article where we bolt on a collection of parts from a vendor and report on the results. Rather, this is more of an "old school" article where we had to build some of the parts ourselves. Or to be more precise, we designed some special parts, and then had a professional machinist build them for us. But this really isn't much different than if you take your car in for a custom interior or some custom bodywork. In our case, we used a PC-based, computer-aided drawing package in order to get the dimensions correct, but a good machine shop would also be able to work from a full set of paper drawings if that is all that you had available to you.
We spent a fair amount of time poring over vendor catalogs looking for the magic combination of parts that could be combined to make a safe, yet economical, big brake kit. There isn't a commercially available kit that uses the late-model Viper caliper, but we really wanted that visual impact on our car. Now that we've done it, maybe someone will step into the marketplace with a kit like this. If not, I guess we have a one-of-one '65 Dodge Coronet.
Editor's Note:
Andy Finkbeiner, who designed the custom parts used in this article, is a professional engineer who has many years of experience in the area of hot-rod brake-system design and fabrication. We ran this article to showcase the Viper brake swap since we felt it would be of interest to many readers. However, unless you have the skills, experience, and capabilities to do your own brake-system design, you shouldn't take on a project like this. After all, we need to keep as many Mopar Muscle readers healthy and happy as possible.
