James Duff Ford Bronco Disc Brake Swap - Slow Your Steed
Increasing Our Stopping Distance
Disc brakes were not an option on the front of a Ford Bronco until the 75 model year, and they were never offered from the factory on the rear of a Bronco. Our Death Proof Bronco came with four-wheel drums that were adequate with the dinky stock tires, but after adding 35-inch Pit Bull Rockers we had to anticipate which way the Bronco was going to pull every time we hit the brakes, and stopping distances were on par with a loaded semi-truck. We added front disc brakes using factory parts, and they provided a vast improvement. Fast-forward to 2014. We have bumped our tire size up to 37-inch Pit Bull Rockers on 17-inch Allied Rock 8 beadlock rims, and all of a sudden our brakes seem marginal again.
We made a call to the Bronco experts at James Duff, who recommended a bolt-on rear disc brake conversion and proportioning valve for four-wheel discs. “My father originally developed a rear disc brake kit in the 70s,” Suzanne Duff explained. “But back then no one ran big enough tires to really justify the upgrade. He always seemed to be ahead of his time.”
We bolted the new rear brakes on in a day and after bleeding the system were enjoying stopping distances that are more akin to a sports car than a semi-truck. We even performed before-and-after braking tests from 60 to 0 mph to quantify the gains, and they were huge, shaving over a third off of our braking distances.
James Duff offers kits for both big-bearing and small-bearing housing ends. Each kit is completely bolt-on with brackets that allow the caliper to be positioned in different orientations to clear shock mounts or other suspension components.
We recently upgraded to 37-inch Pit Bull Rockers on 17-inch Allied steel beadlock rims. The additional weight and greater leverage from the taller tires was enough to overpower our previously marginal braking system.
Good riddance! Despite frequent rebuilding we could never get our drums to function properly. As a result, the front brakes were doing all of the work. We had broken multiple stub shafts recently and feel that the lack of rear brakes was a contributing factor with the front end trying to move the vehicle forward in 4WD while doing all of the stopping. The upgrade was well justified.
The supplied rotors are 11 9⁄16-inch vented units that come with the correct 5x51⁄2 bolt pattern. They are new and not redrilled from some other application with a different bolt pattern.
We also sourced a new proportioning valve from James Duff that bolts into the factory location. The new valve is configured to distribute the proper pressure to the new rear discs, which require more fluid that the drum brake wheel cylinders.
Oops. We reinstalled our Yukon axleshaft before installing the brake hardware and couldn’t get the bolts past the flange. The hardware has to go on before the axleshaft.
A variety of different width spacers are included to allow you to position the caliper accurately on the rotor on your specific truck. With a single piston caliper, the outside pad should be as close to the rotor as possible without making contact.
The calipers used in the James Duff kit are standard GM parts that are inexpensive and allow pads and other replacement parts to be purchased at any auto parts store around the country.
We chose calipers without emergency/parking brake capability to save on cost and complexity. Our experience with disc parking brakes has not been very good, so we intend to install a line lock instead.
We did have to make new brake lines to mate up to our calipers. The hard lines along the axlehousing were retained, but we added soft lines that tie in to the calipers and allow for some movement. With the bleed valve on the top the calipers do not have to be removed to bleed the brakes.
We performed before and after testing on a private road with some help from our friends. This allowed us to quantify the improvement from the rear discs brakes from James Duff (and was a lot of fun too).
|Braking From 60 to 0 MPH|
|Before (front factory disc/rear drum, ft): 192|
|After (front factory disc/rear James Duff disc, ft): 127|