Our '70 Duster originally...
Our '70 Duster originally came with 10-inch drums all around-barely adequate 30 years ago, and downright scary in a car with 350 hp at the rear wheels. Considering that serviceable rear drums are hard to find, and our pre-'73 A-Body had the oddball 5 on 4-inch wheel bolt pattern, a rear brake upgrade was high on our list.
In the old days when trucks were for work and musclecars rolled out of Detroit assembly lines, disc brakes were touted as an "upgrade." Salesmen would proudly declare, "...and this baby's got front discs." Today, salesmen key on airbags and cup holders, cars have discs at all four corners, and no one gives it a thought-except those of us riding around in 30-year-old American iron. Disc brakes provide more positive mechanical action, respond linearly to pedal effort, dissipate heat faster, and just plain stop the car more quickly and with fewer quirks than drum brakes. While Mopars could be had with optional front disc brakes, four-wheel discs were the realm of exotica, found only on sportscars like Corvettes or high-end imports such as Aston Martins and Jags. No, it wasn't the territory of Coronets and Dusters.
Making up for the low-grade factory braking hardware is a simple proposition today. The parts to upgrade any corner of a classic Mopar to disc brakes are readily available in kit form. Unlike some of the older conversions, which adapted racing components to Mopar applications, these modern kits utilize durable OE quality components, with such niceties as parking brakes, weather seals, and off-the-shelf availability of replacement pads. Our '70 Duster, sadly, was fitted with 10-inch drums all around. Hard braking provoked poor directional stability, and braking capacity soon degenerated as a result of brake fade-safe enough for low-speed commuting, but not up to the job of halting a high-powered hot rod.
We found that Stainless Steel Brakes Corporation (SSBC) offers bolt-in conversion kits to upgrade drum brakes to discs at either end. The promise of improved braking captivated our interest. We like the idea of retaining our original front spindles for an easy installation, as well as the double-drilled wheel bolt pattern, which would allow an upgrade from the Duster's small bolt pattern.
While adding discs to the front end is a major step forward, we wanted to ditch the puny 10x1 3/4-inch A-Body rear drums at the same time. We ordered SSBC's basic Mopar disc brake conversion kits for the front and rear of the Duster. Beyond the basic kit, SSBC offers a number of optional upgrades, including lightweight high-capacity aluminum calipers and slotted rotors. Installing the system proved easy and with no surprises, which is a good thing. A better thing was the improved braking performance. With the stock drums, which we had fully rebuilt, slowing the Duster down at the track from 110 mph was a handful. There was no telling which way it would want to go, but it was certainly not straight. With four wheel discs, the stops became controlled and predictable. Unlike single-purpose lightweight drag brakes, off the strip, the SSBC kit has the capacity and durability to deliver the goods under "performance street" duty. This was definitely the dope for our dual-purpose Duster.
SSBC's rear disc brake conversion...
SSBC's rear disc brake conversion comes as a complete bolt-in kit, including the mounts and hoses, 11-inch vented one-piece rotors, and single-piston calipers with parking brake provisions. The rotors are double-drilled to accept either the stock pre-'73 A-Body's small wheel bolt pattern or the more common 5 on 4-1/2 inch bolt pattern. Swapping to the big bolt pattern requires either custom axle shafts or precision machining modifications of the stockers. Since wheel choice is limited with the small bolt pattern, our plan was to upgrade to the big bolt pattern at the same time as the brake swap.
Removing the brakes requires...
Removing the brakes requires pulling the axle shafts. On an 8 3/4 rear, as our Duster was equipped, the axle just unbolts at the bearing retainer and slides out. The 8 1/4- or 9 1/4-inch rears require opening the differential cover and pulling the differential gears to remove the axle retaining C-clips.
Slide the axle out, supporting...
Slide the axle out, supporting it so that the rough shaft doesn't drag across the inner axle seal.
The most troublesome part...
The most troublesome part of removing the stock drum brakes can be disconnecting the parking brake cable. The backing plates have to be stripped of the brake shoes. Slip a small hose clamp over the loose end of the cable to compress the locking barbs where the cable goes through the backing plate. Tightening the clamp will unlock the cable.
The axle housing's end studs...
The axle housing's end studs need to be knocked out. Swap them with the longer replacements in the kit.
Since we were changing to...
Since we were changing to the big bolt pattern, we ordered a set of Moser axles. With track time and running slicks in the cards, it's a worthwhile upgrade.
The caliper adapter goes over...
The caliper adapter goes over the longer housing end bolts. Insert the caliper bracket bolts into the adapter brackets before bolting them in, since they won't clear the axle shaft flange once the adapters are in place.
Next, install the provided...
Next, install the provided spacers, the dust shields, and the caliper bracket.
Slip the rotor in place and...
Slip the rotor in place and bolt the caliper to its mounting bracket. Check the alignment of the caliper to the rotor. The caliper should be centered over the rotor. If it's not, correct the alignment with shims.
Install the pads, the supplied...
Install the pads, the supplied brake lines, connect the stock parking brake, and the job is done.
Here's something you won't...
Here's something you won't see in any car built in the last decade-front drums. Pop the dust covers, pull the cotter pin, unscrew the spindle nut, and the drum comes off.
Remove the four bolts which...
Remove the four bolts which secure the drum to the spindle and the entire brake assembly comes off as a unit.
The lower rear bolt actually...
The lower rear bolt actually threads into the spindle, while the other three bolts just slide through and are retained by the nuts. For the conversion, the threads in this hole need to be removed by drilling with a 1/2-inch bit.
The beefy caliper adapter...
The beefy caliper adapter is threaded, and receives the bolts from the rear to attach solidly to the spindle.
SSBC's front kit comes complete...
SSBC's front kit comes complete with new wheel bearings. Make sure they are properly packed with quality disc-brake wheel-bearing grease.
The front rotor, as with the...
The front rotor, as with the rear, is a ventilated 11-inch piece with an integral hub. It fits onto the stock drum brake spindle with a machined spacer installed behind it.
A large four-piston fixed...
A large four-piston fixed iron caliper is standard in SSBC's conversion kit. Optional upgrades include their "Force 10" aluminum calipers. The pads slip in easily from the top.
Connecting the supplied hose...
Connecting the supplied hose to the stock retainer bracket required enlarging the mounting hole to fit the hose end.
Installing the SSBC discs...
Installing the SSBC discs turned out to be a quick and simple swap.
The small drum brake master...
The small drum brake master cylinder should be swapped for the larger SSBC replacement. Disconnect the pushrod at the pedal (manual brake cars only). Unhook the lines, unbolt it, and it's out.
The replacement cylinder is...
The replacement cylinder is much larger and familiar-looking.
To tune the system, SSBC supplies...
To tune the system, SSBC supplies an adjustable proportioning valve. It adjusts to vary the amount of pressure decrease to the rear brakes to prevent premature rear brake lock. Plumb it at the rear brake outlet of the stock combination valve and dial it in so that the rear brakes do not lock before the fronts.