Weld-on Rear Disc Brake Conversion

Rear discs are a desirable upgrade because they offer numerous advantages over the stock rear drum brakes. Discs are less susceptible to mud and dirt reducing their effectiveness, provide much more clamping power, can be more precisely modulated, are less prone to brake fade, work just as effectively in forward or reverse and they make servicing the brakes and the rear axle much simpler.

A weld-on rear disc conversion is very simple when it uses the stock Samurai front brake hardware. In building this rear axle, we used the stock front calipers, caliper mounts, brake hoses, and rotors.

Starting with a stock rear axle housing, we'll weld caliper mounts to the ends of the housing. The mounts will have a 2½" notch cut into them to allow them to fit over the axle tube and then slide over against the axle housing flange. Instead of cutting the notch in the center at the bottom, offset it to allow three out of the four bolt holes to be re-used, rather than just two out of the four as we did on this axle. You can then tip the mounts forward so that the backing plate bolts will fit through the mounts.

Welding of the caliper mounts to the housing must be done by someone knowing how to weld properly. If the housing is heated up too much, it will shrink and make installing the axles more difficult. Also, strong welds are a necessity for ensuring safety. Triple-check the alignment of the mounts before beginning to weld them, and make sure they are firmly clamped to the housing so that they don?t slip. After welding is complete, use a drill to extend the flange holes through the caliper mounts so that the backing plate can be bolted on.

The stock drum brake backing plates must be cut down to the size of the axle housing flange. Alternatively, you can use the OEM SJ-410 backing plates, which I had already installed on my axles previously, making the disc conversion even easier.

The next major step is making the axle-to-wheel adapter plates from a pair of Samurai brake drums. All this does is allow the 5-lug wheels to bolt to the 4-lug axle ends. You can hammer out the old studs and take the drums to a machine shop to have them cut on a lathe.

You'll also need to install longer front wheel studs, which are necessary to accommodate the additional thickness of the rotors.

The axles can then be reinstalled in the housing. Since the SJ-410 backing plates were designed to bolt to the flanges with another plate between them, I used a couple of washers on each bolt to properly space the backing plate from the housing. The bolts which pass through the caliper mounts will need to be longer than stock.

Next, the adapter plates can be bolted to the ends of the axles and the rotors bolted in place. With the rotor securely in place, the calipers can be fitted over the discs and bolted to the caliper mounts, using washers between the calipers and the mounts to properly align them on the discs.

Using the stock rear brake lines, a front brake hose can be installed between each caliper and the hard lines and the brake system can then be refilled and bled.

While an adjustable proportioning valve is not strictly necessary for a trail-only vehicle, a street-driven Samurai requires a proportioning valve to compensate for the increased stopping power of the rear discs. Premature rear lock-up will otherwise be a problem, especially on wet pavement. Spidertrax sells separately the same proportioning valve setup that is included in their brake line kits; we highly recommend installing one. Failure to do so puts not only your life, but also the lives of your passengers and other motorists in danger.

You should also plan on converting your vehicle from dual-diagonal split braking to front-rear split braking if required. Samurais having dual rear brake lines are 'dual-diagonal vehicles' and must be converted for safe braking when using rear discs. This is easily accomplished by swapping the position of two of the brake lines at the brake line header inside the passenger side of the frame at the front of the truck. See our tech article about installing the Spidertrax Brake Line Kit for details.

Before any high-speed testing, some gentle braking at low speeds in a safe area is a necessary precaution. If preliminary tests reveal no problems, gradually work your speed up and increase your braking pressure as you test the new brakes, keeping in mind that you will likely have used brand new brake pads and freshly turned rotors that may tend to 'grab'.