Weld-on Rear Disc Brake Conversion

Nov. 01, 2005 By ORC STAFF
Rear disc brakes are a popular upgrade for many vehicles, including the Suzuki Samurai. Spidertrax sells a bolt-on rear disc conversion kit, but building your own rear disc conversion is not as difficult as it might seem.

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'.


Initially, the new brakes were quite grabby as the new pads and rotor surfaces began to wear in. Very quickly, the new brakes ran in and began to work extremely well. In addition to providing a significant increase in braking power, modulation of the brakes under threshold braking is much more precise. Braking strength on each rear wheel is now equal, a far cry from the old rear drums. On-road, the rear discs make a very welcome improvement in the Samurai?s braking ability, more than making up for larger tires.

Off-road, the discs are again a blessing. In addition to a great increase in modulation capability on slippery surfaces, they are also unaffected by water and dirt. The biggest improvement of all, though, is the ability to back down a steep, slippery surface in 2wd and have control of the steering and speed. With the old rear drum brakes? ineffectiveness in reverse, backing down a steep hill unloaded the front wheels, causing them to lock up and thus losing any control of the speed of descent and steering. On several occasions I had close calls because of this braking problem. The disc brakes passed this definitive test with flying colors.

One other important benefit of this rear disc conversion is the simplification of maintenance on the rear axle. Without the drum brakes in the way, removing an axle takes no more than 10 minutes. As with an SJ-410 backing plate conversion for the drum brakes, carrying spare axles on the trail is much more compact without the huge Samurai backing plates. Changing an axle is now simpler than with a backing plate conversion alone. Brake pads should last much longer than the old drum brake shoes and the rear brakes should now be a very low maintenance item.

The biggest drawback to a rear disc conversion is the lack of a parking brake. The easiest solution is the use of either an SJ-410 transfer case mounted drum parking brake or Spidertrax? transfer case mounted disc parking brake. Without a parking brake, it is recommended that whenever the vehicle is left unattended, the engine is shut off with the transfer case left in low range and the transmission in first gear.

If a weld-on rear disc conversion isn?t for you, Spidertrax? bolt-on disc conversion kit provides all the same benefits without the welding. Or contact Chris Minerich?the technical advisor for this article? who can build a modified rear housing for you and supply the other necessary parts.

You will note that we also added a truss and skid plates to the rear axle housing to prepare it for off-road abuse. While not a necessary step for this conversion, armoring and strengthening the axle tube makes sense while you have it removed from the vehicle. Chris can also truss the axle for you.

Off-Road.com Newsletter
Join our Weekly Newsletter to get the latest off-road news, reviews, events, and alerts!