Manufacturers started offering disc brakes for their one two punch of better braking performance coupled with fewer moving parts for assembly line simplicity. Drum brakes may sometimes be lighter overall but are far more complicated to install (both from an assembly line standpoint and from a service standpoint), and are more susceptible to brake fade, contamination, and thermal breakdown of the shoes, springs, and other parts. Whereas disc brakes have fewer moving parts, run cooler, and are less susceptible to brake fade. For this very reason manufacturers slowly adopted disc brakes as the standard front brake system on vehicles moving into the 1970s and beyond. Today you can update just about anything on four wheels to run front disc brakes (at a minimum) or even 4-wheel disc brakes thanks to companies like Speedway Motors, where hundreds of disc brake upgrade kits are available for everything from pre-war hot rods to muscle cars, and classic trucks.

We’ll start with drum brakes, as that is what many of you are considering replacing with modern disc brakes via a conversion kit of some sort. The drum brake system consists of a backing plate, which mounts the primary and secondary brake shoe linings, a hydraulic wheel cylinder, and mounting hardware/return springs that secure the brake shoes and wheel cylinder in place. The assembly is covered by a brake drum which is keyed to the wheels via the axles or hubs and wheel studs. When hydraulic pressure is applied via the brake pedal and master cylinder, the wheel cylinder’s internal pistons push outward on the brake shoes, which move outward and contacts the drum, applying friction force to slow the drum, which in turn slows the connected wheels.

Drum brakes certainly got the job done back in the day, but are well known for their issues, including retaining heat that can introduce brake fade, more complex assembly with more moving parts, brake “grabbing” when wet, and the need for regular manual cleaning of the drum brake assembly. Now consider today’s highway speeds, the increased performance we add to our classic muscle cars, hot rods, and pickup trucks, and it is easy to see why drum brakes simply are unsafe by today’s standards. See for yourself in this NHTSA report on the benefits of dual bowl master cylinders and upgrading drum brakes to disc!

While the drum brake applies outward force on the brake shoes to slow the brake drum, a disc brake system works more efficiently in a “C-clamp” manner by utilizing a caliper assembly with one or more pistons that is placed over the disc brake rotor (which is keyed to the wheels via the axle or hub, just like a drum brake). This clamping force is greater than that of what a drum brake can apply, and this is where the self-cleaning function comes into play, as the disc brake pads themselves scrape away old lining material, dirt, and debris to keep the brake rotor clean. The “open” nature of the disc brake system also means greater heat dissipation compared to the enclosed brake drum covering the drum brake components.

So many early muscle cars and certainly pre-war hot rods were built with drum brakes as the primary front braking system it is a solid bet if you pick up a project vehicle it’s still going to be rolling on drums (and they’ll quite possibly be seized up from sitting too!). Obviously, the first step will be to remove the old drum brake components. For the front brakes we are focusing on that means removing the drum with bearing hub, and then the backing plate with brake shoes, wheel cylinder, and hardware can usually be removed as a complete assembly. Disc brake kits require their own flexible brake hose that differs from a drum brake hose, so remove the old hose at the frame rail connection and at this point you should have a bare drum brake spindle to clean up and prepare.

Moving into the muscle car and classic truck drum to disc brake conversion it can quite often require replacing the drum brake spindle for a disc brake spindle. If this is the case our disc brake conversion kit will either include the required spindles or will provide details on where to source disc brake spindles for your conversion. However, we do offer several drum to disc brake conversion kits for muscle cars that retain the drum brake spindle as well, making the swap an easy one providing your spindles are good to go. Many of our replacement spindles are offered in a drop option, providing a 2- or 3-inch drop, which produces the lowered stance many want without affecting suspension ride quality and handling.