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Drum to Disc Brake Conversion Guide

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While every performance vehicle owner’s first thought is on making more power and going faster, the key to a well-balanced hot rod, muscle car, or race car, is having comparable levels of suspension and braking to support all that fun horsepower. When it comes to brake systems, we highly recommend a disc brake conversion kit. Upgrading your front drum brakes with a drum to disc brake conversion kit is at a minimum recommended for driving on today’s roads at modern speeds with the higher traffic counts we now must navigate. Better yet, updating your ride to 4-wheel disc brakes ensures you have the best braking possible. We have vehicle specific front and rear disc brake conversion kits, as well as universal bolt-on and weld-on drum to disc brake conversion kits for just about anything with four wheels and any performance application that will make your drum to disc brake conversion a breeze.

Why Should I upgrade to Disc Brakes?

Drum brakes were the prevalent braking system on vehicles for the first half of the 20th century. They worked (most of the time) for these lighter vehicles with low horsepower and slower road speeds of the time. However, once hot rodders began to ditch the original engines in their projects and repower them with higher horsepower V-8 engines, the original drum brakes showed their weaknesses. These include increased heat retention, brake fade, grabbing (especially when used in wet weather), and the constant cleaning and adjustment necessary to obtain optimum braking from them. A popular upgrade of the time was to increase the brake drum diameter and lining width from another application. It was even popular to find a drum conversion kit on the market. This may have helped initial brake application, but the larger drums still suffered from heat, brake fade, and all the other issues the stock drums suffered from. When you convert from drum brakes to disc brakes you solve all these issues.

Because a braking system turns a vehicle’s kinetic energy into thermal energy to be dispersed, having a way to quickly extract that heat from the braking system and keep the brakes cool is imperative to braking performance. Enter the disc brake assembly. No longer were the brake’s friction materials encased in a drum, but out in the open where air can keep them cooler. The exposed brake rotor friction surface, brake pads, and calipers, all helped to dissipate this heat more efficiently. Disc brakes are also much more effective in wet weather since the rotor can shed water quickly, unlike a drum where the water will stay inside, causing the friction material to become “grabby”. Furthermore, unless used at their extremes (such as road racing) disc brakes are much less prone to brake fade. Best of all, disc brakes are self-cleaning and self-adjusting and are simpler to service with fewer parts involved. All these benefits are the reason converting from drum to disc brakes have become so popular.

What is the Difference Between a Floating Caliper and a Fixed Caliper?

The most common brake caliper used by many OEs and in the typical disc brake conversion kit is the floating caliper. These calipers generally use a single large piston but can have two or three pistons as part of their design (see more on caliper pistons below). The piston is located on the inboard side of the brake rotor. They attach to the spindle or rear axle housing via a bracket that uses a sliding mechanism of some sort, either guide pins or machined mating grooves in the caliper body and mounting bracket. This allows the caliper to “float” on the mounting bracket so that when brake fluid pressure is applied to the caliper piston(s) the piston pushes against the inboard face of the brake rotor, forcing the caliper body inboard in the opposite direction. This action creates a clamping force between the brake pads and the rotor surfaces.

A fixed caliper is just what you think it is, a caliper fixed to its mounting bracket via bolts. The caliper is rigidly mounted to the bracket and does not move. As such, these calipers require pistons on both sides of the rotor surfaces to evenly apply braking pressure. At a minimum fixed calipers are usually 4-piston, but there are 6- and 8-piston calipers on the market, some with fixed piston sizes and others with varied piston sizes that help to offset brake pad taper by having a slightly increased clamping force on the rotor as it exits the caliper. You will find both styles of calipers available in the typical drum brakes to disc brakes conversion kit.

Now that we have described the two styles of calipers found in a typical drum to disc brake conversion, you are probably wondering which one is best for your application. For street use a floating caliper works great and obviously it will get the job done for mild performance use as well. Moving to a fixed caliper offers a few additional benefits, including a more rigid caliper to rotor relationship, increasing braking effectiveness and pedal feel. Now you don’t have the flex of a floating caliper arrangement causing a loss of braking effort. Secondly, a fixed caliper allows tighter wheel to brake system tolerances, as a floating caliper needs some “wiggle room” for its in and out movement during braking. However, due to the fixed mounting, installation takes a little more effort as you generally must shim the caliper to rotor dimensions to ensure correct brake pad to rotor air gap and proper brake pad wear. Fixed calipers also tend to be a little wider/beefier and can have external crossover lines (the fluid has to get to the other side of the caliper somehow) and this can cause issues with some suspension pieces and may require larger diameter wheels for clearance. Today’s argument is no longer drum vs disc brakes, but floating vs fixed calipers.

Are More Pistons in a Caliper Better?

Generally, yes, the more pistons the better in your disc brake calipers. If you compare a single piston caliper to the typical 4-piston, you will notice a couple of things. First, the 4-piston caliper, due to its smaller diameter pistons, utilizes a narrower brake pad. Since the pad is narrower, but longer, it usually has at least the same surface area of the single piston, if not more. Since the pad is narrower the caliper’s effective radius can be increased (moving the caliper outward from the center/hub of the rotor), which in turn increases the brake torque of the system. With a multi-piston caliper you will usually see a larger pad friction surface, which also increases braking effectiveness. The multi-piston caliper’s larger friction surface area translates into better, firmer, braking, increased heat dissipation, and longer pad life as well. Another advantage on a 4- or 6-piston fixed caliper is ease of brake pad servicing. Your typical single piston caliper is “U” shaped and requires full removal from the caliper bracket to access the brake pads. Most, but not all, fixed calipers have a large cotter pin or bolt with lock nut that allows easy removal of the pads from the top of the caliper for inspection and servicing needs.

Is Bigger Better When It Comes to Brake Rotors?

Like increasing your disc brake caliper’s piston count, increasing your brake rotor diameter helps with braking performance. A larger diameter rotor not only increases the braking surface area, but they also offer better thermal management. The large rotor is also thicker with longer internal cooling vanes, which all come together to provide increased thermal transfer. Remember that brake torque we mentioned earlier? Well, increasing rotor size moves the caliper further away from the center/hub and adds to that brake torque efficiency. Using a disc brake conversion kit with multiple pistons in a fixed caliper, paired with a larger diameter rotor, will always provide the best braking solution. That said, often wheel choices, suspension components, and even the type of spindle or axle you are fitting your disc brake upgrade to may limit your disc brake conversion kit choices. When you consider a disc brake conversion kit, a basic kit with 11-inch rotors will require a 15-inch wheel. As you go up in rotor size so must your wheel size—typically one inch in wheel diameter for each inch in rotor size. For example, to use a 13-inch rotor with a fixed caliper you will need a 17-inch wheel at a minimum.

Updated by Mark Houlahan