Disc Brake Upgrade

Converting from drum brake to disc on your old car has several advantages. If you're thinking of adding horsepower, it's a good idea to have more stopping power. Disc brakes shed heat much faster, which improves repeated braking performance, and disc brakes have less moving parts than drums and they don't require any periodic adjustment. Also, when disc rotors get wet, they dry off much quicker than drums do.

drum to disc brake upgrade

In addition to the safety and performance improvements, replacing drums with discs will also allow for a wider selection of wheels to choose from, as well as a larger selection of suspension mods. If you drive your old car more than 1,000 miles a year (or pull a boat), relying on 50-year-old brakes may not be a good idea. Ultimately, it makes your old car safer and more enjoyable to drive.

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Single-Reservoir vs Dual-Reservoir Master Cylinder

Many American cars built before mid-sixties have a single master cylinder. In this system, if you experience a brake line failure you lose all of your braking capacity! Most disc brake kits include a later-style master, so converting from drum to disc will automatically give you the safer dual master cylinder.

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Swapping to a set of front disc brakes is a relatively simple job, one that a weekend mechanic could accomplish with hand tools. There are two options to choose from when converting front manual drum brakes to power discs. You can either scrounge up good used parts from a donor car, or buy an aftermarket brake conversion kit.

GM A-Body Disc Brake Conversion

For GM A-body cars, which include the 1964-1972 Chevelle and Monte Carlo, Pontiac Lemans and GTO, Olds Cutlass and 4-4-2, and Buick Skylark, a disc brake swap is common. This is because all those years and models shared the same brakes and suspension parts, so you can swap the later 1968-1972 factory discs to the earlier, drum-equipped models. Keep in mind that you'll need at least 15" wheels in order to use discs on these early cars. The calipers will hit the inside of the smaller 14" wheel.

drum to disc conversion kit

Swap 68-72 A-Body Brakes

Thirty years ago, it was cheap and easy to find the later A-body disc parts, but the value of original classic cars makes them expensive and hard to find today. The parts needed are the two front calipers, disc brake spindles, backing plates, and brake hose brackets. Unless the old rotors are in very good shape, buy new ones. Never re-use old rubber brake hoses.

F-Body Spindle Swap

Another low-buck way to convert from drum to disc on your A-body car is to bolt on spindles and calipers from a 1970-1981 Camaro and Firebird (F-body). This swap can actually improve front end geometry, but you must shim the original control arm about an inch to bring the front end into alignment. The stock A-Body upper and lower control arms can be re-used, but the ball joint hole and bolt holes on the lower control arms need to be widened slightly to accommodate the new ball joints. Again, you'll need at least 15-inch wheels in order to use discs on those early models. The larger 11" Rotors will fit on 1964-1972 GM A Bodies, 1967-1969 GM F Bodies, and 1968-1974 GM X Bodies.

Manual Disc to Power Disc Brakes

All 1964-1966 A-bodies came from the factory with a single-reservoir master cylinder. In 1967, GM upgraded to a safer dual-reservoir master cylinder. You could run manual disc brakes, but for disc brakes to operate efficiently, they need a lot more line pressure than drums do. In other words, a stock drum-brake master cylinder does not have the added volume of brake fluid needed to operate disc brake calipers effectively.

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Adding Power Brakes

Power brakes give much improved stopping performance. The power booster adds pressure, so your foot doesn't have to! Manual to power brake conversion components include a dual-reservoir master cylinder, power brake booster and proportioning valve.

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Brake Line Fabrication

Do NOT assume that your existing brake lines will work! This includes the brake line from master cylinder to the frame mount fitting and the line that runs from left front to right front. In all likelihood, one or more lines will need to be replaced.

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Parts Needed For Disc Brake Swap

  • LH Spindle
  • RH Spindle
  • LH Caliper
  • RH Caliper
  • LH Backing Plate
  • RH Backing Plate
  • Brake Pads (set)
  • Rotors (2)
  • Brake Hoses (2)
  • LH Brake Hose Bracket
  • RH Brake Hose Bracket
  • Inner Wheel Bearings (2)
  • Outer Wheel Bearings (2)
  • Wheel Bearing Seals (2)
  • Master Cylinder
  • Power Brake Booster

Disc Brake Conversion Kits

With a good aftermarket brake kit, the parts-gathering has been done for you, and the conversion is a fairly simple weekend operation. Drum to disc conversion kits range in price from $300 and up. Kits generally include calipers, pads, rotors, hoses, bearing and hardware kits, caliper mounting brackets, backing plates (most kits) and spindles (when changing spindles is necessary). Manual disc conversion kits contain the same components as the drum-to-disc conversion kit, but also include a master cylinder, power brake booster and proportioning valve.

drum to disc conversion kit

Problems With Aftermarket Brake Kits

All over the internet forums, stories abound of frustrated restorers struggling with brake lines that don't fit, brakes that won't bleed, and when they call the company's tech-line, the techs can't answer their questions!

Be cautious when buying kits sold as "universal". Some of the cheaper kits don't include all parts needed, like the disc-brake backing plates. Stay away from companies with a "No Return" policy. Once you bolt it on you can't return it -- how do we know it will work if we don't bolt it on? Sometimes a disc brake spindle/rotor combination will place your wheel 3/4" outboard of where the drum-equipped wheel was. Instead of wasting hours of time and countless headaches, look for a known and trusted brand.

Rear Brake Conversion Kits

Before you add rear disc brakes, do your homework - you could end up with a car that stops worse than it did before. If you're running the stock-size 14" or 15" inch wheels, a front disc/rear drum setup is all you really need for street use. A rear disc conversion should only be considered if have substantially increased horsepower, or you've installed 17" or 18" tires. Oversize wheels and tires may also rub inner fender-wells, or may bottom out over a speed-bump or pothole.

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