Whether you’re a tuner enthusiast looking to get your car track-ready or want to tweak the performance of your older muscle car or truck, ditching those drum brakes for discs should be one of the first mods you should consider. Drum brakes are easily damaged by heat, moisture and debris, they offer less-than-optimal stopping power, and often need regular adjustment. And, let’s face it, they look much better behind those awesome wheels than even nicely cleaned and painted drums can ever hope to look.
Classic muscle cars were equipped with drum brakes, except for a few special models that were equipped with front disc and rear drum brakes. But even most modern cars and trucks still come standard with drums on rear wheels because they are less expensive and the front brakes do most of the work anyway.
Front- and rear-brake assemblies are not interchangeable, so the conversion process for each does differ slightly. Below we’ll outline what’s required for each and what potential complications you can run into. The exact process is going to vary among different cars, but there are some basics that are the same no matter what make and model you’re working on.
Disc Brake Conversion Kits vs. Junkyarding
Like with most mods, if you’re simply looking to upgrade the brakes on an older car, hitting the junkyard for donor parts is often a cheaper alternative to aftermarket parts. Conversion kits can cost anywhere from a few hundred dollars to a few thousand with lower-end kits having simple flat rotors while the high-end kits have slotted or more aerated designs for better cooling and performance. But there’s also a reason why there are so many conversion kits on the market and why seasoned car builders and restorers often prefer the aftermarket route for this particular task. Once we started doing our research and considering all the variables for our project cars we quickly realized that trying to put together a brake system from scratch was going to involve a great deal of trial-fitting to get the combination just right – fine if you’ve got the time, which, what enthusiast does?
Depending on your car and what you’re trying to get out of your conversion, this is one instance where the aftermarket really comes to the rescue. They’ve done all the extensive legwork for you to put together a kit with parts that best fit your car.
Converting Rear Drums to Discs
Switching from rear drums to rear disc brakes on a RWD vehicle is probably the most common. The procedure may vary a bit depending on your kit but here are the basic steps:
- Block a front wheel front and back to keep the car from rolling.
- Loosen the lug nuts on both wheels.
- Jack the rear of the vehicle up and place jack stands under the frame or axles.
- Remove the differential cover or drain plug and drain the fluid.
- Disconnect the brake line to the wheel cylinders and parking brake cable.
- Remove the axles.
- Unbolt the drum brake backing plate and remove the whole drum assembly.
- Bolt on the disc brake backing plate.
- Reinstall the axles and differential cover.
- Hang the rotors.
- Install the brake pads and calipers.
- Connect the brake fluid line and emergency brake cables.
- Bleed the system.
- Rehang the wheels.
- Refill the differential.
- Raise the rear end off of the jack stands and lower the vehicle.
- Torque the wheels.
Some conversions won’t be this easy especially if you have an older and less popular chassis. One major factor you have to take into account is your parking brake system. In some cases your new brakes will be compatible with your existing parking brake system and you’ll simply reconnect your cables after performing the conversion while in other cases you may have to replace the entire thing.
Although your kit will have just about everything you need to install your new brakes, on some cars you may have to replace the axles to use disc brakes. And, you may find that the replacement axles are either too long, have too many (or not enough) splines, are too short, or are too thick. Some of the time, it’s going to be easier to just swap out the whole axle assembly, disc brakes and all. Doing this you may have to weld shock or strut mounts, but that’s much easier than swapping out the ring and pinion in the axle housing.
Converting Front Drums to Discs
This procedure is a little harder because you’re probably working on an older car and it may mean that you’ll have to do a bit more than just replacing the drum brakes. Again, there are some basic steps that will pretty much be the same no matter what you’re working on, but each make and model will have its own idiosyncrasies you need to watch out for:
- Set the parking brake and put the transmission in gear (manual trans) or park (automatics).
- Block one rear wheel front and back and loosen the lug nuts on the front wheels.
- Jack the front end up and place stands under the frame behind each wheel.
- Remove the wheels.
- Remove the brake drums.
- Clamp the brake line and remove it from the wheel cylinder.
- Disconnect the outer tie rod end (you’ll need a hammer and pickle fork).
- Remove the shock absorber.
- Attach a coil spring compressor tool.
- Place the jack under the lower ball joint.
- Remove the nuts from the upper and lower ball joints.
- Separate the steering knuckle from the control arms.
- Lower the jack enough to remove the steering knuckle.
- Now’s a great time to replace the ball joints.
- Install the new disc brake steering knuckle and torque the nuts.
- Remove the coil spring tool and the jack from under the control arm.
- Connect the outer tie rod end and torque the nut.
- Pack and install wheel bearings and grease seal.
- Install/hang the rotor.
- Attach the brake pads and hang the calipers.
- Reattach and unclamp the brake lines.
- Pop open the bleeder screw and allow the calipers to fill with fluid, refilling the master cylinder as needed.
- Bleed the system.
- Hang the wheels.
- Lower the car and torque the wheels.
- Set the toe using a tape measure.
- Get the front end aligned properly.
If you’re doing a conversion on a pre-70’s car, chances are you’ll also have to switch out the master cylinder including the booster, vacuum hose and proportioning valve. But there are kits for that too!
You’ll most likely have to tamper with suspension components so do your best to mark up how they were connected in the first place so you can get your alignment in the right ballpark and then get your wheels professionally aligned for long-lasting results.
Final Notes & Safety
- Wear safety glasses while performing this type of work. Trust me, brake fluid in the eye doesn’t feel good at all.
- Be careful with the brake fluid, it’ll ruin any paint it gets on.
- Properly dispose of the old brake fluid.
- Fully drain and flush the system. Why pump old fluid into new-ish calipers?
- When installing the new steering knuckle, you’ll probably need to jimmy with the coil spring to get it properly seated before putting the ball joint studs through the knuckle ball joint holes.
- If you’re doing a full four wheel drum to disc conversion, it’s important to remember that most of the braking force is applied at the front wheels. Because of this, you want smaller rotors and calipers in the rear than in the front. If you use brakes in the rear that are too big, you could end up locking them up every time you apply them.
While a drum to disc brake conversion takes patience, attention to detail and a good understanding of basic maintenance, as long as you know your calipers from your spindles, it’s a mod you can probably handle yourself.
Photo credit: digitizedchaos