Fox Body Mustang Rear Disc Brake Conversion

Fox Body Mustang Rear Disc Brake Conversion

Last Updated December 19, 2023 | Kevin Brent

Many Fox Body Mustangs need braking system upgrades to meet modern performance and safety standards. Several Fox Body models came equipped with rear drum brakes that don't quite match the efficiency and responsiveness of disc brakes. Converting the rear braking system from drum to disc brakes is one of the most impactful Fox Body upgrades. This conversion helps enhance the car's stopping power, overall handling, and stability.

Check out our step-by-step instructions below for a comprehensive Fox Body Mustang rear disc brake conversion guide. We'll cover everything from the essential tools and components required, to detailed instructions on the removal of the old drum brakes and the installation of the new disc system.

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Tools Needed:

  • Wide Socket Set
  • Pry Bar
  • Scrapers
  • Hammer
  • Jack and Jack Stands
  • Wrenches & Pipe Wrenches
  • Brake Line Cutting Tool
  • Flaring Tool
  • Torque Wrench
  • Drum Brake Tools
  • Needle Nose Pliers
  • Disc Brake Quiet
  • White Lithium Grease
  • Vise on a Secure Table
  • Drip Pan for Gear Oil and Brake Fluid
  • Can of Bolt Loosener
  • Power Tools, especially an Air Ratchet, are helpful

Fox Body Mustang Rear Disc Brake Conversion Install

For this install, we used a 1987-1992 Mustang rear drum to disc brake conversion kit that applies to 4 lug axles and fits all four-cylinder and eight-cylinder Fox Body Mustang models. The kit you use may be slightly different, so make sure it matches your Mustang's year and model. Most aftermarket kits come with all required hardware and a master cylinder included.

Make sure you extensively test your converted brakes before using them on the road. They are an incredibly important safety feature on your Mustang so they need to work properly. If you're not comfortable completing a technical install, it's always an option to bring the kit to a mechanic and have it installed for you.

Step 1: Remove Drums and Brake Shoes

Use a jack to raise your Mustang and support it with jack stands on all four corners.

Remove your Mustang's wheels, then remove the drums and brake shoes. You may need to use a hammer to remove the drums.

Removing Classic Mustang drums and brake shoes

Step 2: Remove Differential Cover

Remove the Mustang differential cover and drain the gear oil. After removing the bolts on the differential cover, tap a pry bar or scraper in between the cover and the differential to separate them and break the seal. Keep one bolt threaded halfway until the differential is completely drained. After the fluid is drained, remove the remaining bolt and set the differential cover aside.

Removing Classic Mustang differential cover

Step 3: Remove Differential Pin

Locate the differential pin and retaining bolt. Remove the bolt and the pin should drop out. To keep the gear from spinning, use a pry bar when you remove the bolt. Be careful to not let the bolt or pin fall into the drain pan.

Removing Classic Mustang differential pin

Step 4: Remove Axle C-Clips

After you remove the differential pin, push the axle shafts inward about 1/2 inch until you can't move them any further. You should see the C-clips that retain the axle. Remove the clips with a pair of needle nose pliers.

Removing Classic Mustang axle c-clips

Step 5: Slide the Axle Out of the Differential

Slide the Mustang axles out of the differential and set them aside.

Removing Classic Mustang axle from differential

Step 6: Remove Stock Brake Line

Remove the brake line from the wheel cylinder. If your brake line is seized, you may need to cut it. The new brake lines will need to be cut in later steps.

Removing Classic Mustang stock brake line

Step 7: Remove Brake Drum Backing Plate

Remove the backing plate for the Mustang brake drums. You may need to spray penetrating fluid on the bolts if they have rust damage. Once the bolts are removed, let the plate hang from the parking brake cable.

Removing Classic Mustang brake drum backing plate

Step 8: Install New Splash Shield

Attach the supplied splash shield to the new brake drum backing plate.

Installing Classic Mustang splash shield

Step 9: Install New Backing Plate

Install the new backing plate with the supplied 14mm bolts. Make sure the brake caliper is mounted towards the back.

Installing New Classic Mustang backing plate

Step 10: Reinstall Clips and Retaining Bolt

Reinsert the axles, and reinstall the axle C-clips, then pull the axles out. They should not move out more than an inch. Reinstall the pin and the retaining bolt.

Reinstalling Classic Mustang differential clips and retaining bolt

Step 11: Reseal Differential cover

Clean off the old gasket material on the differential and cover pan. After the old gasket is clean, apply new sealant or a new differential cover gasket and re-bolt the cover to the differential.

Resealing Classic Mustang differential cover

Step 12: Add New Brake Rotor to Axle

Put the new Mustang brake rotor on the axle, then bolt it down so it won't wobble. If your lug nuts are not deep enough, use a 1/2 inch socket to fill the gap.

Adding new Classic Mustang brake rotors

Step 13: Connect Caliper to Backing Plate

Install the caliper to the backing plate. You might need to install shims in between the caliper and the backing plate so the parts align. Once everything lines up, torque the supplied bolts to 80 lb/ft. Make sure that the rotor turns around completely.

Connecting Classic Mustang caliper to backing plate

Step 14: Apply Disc Brake to Brake Pads

Remove the caliper from the caliper bracket. Apply disc brake quiet to the back of the brake pads.

Applying Classic Mustang disc brake to brake pad

Step 15: Install Brake Pads

Apply some white lithium grease to the caliper bracket where the brake pads will rest, then install the pads and reinstall the caliper back on the bracket.

Installing new Classic Mustang brake pads

Step 16: Install Banjo Fitting

Install the supplied banjo fitting using 2 copper washers on each side, then torque to 25 lb/ft. Install the line included in the hardware kit. You may need to bend the line so it fits correctly.

Installing Classic Mustang banjo fitting

Step 17: Cut and Connect New Brake Lines

Bend the Mustang brake hose so that the two coupling ends are facing away from each other. Then, cut the brake lines down further and install a compression fitting, along with a bit of the new line. Use a tool to flare out the end of the line or try bending the existing line. Use a brass fitting to connect the lines.

Reconnecting Classic Mustang brake lines

Step 18: Remove Old Master Cylinder and Lines

Remove the old master cylinder and the lines connecting it to the distribution valve. Unbolt the two nuts from the brake booster. Remove the brake line from under the master cylinder, then remove the brake lines from the top of the distribution valve. If they're seized, remove them from the side of the master cylinder, then cut the line and use a socket to remove it. After the lines are off, remove the master cylinder. You can dump out the remaining brake fluid.

Fox Body Mustang brake master cylinder lines

Step 19: Connect New Master Cylinder

Secure the new master cylinder in a vise, then install the hoses provided and loop them around to the reservoir. Fill the reservoir. Then, use a wooden or plastic dowel, and push on the master cylinder until the air bubbles completely disappear. Do this 5 to 10 more times after the last air bubble disappears.

Place the new master cylinder on the Mustang brake booster and bolt it down using the factory nuts. Install the new lines to the master cylinder, starting with the back one first, and bend them into position to connect to the distribution valve. Don't tighten them down until they are all in position. The line that went into the bottom of the master cylinder will go in the bottom of the brass 3-way T fitting. Make sure the lines are not too close to the exhaust.

Fox Body Mustang brake master cylinder

Step 20: Remove Parking Brake Cables

To remove the parking brake cables, first remove the console and unclip the shifter bezel. Next, take out the armrest. Remove the two panels that are on the bottom back of the console. Behind those covers are four bolts that need to be removed. Slide the armrest up, revealing two screws on top of the console. Move the wires in this area out of the way of the parking brake.

Removing Classic Mustang parking brake cables

Step 21: Remove Mustang Drive Shaft

Make sure you have an extra set of hands for the next few steps. To remove the drive shaft, there are four 12mm 12-point bolts to unscrew. Before you do that, make sure your Mustang is in gear (manual) or park (automatic) and have a friend hold the axle still by locking a pry bar in the lug studs. After the bolts are removed, slide the drive shaft out of the transmission and set it aside.

Removing Classic Mustang drive shaft

Step 22: Brace Parking Brake Equalizer

Pull back on the parking brake equalizer so a second person can slip a rod through the handbrake to hold the spring in place.

Bracing a Classic Mustang parking brake equalizer cable

Step 23: Remove Parking Brake Equalizer Cables

Remove the cables from the equalizer and feed them through the turn wheel.

Removing Classic Mustang parking brake equalizer cables

Step 24: Remove Parking Brake Cable Retainer

Remove the parking brake cable retaining clip from the floorboards and unscrew the bolt on the cable that attaches it to the floorboard.

Removing Classic Mustang parking brake cable retainer

Step 25: Install New Parking Brake Cable

Install the new Mustang parking brake cable by feeding it back through the factory port until the clip clicks. Then, feed the cable through the turn wheel and back into the equalizer.

Installing a new Classic Mustang parking brake cable

Step 26: Hang Up New Cable

Feed the other end of the cable through the hole in the caliper and into the spring on the back of the caliper. Then, bolt up the new cable to the floorboard using the supplied retainer and factory bolts. You will probably need to use a pry bar to lift the cable.

Mounting new parking brake cables on a Classic Mustang

Step 27: Fill Differential with Gear Oil

Fill the differential with Mustang gear oil. Use a 3/8-inch socket to remove and tighten the differential retaining bolt.

Filling a Classic Mustang differential with gear oil

Step 28: Release Parking Brake Equalizer

Pull back on the parking brake equalizer, then pull the pin from the handle and slowly release the equalizer. Then, test the parking brake and reinstall the drive shaft along with the console and armrest.

Releasing Fox Body Mustang parking brake equalizer

Step 29: Bleed the Brakes

Keep the reservoir covered when bleeding the brakes, as air pressure can cause the brake fluid to shoot up and cover everything in brake fluid. Bleed each of your Mustang's brake lines, starting with the right rear and ending with the left front. From here, test your brakes at low speeds in a parking lot or another safe area to make sure everything is working properly.

Bleeding the brakes on a Classic Mustang

Upgrade the Rest of Your Classic Mustang's Brakes

Rear disc brakes are a great replacement for outdated brake parts. They give you a fresh brake system that will last for years to come. With your Fox Body Mustang converted to rear disc brakes, you will have more stopping power and improved vehicle safety.

If you're looking for more ways to upgrade your Fox Body Mustang's brakes, we offer a wide variety of options. From aftermarket calipers to rotors to brake pads, check out the button below to shop our selection of Fox Body Mustang brake parts.

This article was researched, written, edited, and reviewed following the steps outlined in our editorial process. Learn more about our editorial standards and guidelines.