Front Disc Brake Conversion – Part 2

In Front Disc Brake Conversion Part 1, I went through the components needed to convert a front drum brake vehicle to front disc brakes. This month we’ll install that disc brake conversion kit.

First Step

Start by removing the drum brake assemblies from the car. Once you remove the drums, you’ll find brake shoes, springs, and a backing plate. If you have problems getting the drums off, here is what you do next. Notice that on the back side of the backing plate, near the bottom of the plate, you will find a slotted hole. Generally this hole is capped with a black rubber plug to help keep dirt from the brake shoes. Remove the plug, and with a shop light look into the hole. When you see the geared brake adjustment wheel. Use a flat bladed screwdriver to reach through the opening and turn the gear counter-clockwise. That will release the tension on the brake shoes and allow the drum to come off.

Note: On some vehicles you may also need to remove the spindle nut to release the drum.

Also by the way, wear a dust mask as you work. In the old days brake shoes were made of asbestos. Now, brake shoes are made of alternative compounds, but just the same, they create dust.

Now that’s the drums are off you can remove the brake shoes. All brake shoes are attached to the backing plates with springs. Remove all of the springs and the shoes will come off.

With the brake shoes removed the backing plates will come off next. These backing plates will have two to four bolts, depending upon the vehicle, attaching them to the spindles. Then, you will also need to remove the flexible brake lines from the connections on the frame rail tabs. The result of all this removal should leave you with a dirty spindle. Take a wire brush and clean it up.

The spindle is attached to the upper and lower control arms at the ball joints. This might be a good time to grease those ball joints. But whatever you do, don’t remove the nuts holding the ball joints to the spindle. Doing so can release the stored energy in the coil spring and result in crushed fingers, gouged eyes, broken bones, and the need for a long explanation at the hospital while they sew you up.

At this time we’re ready to mount the disc brake caliper mounting bracket to the spindles. First, you will need to press the two steel thread inserts into the aluminum caliper mounting bracket. We‘ll use the left side as our working example and start with the aluminum caliper mounting bracket and attach it to the spindle using new grade 8 bolts in the same positions as the original backing plate used. . These bolts are torqued to the same specs as the original units. A drop of Lock-Tite® on the threads is not a bad idea at this time.

Rotors and Calipers

The kit will come with a pair of cast iron vented rotors and a pair of machined billet aluminum hub. To mount these rotors it is a straight forward matter of installing the new bearings and rear seals into the hubs then bolting the rotors to the hubs, using grade 8 safety-wire bolts. This is a great time to use safety wire and/or Lock-Tite® again.

Have you ever packed a wheel bearing? Here’s the trick. Scoop out a tablespoon sized glob of axle grease into the palm of your hand. Hold the bearing upright with the other hand and force the bearing into the grease taking care that the grease is pushed between each of the bearing rollers. Make sure that grease migrate all the way to the top of the rollers. The entire glob of grease should disappear into the bearing as you work. It may take more than one glob of grease to get the bearing filled. The bearing is now properly serviced.

Now, install the rotor with the new bearings, snug tighten the castle nut, add the castle nut lock cap, insert a new cotter pin, and then cover the castle nut with a supplied dust cap.

The disc brake calipers that come in the kit will be ‘loaded’. This means the calipers come with the brake pads already installed.


Secondly, slide the calipers into place over the rotors, and attach the two bolts.

Before snugging down the caliper mounting bolts, check to make sure that the caliper brake pad are centered. The clearance should be the same for both pads and the rotor. If they are not, try installing spacers between the caliper and the mounting bracket. Keep making adjustments until the clearance is equal.

Brake Lines

The first lines to be attached are the flexible lines going from the frame out to the calipers. These lines take the place of the old rubber coated flex lines with one end being attached to the brake line tab on the frame and the other being attached to the caliper. To attach these lines to the frame, use the adapter (AN-3 to 3/16 inch line) attach to the new flexible line. The other end will attach to the caliper using another adapter (AN-3 to 1/8” NPT).

Make certain the new flex lines are long enough. With the lines bolted to the disc brake calipers and attached to the brake line tabs turn the steering wheel from full lock right then left. The flex lines must be long enough that they are not stretched at any point. Do this with the front end off the ground. If they are not long enough? Don’t panic. This is a common problem. Remove one of the flex lines and connect Summit Racing or Jegs and request a longer line, probably for a 1980 Camaro. This car uses longer flex lines.

Master Cylinder Installation

Installation of the new unit is pretty simple. Just remove the old master cylinder and replace it with the new master cylinder and power brake booster combination.

There is a little more than that. Before you remove the old master cylinder remove the pin securing the master cylinder piston rod to the brake pedal. Many times these rods are secured to the master cylinder with plastic retainers and they can be very difficult to remove. This can happen even with the master cylinder on the bench. Removing this pin at the pedal makes removal of the unit from the car much easier.

To get one of these pins out of the master cylinder? Vise Grip pliers and a little leverage will pop the pin right out.

Did your new master cylinder and power brake booster unit come with a new rod already attached and is it the correct length? You must measure both of them and adjust the new one if necessary.

Before you mount the new master cylinder and power brake unit look for the bleeding instructions that come with the master cylinder. Most manufacturers recommend some sort of bench bleeding. We will discuss that in a moment. After the master cylinder has been bled and you are ready for installation don’t forget to hook up the brake pedal before advancing on to the brake lines.

Steel Brake Lines

These fitting may not come in your kit. Don’t worry, Summit Racing, Jegs or your local parts store will have an assortment of brake line fittings. Just be sure the fittings your purchase is for brake line use.

What you will need are all 3/16 brake line fittings. One ‘T’ coupling, one 90 degree coupling, and two union couplings are what are required.

The ‘T’ coupling is used to join both right and left front brakes together as well as join to the master cylinder. The union couplings and the 90° coupling will help facilitate the installation into the rear brake line as well as help with the change of routing of the rear brake line. When bending the brake lines, you must use a tubing bender to prevent kinking the tubing. Units for this operation can be purchased at your local parts store, on line, or from Eastwood (#49045). A good idea is to purchase an extra length of brake line tubing and practice making bends.

Production vehicles have the two lines coming from the master cylinder with coils in them. You don’t have to make these coils, but you should bend the lines going to the master cylinder into either ‘S’ shapes or coils. This is a safety precaution that stems directly from crash testing done by the manufactures in Detroit . In a severe crash things tend to move around a bit. Having coils or ‘S’ shapes between the brake lines secured to the frame rails and the master cylinder secured to the body provides slack for that movement and prevents the brake lines from coming under stress and fracturing.

Note: Some kits will have these lines already coiled.

Bleeding the System

This starts with the master cylinder. The instructions that come with the new master cylinder will illustrate the procedure for bleeding the unit on the bench using two curved lines that attach to the master cylinder outlet connections and turn up and into the bowls. With the unit clamped firmly in a vise fill the bowls with clean fluid then push the piston several times until no air bubbles can be observed coming from the submerged tubes.

Then remove the curved tubes, cap the bowl inlets and install the unit on the car. You can make the curved tubes by purchasing a couple of short lengths of brake line from your local parts store and bend them to specs. By the way, be sure the end fittings will screw into the master cylinder before you buy them and bend them.

Now, with the master cylinder mounted on the vehicle and all lines connected start the bleeding process as the driver’s front wheel. Attach a brake vacuum bleeding pump to the bleeder screw located on the back of the caliper and operate the pump until the fluid runs clear, no air bubbles. Next, repeat at the passenger’s front wheel then test the brakes. The pedal should be firm and should not have to be pumped to achieve good brakes. If you have to pump the pedal repeat the bleeding procedure until the pedal becomes firm and don’t forget to maintain sufficient fluid in the master cylinder throughout the process.

Adjusting the Proportioning Valve

Front to rear brake balance should be set so that the front brakes lock up just ahead of the rears locking up. This seems like a two person job, one to drive, one to watch the rear wheels. Try making all adjustments at the proportioning valve at low speeds, a half turn at a time, and only when you are certain the setting is just right, the front brakes locking up followed by the rear brakes. Carefully increase the vehicles speed and recheck.

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Marcus Simmons, ASE Certified
Phone: (248) 461-6977