Efficient braking performance is not only essential for vehicle safety, but for an enjoyable driving experience. No one wants a car that shudders, squeals, and vibrates to a stop. Yet, many enthusiasts’ vehicles do not stop properly. The braking system needs to be serviced and adjusted to produce expedient, smooth, and quiet deceleration. Often it is assumed that an older vehicle cannot stop on par with a modern one, but that is not true. Even the oldest car with hydraulic brakes can be made to instill confidence during normal driving scenarios. This can be accomplished by applying proper procedure to the entire braking system, no matter what brand of vehicle you own.
Speaking of procedure–when working on an engine you would never consider calling just a spark plug change a tune-up, right? Unfortunately, why does simply replacing the friction linings constitute a brake job to most mechanics? A proper brake job would address all three areas of the system. That is the hydraulic, friction, and mechanical components. They include:
Hydraulic: master cylinder, wheel cylinder, caliper piston (disc design), steel lines, and rubber hoses
Friction: shoes or pads, drums or rotors
Mechanical: springs, adjuster, anchors, slide pins, cables
Another fallacy is that four-wheel drum brakes need to be eliminated–and a disc brake conversion adapted–to an older vehicle. There is no denying that disc brakes offer improved stopping distances when measured in test protocols, but for a vehicle that is normally driven at legal speeds, drum brakes–when working efficiently–get the job done admirably. If road racing is your thing then a four-wheel disc brake conversion would be a must, but if you are just a cruiser, drums will be fine.
An aspect of brake performance that is not commonly recognized is the relationship of the compound of the friction material (shoes or pads) to the metallurgy and surface on the drums or rotors. All friction materials are not the same, and for this reason you should stick with name-brand parts. Likewise, a brake pad that is formulated for racing use will usually be a poor choice for street driving. Stopping distance, pedal feel, and general performance will suffer at lower pad temperatures, which are the result of not only the ambient conditions of the day but also how aggressive the stops are. A race pad on a 90-degree summer day will not stop as well as a standard design, let alone at 40 degrees.
Since proper brake service procedure is best shown by example, we worked with Bill Brownlee at Dimension Frame and Unibody who volunteered his 1972 Chevelle to represent the steps. The beautiful Chevelle was not in need of any brake service so none of the parts were changed. We took the system apart to photograph the procedure represented in the primer.
A common approach to brake service is to only institute service when the friction material is expired. The correct approach is to clean and lubricate the moving parts in between friction material replacement. This will ensure maximum brake performance and drastically improve friction material life. Most shoes and pads wear out prematurely due to poor mechanical conditions that cause constant contact and excessive wear. This is true on not only a hobby car, but on a daily driver as well.
A word about brake fluid: brake fluid is a desiccant, absorbing moisture very readily. Because of this brake fluid containers should be closed immediately after use, and old fluid left on the shelf of the garage should be discarded. When exposed to moisture, the boiling point of the brake fluid is greatly reduced and rust forms in the brake system. There are three different brake fluids: DOT 3,4, and 5. Most cars use DOT 3 from the factory. DOT 4 and 5 have a higher boiling point than 3 and are better for performance or road racing. Brake fluid types should not be mixed. If you want to upgrade, the entire system needs to be flushed.
It is important to note that even though our subject vehicle was a General Motors product, all of the procedures would be identical for any domestic car or truck. The only slight difference may be subtle design changes such as a Ford or Chrysler in some applications using a different caliper mounting. The same would hold true for some of the other car lines. So follow along as you learn to do the job right!
Are your brakes acting up? Use this chart to pinpoint the problem.
Extremely hard pedal: vacuum booster failing or failed
Spongy pedal: air in system, rubber hose weak and expanding under pressure
Excessive pedal travel: worn friction material or misadjusted shoes
Squealing: dust, incompatibility of friction material with contact surface, loose disc pads
Pulsation in pedal: Front rotor warped
Pulsation in chassis/body: rear drums or rotors warped
Pedal sinks: hydraulic leak
Pedal is at first hard and then slowly sinks: master cylinder seal leaking in the bore
TOOLS OF THE TRADE
A proper brake job can be accomplished with normal mechanics tools–with the exception of a brake spoon to adjust drum systems. Specialized brake service tools will make the task easier and faster, but in most instances are not required. The following is a list of dedicated brake tools that would be an asset to have. Cost will vary with quality and manufacturer, but in most instances everything listed can be purchased for $200.
Caliper piston retraction tool
Drum brake spring pliers
Drum brake retaining spring tool
One-man brake bleeder vacuum pump
Our subject 1972 Chevelle front brakes are single-piston-caliper discs. The caliper is what holds the brake pads and squeezes them against the rotor through hydraulic pressure. This action is created by the master cylinder when the brake pedal is depressed. Almost every domestic car has serviceable front-wheel bearings; some Corvettes use a non-serviceable hub bearing. Before disassembly, do a visual inspection of the rotor, caliper, and brake lines.
A common complaint with disc brakes is a rattle or noise created by a loose-fitting outside brake pad, or from missing anti-rattle clips. If you can move the pad with your finger then it will most likely make noise over bumps, or produce a clicking sound just as the brake pedal is applied. In some instances, the pad can be staked to tighten it up. Most calipers are a floating design. A single piston is used to create force on the inside of the rotor. The caliper moves on the pins as a result, allowing the outside pad to interact with the rotor. If the outside pad is worn more than the inside, that indicates that the sliders are frozen and not allowing the caliper to return after the piston is released. The slider pins hold the caliper to the mounting bracket. Always use the proper tool to remove the slide pins.
Once the caliper is detached, do not let it hang by the brake hose–instead, tie it to the frame so there is no tension. We used an old brake line bent into a hook. The sign of a poor mechanic is a caliper hanging by the brake line. Inspect the rubber brake lines for cracks and texture. Even though they may look good, over time the rubber becomes softened and allows the line to balloon out slightly as the brakes are applied. This decreases the amount of hydraulic pressure applied to the caliper, and impacts stopping ability greatly. The brake hoses should be changed every few years, especially if you live in an urban area with a high ozone content in the atmosphere.
If new caliper mounting bolts are not going to be used, clean and polish the old ones on a wire wheel. This will leave a smooth surface for the caliper to slide on. Before reassembly, lubricate the caliper slide boss with an approved high-temperature, water-resistant silicone brake grease.
The rotor or drum will need to be measured, and if there is enough thickness it can be turned on a lathe. All rotors and drums have cast into them a thickness dimension. The mass of the part is used to dissipate heat and to minimize warping. A thin rotor or drum will overheat and warp very easily.
Most auto parts stores offer a brake lathe service for drums and rotors. It is essential that the friction surface of the rotor is prepared properly for the brakes to work their best. When cutting drums or rotors, the goal is to remove the least amount of material to create a true surface. If the rotor is warped, it will cause a pulsing in the brake pedal when stopping. A second benefit of turning the rotor is the removal of the glaze that is created by the brake pad. Better brands of new drums and rotors leave extra material so they can be cut before they go into service to guarantee a true surface without sacrificing mass. If the parts were dropped during shipment, they will be warped.
Whenever performing disc or drum brake work, it is advisable to install new hardware. Though we’re working on the discs right now, here’s a drum-brake example: The paint on these springs is used not only as an anti-corrosion procedure, but also as an indicator of the spring’s service life. A shoe return spring with missing paint or a rusted surface indicates an overheated part that needs replacement to provide the proper tension.
Before the caliper can be installed with the new pads, the piston will need to be retracted. This can be done with a large Vise-Grip, a C-clamp, or a dedicated tool (shown). This process may require the removal of the lid from the master cylinder to allow it to accept the fluid from the caliper piston bore. (FYI: with the new pads installed, the master cylinder fluid level should come up to the proper range. This is a quick way to determine the wear of the brake pads: If the fluid is low and there are no leaks, the pads are worn.)
After cleaning, inspecting, and repacking the wheel bearings, the rotor can be installed. Follow the shop manual procedure for bearing pre-load. They are not all the same–a torque specification is usually provided. Remember, the wheel bearing and the race are made as a set. Always keep the wheel bearing with its race, even if the rotor comes with new races. Before assembly of the brakes always crack open the bleeder screws, and then retighten. If the screw breaks off or cannot be opened, now is the time to replace either the wheel cylinder or caliper.
Now on to the rear drum brakes. Most drums will have balance weights on them, so make sure that they did not fall off. To remove the drum, the emergency/parking brake will need to be released. If the drum is stuck it may require some force with a rubber mallet to be removed. It is common for the drum to rust around the axle shaft; you can use a rust buster such as WD-40 to help. Before reassembly, always coat the axle hub where it meets the drum with anti-seize compound.
With the drum removed, this is what you will see: There is a primary and secondary brake shoe. The smaller, shorter of the two is the primary, and always goes to the front of the car. It is designed to wrap into the drum, and help activate the secondary shoe through leverage. Some linings are bonded to the metal shoe, while others are riveted. This is a riveted lining. Before disassembly match up the new shoes to confirm they are correct. If you are a novice, as you take apart the brakes place the old parts in the appropriate place on the new shoe.
With the shoes removed, the parking brake cable will be hanging down. Inspect the cable for stretch, and pull on it to make sure it is not seized. If it is stuck it will need to be replaced.
Wash the backing plate with brake clean. Inspect the backing plate for any damage or cracks. The plate cannot be bent or warped.
Use Scotch-Brite to polish all shoe slide points, and the pivot of the center anchor. That is the round boss above the wheel cylinder.
Lubricate the slider points with silicone brake grease or anti-seize compound.
Check the wheel cylinder for leaks by gently prying back the boot. It should be bone dry. If in doubt, now is the time to replace or rebuild it.
Take the adjuster apart, wash, and then lubricate it with silicone brake grease. The oval hole in the backing plate is for access to the adjuster. There should be a rubber plug in the hole. If the plug is missing, water will enter the drum mechanism and create rust and brake fade in wet weather. The plugs are sold at most auto parts stores. Have the machine shop measure and then turn the drums to make them true. Reinstall the new brake shoes and hardware. Use emery cloth or sandpaper to remove any fingerprints and to scuff up the linings. Many old-time mechanics like to take a file and chamfer the leading edges of the brake shoes so they wear-in better and do not grab. This is optional. Install the drum and adjust the shoes so there is a slight drag on the drum when it is turned by hand.
Time to bleed the brakes. Even if the hydraulic part of the brake system was not opened, the lines should be bled. Before removing the lid from the master cylinder, wash it with brake clean. Any dirt entering the hydraulics will cause premature failure. On disc brakes, the fluid level is the adjustment. As the pads wear the fluid level will drop. If a bleeding tool (vacuum pump) is not available, two people will be required to manually bleed the brakes. Start with the wheel that is farthest from the master cylinder, which would be the right rear. Keep the lid on the master cylinder so that it does not spray fluid on the paint. When pumping the brakes, always keep your other foot or place a piece of wood under the pedal to limit the travel when the bleeder is opened. If you let the pedal go to the floor, the piston plunger cup seal will go past the bore and will usually result in failure of the master cylinder a short while afterwards. Let your helper pump the pedal until it is hard. With the pedal in the down position, open the bleeder screw until a stream of fluid exits. Repeat until there are no air bubbles. Close the bleeder screw when the brake pedal is down, or the system will suck air. Repeat for the other wheels while keeping mind of the fluid level in the master cylinder. You can now readjust the rear brake shoes if necessary. Install the tires and road test–your car should stop like never before.
Dimension Frame and Unibody
108 East Avenue
Hackettstown, NJ 07840