Replacing Disc Brake Pads

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This article covers the disc braking system, which is the most common brake system type on modern cars. In addition to describing the basic brake system operation, we will cover general procedures for replacing the one component of disc brakes that wear the fastest and require the most frequent replacement, the brake pads. Additionally, some tips are included for care, maintenance and prolonging brake pad life.

The brakes on a car are fundamentally simple. However, despite their simplicity, they are the single most important safety item on the car.

Improvements such as anti-lock braking have made the brake systems much more complicated over the years, but the basics remain the same. Brake designs and sizes vary as much as the cars they are used on, but in general you can count on:

• Your foot stepping on a pedal...
• to generate hydraulic pressure...
• which causes the brake piston to move…
• and press friction material against a piece that is solidly bolted to the car’s wheel.

The result is that a lot of friction and heat is generated between the brake disc (the piece that is solidly bolted to the car’s wheel) and the brake pads (the friction material) with the car slowing nicely in direct correlation to how much hydraulic pressure you generate when you step on the brake pedal.

See, it is simple. In modern cars there may be a bewildering mess of sensors and attached wires that enter “black boxes” to monitor and aid brake system operation, but the main components operate much the way they have since brakes were first invented. Because of this, the average home mechanic can safely replace the parts that wear normally.

IMPORTANT: This article is intended as a guide only, and should not be considered as a replacement for a complete repair manual. It does not address all the potential variations between different vehicles and manufacturers. Be sure and figure this into your plans. As previously stated, your brakes are the most important safety item on your car. If at any point you feel as if you have gone beyond your comfort level, seek professional advice.

Tools and Materials

Make sure you have the necessary tools and materials “on hand” before you begin. In addition to the new brake pads, you will need a few basic mechanic’s tools:

• Floor jack (a hydraulic jack is best but the car’s emergency jack can be used in a pinch)
• Wheel chocks (at least two, one for in front of a wheel and one for behind)
• Wrenches in the appropriate sizes
• C-clamp or large channel pliers
• Torque wrench and appropriately sized socket (for the caliper retaining bolts)
• Pry bar or large screwdriver

You may also want to be prepared with a couple additional materials that will minimize the need to revisit this job sooner than necessary:

• Caliper lube
• Anti-squeal compound/spray

Procedure

Make sure you are familiar with the parts you’ll be working with before you begin. The basic components of a typical disc brake system are shown below.

When jacking up a car, ALWAYS chock the wheels and put it into gear/park. ALWAYS use jack stands. NEVER use only a jack to hold the vehicle up. Be certain that the car is well supported on the jack stands.

Fuel Tank

The fuel tank is nothing more than a reservoir for the vehicle’s fuel. However, in older vehicles, or vehicles that are driven infrequently, it is the primary source of fuel system contamination. Metal tanks -- common on older cars -- can be a big problem. Metal tanks rust because of condensation in the airspace of the tank. When a vehicle is driven regularly, the sloshing fuel keeps the tank sides clean. When the sits “idle” for long periods of time, water condensation has a chance to eat away at the metal. Then, when the vehicle is driven again, the sloshing fuel pulls the rust scale off the sides of the tank and send bits of this debris into your fuel system, where it clogs filters and pumps.

Get the vehicle in place and ready for servicing.

• Begin by loosening the lug bolts/nuts slightly while the vehicle is still on the ground. This makes it easier to remove them once the wheels are in the air.
• Chock the wheels that will remain on the ground, and place the transmission in “gear” or in “park” (depending on whether you have a manual or automatic transmission).
• Using the approved jacking points (see the Owner’s Manual for your vehicle for locations), jack the vehicle up to a comfortable height, and position it securely on jack stands. Take great care doing this to prevent potential injury or damage to the vehicle.
• Remove the wheels and place them under the car until you need them again.

Inspection

Take a moment to inspect the brake components. Parts that show abnormal or excessive wear or other damage should be replaced.

• Inspect the brake disc for abnormal or excessive wear.
  ● Look for deep grooves, discoloration or scores in the surface. Slight variations in the surface are normal and nothing to be concerned about. If excessive scoring or discoloration is present, replace the rotor.
  ● Look for cracks in the disc surface. Any crack is reason to replace the disc.
  ● Measure the disc thickness with a micrometer or caliper. The minimum allowable thickness is normally stamped somewhere on the disc. If not, look for the specification in the vehicle’s repair manual. If the disc is thinner than the minimum allowable thickness, replace the disc.
  
• Inspect the brake hoses for cracks or signs of leaking.
• If present, inspect the anti-lock brake sensor wires and pad-wear sensor wires for cracks or breaks.

Prepare the Brake Pads

Following the directions on the product, apply anti-squeal compound/spray to the BACK of the brake pads.

NOTE: Some products are applied to the friction material surface, but these are less common.

Replacement

These steps will vary depending on the design of your particular brake caliper.

Work on one side of the vehicle at a time so that you will always have a ready reference to the correct assembly.

• Remove the caliper retaining bolts. These are located on the inboard side of the caliper, and fasten the caliper to the rest of the suspension.
• Carefully remove the caliper by sliding it off the brake disc. (This is where a pry bar might come in handy.)
  
  NOTE:
  DO NOT let the caliper hang from the brake hose. It puts too much stress on the hose and fittings. Instead, form a piece of heavy wire (like a wire coat hanger) to act as a hook and use it to suspend the caliper while you work with it.
  
  DO NOT step on the brake pedal when the caliper is removed. The piston will pop out of the caliper. It will be messy and difficult to get back in, and may require a new seal.
• Remove the old brake pads from the caliper (or pad carrier if your brakes use this design). This may require the removal of retaining clips or bolts. If there is a pad-wear sensor, disconnect it at this time.
• Using a C-clamp or channel pliers, press the caliper piston back into the caliper body to make room for the new (thicker) brake pads. Take care not to mar the piston surface DO NOT to press the piston in farther than necessary to install the new pads.
• At this point, clean the sliding surfaces and/or guide pins and apply caliper lube to these points. This will ensure proper operation and prevent premature wear.
• Install the new (prepared) brake pads in the caliper (or pad carrier) in the same position as the ones you removed. If anti-squeal shims were present originally or were provided with the new pads, install them according to the manufacturer’s instructions.
• Reinstall the pad retaining clips or bolts (and pad wear sensor if present).
• Reinstall the caliper over the brake disc and install the caliper retaining bolts.
• Use a torque wrench to tighten the caliper retaining bolts to the manufacturer’s prescribed torque (generally 80 to 90 ft-lb).
• Check the other side of the car and compare your reassembled side to the not-yet-disassembled side to verify proper assembly.
• Check the brake fluid level. Since you pressed the piston back into the caliper it is possible that the fluid level has risen and is at risk of overflowing. Remove any excess if necessary. An old turkey baster works well for this purpose.
• Move to the other side of the vehicle and repeat the process.
• When complete, step on the brake pedal and ensure that it feels solid.
• Re-check the brake fluid level and add or remove fluid as necessary.
• Refit the wheels, tightening the lugs to the prescribed torque.
• Carefully lower the car off the jack stands.

Test Drive and Break-In

It is necessary to go for a test drive and ensure that the brakes work properly. Before you go for a drive, press gently on the brake pedal several times to seat the pads. Take great care the first time you step on the brakes! The first time you use them they may be ineffective for a moment. Don’t find out about this in the middle of an intersection with a dump truck loaded full of compost bearing down on you!

Check the documentation that came with the new brake pads. If there is a prescribed break-in procedure, follow those instructions closely. Otherwise, simply avoid excessively hard or long applications of the brakes for the first 100 to 200 miles of driving.

During the first couple of hundred miles on a new set of brake pads, allow for slightly longer braking distances. The brakes may feel slightly spongy and less effective than usual. This is to be expected and will go away as the brakes “break in.”

Care and Maintenance

The following practices and procedures will help prolong the life of your brakes, as well as helping to ensure that they’ll be ready when you need them!

Brake EARLY, Brake LIGHTLY

Depending on the conditions you drive in, your brakes can last a very long time. Generally, city driving is harder on brakes than highway driving. You can prolong the life of your brakes by applying your brakes earlier and lighter for longer distances rather than waiting and applying them later, harder and for shorter distances.

DO Use Them On Hills

Most people will tell you to save your brakes going down long hills by shifting to a lower gear rather than riding the brakes to maintain your speed. This is almost entirely wrong, and originates from a time years ago when brakes were not as capable as they are today.

Shifting to a lower gear will indeed help keep the speed of the car under control going down long hills, but it also places stress on the transmission in the opposite direction for which it was designed. Brake pads and discs are cheap, transmissions are expensive. Brakes wear out gradually over time and provide plenty of visual and audible signs to alert you when they will need replacing. Transmissions often break suddenly and consistently at the most inconvenient time or place.

There was a time when the “lower gear downhill rule” made sense and for certain vehicles, and in some cases it still does. Back when drum brakes were more common and less capable of keeping themselves cool, it was possible that extended periods of braking could overheat the brakes and cause them to fail. This was most common on heavy vehicles like trucks, and can still be an issue for the big 18-wheeler type of truck. With the advent of disc brakes and vented discs, the problem has been virtually eliminated in modern passenger cars and trucks.

Check Them REGULARLY

About every 10,000 miles, take a visual inspection of your brakes. With the open design of some wheels, you can often see at least one brake pad without even removing the wheel. Now that you have “been there” and “done that”, you know pretty well what you are looking for. Don’t allow the friction material of the pad to get below about 3/16 of an inch (4 to 5 mm) in thickness.

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