Brake Shim Installation Guide

Brake shims are a small but mighty component in your vehicle's braking system, often overlooked but crucial for a quiet and efficient stop. These thin, often metal or composite layers are fitted between the brake pad and the caliper piston. Their primary function is to dampen vibrations that can travel through the braking system, preventing that irritating squeal or groan that can plague even the best-maintained vehicles. While the process of replacing brake pads often involves installing new shims, understanding how to install them correctly, whether as part of a pad replacement or as a standalone fix for noise, is a valuable skill for any DIY mechanic. This guide will walk you through the process, ensuring you can tackle this job with confidence and achieve a quieter, smoother braking experience.

Why Install Brake Shims?

The rhythmic squeal of brakes is more than just annoying; it's a symptom of microscopic vibrations occurring between the brake pad and the rotor, and more specifically, between the brake pad and the caliper piston. Brake shims act as a vibration damper. When the brake pad is pressed against the rotor, it also presses against the caliper piston. Without a shim, this metal-on-metal contact can cause rapid, high-frequency oscillations. Shims, with their layered construction and often a damping material in the middle, absorb these oscillations, preventing them from being transmitted as audible noise. Beyond noise reduction, some shims can also help to dissipate heat, although this is a secondary benefit. Ultimately, installing or replacing brake shims is an effective way to address brake noise and ensure a more comfortable driving experience.

When Should You Install Brake Shims?

The most common time to install new brake shims is when you are replacing your brake pads. Many aftermarket brake pads come with shims already attached or included in the packaging. If your old pads had shims, it's almost always recommended to fit new ones with your new pads. Other scenarios where installing shims is beneficial include:

• Addressing persistent brake squeal: If your brakes are making noise and you've ruled out other issues like worn rotors or sticking caliper pins, new shims can be an effective solution.
• Preventative maintenance: If you're performing a comprehensive brake service, fitting new shims is a good practice to ensure long-term quiet operation.
• After caliper servicing: If you've had your calipers serviced or replaced, it's a good opportunity to install fresh shims.

Tools and Materials You'll Need

Before you begin, ensure you have the necessary tools and materials to complete the job safely and efficiently. These typically include:

• New Brake Pads: Ensure they are the correct type for your vehicle.
• New Brake Shims: If not included with your pads, purchase the correct ones for your vehicle and pad type.
• Jack and Jack Stands: For safely lifting and supporting the vehicle.
• Lug Wrench: To remove the wheel nuts.
• Socket Set and Ratchet: For removing caliper bolts.
• C-Clamp or Piston Compressor Tool: To retract the caliper piston.
• Wire Brush: For cleaning caliper brackets and pad contact points.
• Brake Cleaner: To ensure all surfaces are clean.
• High-Temperature Brake Grease: Specifically designed for brake components.
• Gloves and Safety Glasses: For personal protection.
• Torque Wrench: For tightening bolts to the manufacturer's specifications.

Step-by-Step Installation Process

Installing brake shims is best done as part of a complete brake pad replacement. Follow these steps carefully:

Step 1: Safely Lift and Support the Vehicle

Park your vehicle on a level surface and engage the parking brake. Loosen the lug nuts on the wheel you'll be working on, but do not remove them yet. Use your jack to lift the vehicle and place a jack stand securely under a strong point of the chassis. Gently lower the vehicle onto the jack stand. Remove the lug nuts and take off the wheel.

Step 2: Remove the Caliper

Locate the brake caliper. It's the assembly that straddles the brake rotor. You'll typically need to remove two bolts that hold the caliper to the caliper bracket. These are often referred to as guide pin bolts or slider bolts. Once the bolts are removed, you should be able to pivot the caliper upwards and away from the rotor, or in some cases, you may need to slide it off completely. Be careful not to let the caliper hang by the brake hose; use a piece of wire or a bungee cord to support its weight.

Step 3: Remove the Old Brake Pads

With the caliper out of the way, you should be able to easily slide the old brake pads out of the caliper bracket. Note how they are oriented, as the new ones will need to be installed in the same way. If the old pads have shims attached, carefully remove them. Some shims are clipped on, while others might be bonded.

Step 4: Clean the Caliper Bracket and Pad Contact Points

This is a crucial step for ensuring proper operation and preventing future noise. Use a wire brush to thoroughly clean the areas on the caliper bracket where the brake pads sit and slide. Remove any rust, dirt, or old grease. Spray brake cleaner onto a clean cloth and wipe down these surfaces, as well as the back of the caliper where the piston presses against the pad. A clean surface is essential for the grease to adhere properly and for the new pads to seat correctly.

Step 5: Prepare the New Brake Pads

Take your new brake pads. If they came with separate shims, carefully attach the shims to the back of each brake pad. The shims are designed to fit specific pads, so they should slot or clip into place. Ensure they are securely fitted and oriented correctly. Some modern brake pads have integrated shims, meaning they are already part of the pad assembly and require no separate installation.

Step 6: Apply Brake Grease

Apply a thin, even layer of high-temperature brake grease to the back of the new brake pads where they will contact the caliper piston and the caliper bracket ears. Do not get grease on the friction material of the pad or the rotor surface, as this will severely compromise braking performance. The grease helps to further dampen vibrations and prevent seizing.

Step 7: Reinstall the Brake Pads

Slide the new brake pads into the caliper bracket. Ensure they are seated properly and can move freely. If they are a tight fit, double-check that you've cleaned the bracket thoroughly and that no debris is obstructing their movement. Make sure the shims are correctly positioned and not interfering with the pad's seating.

Step 8: Retract the Caliper Piston

Before you can put the caliper back over the new, thicker brake pads, you'll need to retract the caliper piston(s). Use a C-clamp or a dedicated piston compressor tool. Place the old brake pad against the piston and slowly compress the piston back into the caliper housing. You may need to open the bleeder valve slightly to allow brake fluid to escape into a catch pan, especially if your brake fluid level is near the maximum. This prevents overflow. Once the piston is fully retracted, close the bleeder valve if you opened it.

Step 9: Reinstall the Caliper

Carefully lower the caliper back over the new brake pads and rotor. Reinsert and tighten the caliper bolts to the manufacturer's specified torque. Do not overtighten, as this can strip the threads or damage the caliper. Ensure the caliper slides smoothly on its pins if it's a floating caliper design.

Step 10: Reinstall the Wheel and Lower the Vehicle

Replace the wheel and hand-tighten the lug nuts. Carefully lower the vehicle off the jack stand. Once the vehicle is on the ground, tighten the lug nuts firmly in a star pattern. Repeat the entire process for the other side of the same axle.

Step 11: "Bed In" the Brakes

After installing new pads and shims, it's essential to "bed in" the brakes. This process transfers a thin layer of pad material to the rotor surface, ensuring optimal performance and quiet operation. Perform several moderate stops from around 30-40 mph down to 10 mph, without coming to a complete halt. Avoid hard braking for the first few hundred miles. Consult your new brake pad manufacturer's recommendations for specific bedding-in procedures.

Common Brake Shim Types

Brake shims come in various forms, each designed to offer specific damping characteristics:

Troubleshooting Common Issues

Even with careful installation, you might encounter issues. Here are some common problems and solutions:

Brake Squeal Persists

• Check shim placement: Ensure shims are correctly seated against the piston and not loose.
• Improper grease application: Too little or too much grease, or grease on the friction surface, can cause issues. Reapply correctly.
• Uneven pad wear: Check for warped rotors or sticking caliper pins.
• Incorrect shim type: Ensure you are using the correct shims for your pads and vehicle.

Brake Pads Binding

• Over-greasing: Excessive grease can sometimes get into the pad backing and cause it to stick.
• Debris: Ensure all cleaning was thorough and no grit is present.
• Shim interference: A bent or improperly fitted shim could obstruct movement.

Frequently Asked Questions (FAQs)

Q1: Do I need to replace my brake shims every time I replace brake pads?

A: It is highly recommended. Shims are designed to dampen vibrations, and over time, the damping material can degrade or compress. Using old shims may not provide the same level of noise reduction and could lead to premature brake noise.

Q2: Can I drive without brake shims?

A: Yes, you can drive without shims, but your brakes are more likely to be noisy. Shims are not a critical safety component in terms of stopping power, but they are essential for noise reduction and a comfortable ride.

Q3: How do I know if my shims are installed correctly?

A: They should fit snugly against the back of the brake pad, without being loose or interfering with the caliper's ability to seat properly. The shim should also be in contact with the caliper piston.

Q4: What is the difference between shims that clip on and ones that are bonded?

A: Clip-on shims have small tabs that grip the edges of the brake pad, making them easier to remove and replace. Bonded shims have the damping material permanently adhered to the steel backing, offering a more robust connection but can be trickier to remove if damaged.

Q5: Can I reuse old brake shims?

A: While technically possible, it is strongly advised against. The effectiveness of the shim's damping properties diminishes with use. Reusing old shims is a false economy and may lead to brake noise returning quickly.

By following these steps and understanding the role of brake shims, you can effectively maintain your vehicle's braking system for a quieter, more pleasant driving experience. Remember to always prioritise safety and consult your vehicle's service manual for specific torque specifications and procedures.