Brake Pad Shims Selection: Things to Consider
Brake pad shims play a critical yet often overlooked role in the braking system of vehicles. This article will provide a comprehensive overview of brake pad shims – explaining what they are, why they are important, the different types available, key design considerations, and best practices for installation and maintenance.
Brake pad shims are thin pieces of metal or fiberboard that sit between the brake pad and caliper piston. While small, these shims serve the vital functions of damping vibration, reducing brake noise, and protecting the caliper piston from direct contact with the brake pad material. Without proper shims, braking performance and component longevity can be compromised.
We will explore the various shim designs, materials, sizing, and compatibility factors that must be considered for optimal braking function. Proper shim selection, installation, inspection and replacement procedures will also be covered. After reading, you will have a full understanding of this small but critical brake system component.
What Are Brake Pad Shims?
Brake pad shims are thin metal or rubber spacers that are installed between the brake pads and caliper pistons in disc brake systems. They serve several important functions:
Brake pad shims help center the brake pads on the caliper bracket properly and reduce vibration and noise. The even spacing provided by shims allows for smooth pad movement and prevents the pads from rocking or shifting during braking. Shims dampen vibrations between the pads, pistons and caliper bracket (https://oards.com/brake-pad-shims/).
Shims also help distribute the hydraulic pressure from the brake caliper pistons evenly across the pad surface area. This prevents uneven pad wear and allows the maximum braking force to be transferred to the rotor. The shims compress slightly under pressure to evenly spread the load.
Most brake pad shims are made from thin stamped steel but some are made of firm rubber or other materials. Steel shims can be coated or plated to resist corrosion. Rubber shims provide vibration damping but are less durable than metal shims.
Why Are Brake Pad Shims Used?
Brake pad shims are primarily used to prevent brake noise and vibration issues. When the brake pads press against the brake rotor during braking, small vibrations can occur between the pads and caliper bracket. Over time, these vibrations lead to irritating brake squeal or squeaking noises.
Brake pad shims create a barrier between the brake pads and caliper, absorbing and dampening the vibrations that lead to brake noise. The shims help prevent metal-to-metal contact between the pads and caliper, reducing the occurrence of squeaks, squeals and other NVH (noise, vibration and harshness) issues.
By installing the correct shims between the brake pads and caliper, the transmission of vibration during braking can be significantly reduced. Brake pad shims have a damping effect that diminishes and absorbs the vibrations before they have a chance to turn into audible brake noise (Advics).
Types of Brake Pad Shims
Two main types of brake pad shims are used on vehicles:
Insulator shims
Insulator shims, sometimes called anti-rattle shims, are thin pieces of material placed between the brake pad and brake caliper piston. They help minimize vibrations and noises that can occur when the brake pads are applied. Insulator shims are typically made of rubber, plastic, or metal. They provide a damping and insulating effect to smooth out brake operation.
According to Advance Auto Parts, popular insulator shim brands include Volvo, Raybestos, Wagner, and Bendix.
Dampener shims
Dampener shims are thicker, soft shims installed between the brake pad back plate and brake caliper. Their main purpose is to dampen vibrations caused by slight differences in the brake pad and rotor surfaces. The soft dampener shim material absorbs these vibrations to prevent brake noise and improve pad contact with the rotor.
Well-known dampener shim manufacturers include Porsche, Akebono, and Brembo, according to Advance Auto Parts. These are usually original equipment shims matched to specific vehicle models and brake pad sets.
Key Design Considerations
Several key factors should be considered when selecting brake pad shims, including:
Thickness – Thicker shims can help reduce vibration between the brake pad and rotor, but too thick may cause issues with brake pad seating and proper caliper movement. Most shims range from 0.002-0.008 inches thick. According to one source, “Shims that are too thin may not dampen vibrations properly. Shims that are overly thick can prevent pads from seating properly” (Source).
Coverage Area – The shim should cover as much of the brake pad surface as possible, without going over the edge. Complete coverage helps reduce noise and vibration. Partial-coverage shims may still provide benefits but can allow spots for noise generation.
Stickiness – The adhesive backing should securely hold the shim in place during braking. Low stickiness can allow the shim to shift or detach. Using shims with a strong pressure-sensitive adhesive prevents movement.
Materials – Most shims are made from rubberized materials that dampen vibration. Stiff metallic shims are discouraged as they transfer noise. According to experts, softer shims made from materials like felt, rubber, or foil are preferred (Source).
How to Install Brake Pad Shims
Installing brake pad shims is a straightforward process, though proper preparation is key. Here are the basic steps for installing shims:
First, thoroughly clean the brake pad surface where the shim will be applied using brake cleaner or rubbing alcohol to remove any dirt, grease or debris. Allow the pad to dry completely.
Peel off the adhesive backing from the brake pad shim. Avoid touching the adhesive surface so it retains maximum stickiness.
Orient and align the shim properly on the brake pad. Press the shim firmly into place, starting from one side and smoothing across to fully adhere it. Apply heavy pressure with your fingers across the entire shim to ensure full contact with the brake pad.
If the shim does not fully stick at first, gently lift it up and re-clean the brake pad surface before re-applying. The adhesive should create a strong, lasting bond if the pad is cleaned properly.
Refer to your vehicle repair manual for the recommended shim location on your brake pads. Some shims install on the leading and trailing edge of the pad.
Allow several hours for the adhesive to fully cure before re-installing the brake pads and rotor. Test braking performance carefully after completing the job.
Sources:
https://mycarmakesnoise.com/brakes/what-do-brake-pad-shims-do-in-a-car/
Diagnosing Issues with Brake Pad Shims
There are some telltale signs that issues may exist with the brake pad shims in your vehicle. The most common symptom is brake squeal, especially when coming to a stop. This high-pitched squeaking or squealing noise indicates that the brake pads are vibrating inside the caliper bracket. Without properly aligned and fitted shims, the pads can shift and move, causing the noise.
To inspect for issues, you’ll need to remove the wheels and visually examine the brake pad shims. Look for any deformation, tearing, cracking, or other damage to the shims. Also check that the shims are still properly aligned and haven’t become tilted or slipped out of position. While the pads are removed, examine the caliper bracket for any galling or damage that could be impacting shim fitment.
This Reddit thread discusses a case where the shim had slid partially off the brake pad, causing noise.
Replacing any damaged, misaligned, or missing shims will be required to resolve issues and stop brake squeal.
Replacing Worn or Damaged Shims
Over time, brake pad shims can become worn down or damaged. Here are some signs that indicate it may be time to replace your shims:
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You hear a scraping or squealing noise when applying the brakes. This can indicate that the shims have worn too thin and are no longer damping vibration properly.
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Upon visual inspection, the shims appear cracked, bent, or otherwise damaged. Severely warped or broken shims will not function correctly.
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There is a pulsation felt in the brake pedal. If the shims are not providing even support to the brake pads, it can cause pedal pulsation.
Replacing worn or damaged shims is usually straightforward:
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Remove the brake caliper and brake pads from the caliper mount following the procedure in your vehicle service manual.
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Carefully remove the old shims from the brake caliper or brake pad backplates.
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Clean the caliper and brake pad contact areas to ensure good adhesion of the new shims.
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Apply the new shims in the same locations as the old ones, following any instructions provided with the replacement shims.
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Reinstall the brake pads and caliper.
Be sure to get quality replacement shims designed specifically for your vehicle. Follow all reassembly procedures to ensure the brakes are working safely.
Best Practices
When installing brake pad shims, it’s important to follow the manufacturer’s instructions closely. The automotive parts supplier may include specific guidelines on proper shim selection, preparation, and installation that should be followed for optimal performance and safety.
Brake pad shims are precision-fit parts and need to be handled carefully to avoid damage. They should be stored in sealed packaging away from moisture, dirt, and grease. Before installation, shims should be visually inspected for deformities, tears, or contamination. Any compromised shims should be replaced.
Most shims are designed for one-time use only. Reusing old shims that have been subjected to heat cycles can diminish their effectiveness over time. For best results, always replace shims whenever brake pads are swapped out.
Properly lubricating contact points between the shim, brake pad, and caliper can reduce noise. Use only approved brake lubricants and apply sparingly as directed. Too much grease can damage shims or degrade braking capability.
Following the recommended procedures from component manufacturers and exercising prudence in handling brake parts helps ensure proper shim function and braking system longevity.
Conclusion
In summary, brake pad shims play a crucial role in proper brake system functioning. They help reduce vibration, minimize brake noise, and promote even pad wear. Selecting the correct shim thickness and type is important to achieve optimal performance. Key considerations include the brake pad and caliper design, vehicle model, driving conditions, and required noise dampening levels.
Taking the time to properly install new shims per manufacturer specifications helps ensure maximum effectiveness and brake pad life. Periodically inspecting shims during brake service allows for replacing damaged or worn-out shims before they cause issues. Proper shim selection, installation, and maintenance leads to a smoother, quieter brake system with enhanced safety and responsiveness.