Most people understand the main components of a vehicle’s braking system. You have the master cylinder, lines, rotors (or drums), brake pads (or shoes), brake booster, and pedal.
But one small component plays a major role when it comes to brake noise. Here’s everything you want to know about brake pad shims which are sometimes referred to as anti-squeal shims.
What are Brake Shims?
Simply put, the main function of brake pad shims is to prevent brake noise. At each corner of a vehicle, brake pads and brake rotors (or drums) sit very close to each other. The only thing that stops them from clanging together is the brake shim.
The brake pad shim is a component which goes in between the calipers and pads to prevent friction from occurring. Basically, the shims keep them aligned with each other, so they can function without generating noise.
These anti-squeal shims are either adhesive or non-adhesive pads made of either rubber or metal. They go in between the middle of the brake calipers and brake pads.
If a brake shim were to become damaged or removed, then too many imperfections would exist between the rotors and pads. This would cause them to clang together and make strange noises. You will hear these noises each time you step on the brake pedal.
Can You Install Brake Pads Without Shims?
Yes, you can install brake pads without shims, although shims are generally recommended. Shims serve to reduce noise and vibration, but they do not affect the performance of the brake pads themselves.
For example, a discussion on Honda-Tech mentions that shims are just there to reduce noise and vibration and do not affect performance. However, it’s important to note that while you can run without shims, they do help in preventing squealing and allow for quieter operation.
Is Brake Pad Grease Necessary?
If you have brake shims installed between your brake calipers and brake pads, there may still be instances when you hear noises coming from your braking system. Again, this doesn’t necessarily mean that your brake rotors are to blame.
Usually, these noises occur because your brake shims are not lubricated enough grease or some other formulated lubricant. This will assist the shims in aligning the caliper and pads properly while reducing friction.
Just apply a thin film of grease to each shim if they have not already been lubricated. Never apply grease to the front of the brake pads!
Why Do Some Brake Pads Have Shims?
A lot of newer brake pads come with the shims already attached to them. So, if you are trying to replace your brake parts, there are brake kits available which contain both the pads and shims together.
In other kits, the shims will be separate from the pads and they will include adhesive backings that let you attach the shims to the pads. If you are new to brake pad shim installation, then you should purchase the brake pads which have the shims already attached.
Types of Brake Pad Shims
There are a few main types of brake pad shims that serve slightly different functions:
Rubber shims are very common and placed between the brake pad and brake caliper piston. They are made of flexible rubber or rubberized synthetics.
The natural flexibility of the rubber helps to insulate the pad from vibrations and noise that would otherwise emit from the metal components rubbing together. Rubber shims range in thickness, but typically come in around 0.5 mm to 2 mm thick.
Metal shims also go between the brake pad and piston. However, these are made of thin sheets of steel or aluminum, making them stiffer than the rubber variety. Metal shims can be coated or uncoated.
The thickness and coatings applied to metal shims affects their insulating capabilities. Thicker shims around 1.5 mm dampen more noise and vibration. Coated shims also help to reduce friction between the metal parts. Different vehicles call for specific configurations to tune the braking performance.
Finally, there are insulation shims that attach to the brake pad backing plate itself. These help dampen vibrations emitting from the pad surface by adding mass.
Insulating shims come in materials like fiberglass or rubberized synthetics around 3-5 mm thick. Some high performance pads have them integrated into the backing plate.
Can You Reuse Brake Pad Shims?
In most cases, yes, you can reuse old shims as long as they are in good condition. You’ll want to clean them off with a little bit of brake cleaner and a rag or paper towels before attaching them to the new pads.
Symptoms of Bad or Missing Brake Shims
There may come a day when your brake shims end up wearing out or deteriorating from excessive use. Once that happens, you will notice some strange symptoms occur. In case your brake pads are missing shims, the same symptoms will apply.
#1 – Brake Noise
The main symptom, of course, will be a lot of loud squealing or squeaking noises coming from your brakes each time you step on the brake pedal. If you recently installed new brake pads and you’re getting squealing noise whenever you are braking, double-check to make sure you’re not missing the shims.
#2 – Pulsating Brake Pedal
You may also notice a pulsating brake pedal anytime you press your foot up against it. This is because faulty or missing brake shims are causing misalignment between the pads and calipers.
See Also: Why Does My Brake Pedal Go to the Floor?
#3 – Poor Braking Response
The worst-case scenario will be a limited brake response, but that should only happen if your brake pads are not able to sufficiently access the brake rotors. This is due to the brake pads not being properly aligned with the brake calipers.
Because of this, the brake pads cannot adequately interact with the brake rotors to slow down the vehicle in time. On top of that, this can also wear out your brake pads and calipers quicker than normal.