Squealing or squeaking brakes are a common occurrence when you’re at the track, but when you’re sitting in peak hour traffic on your way to work or in the city for a night out, the high pitched squeal can not only be annoying but even a little embarrassing!



Common Causes of Squealing Brakes

1. Worn Brake Pads

Squealing brakes can occur for a variety of reasons, with the first and foremost being worn out brake pads. Most brake pads have a small metal finger on the side of them which protrudes about 2mm past the backing plate. Once your brake pads have worn out, the metal finger begins to contact the brake disc. This results in that high pitched squeak we’ve all heard at one time or another. The manufacturer does this so that you’re prompted to have your brakes looked at and changed.


how to tell when brake discs are worn



2. Glazed Brake Pads

The other very common cause of squeaking brakes is the pads becoming ‘glazed’. All brake pads are constructed with an optimum operating temperature range. A good road pad that would be well suited to commuting to and from work or in start-stop traffic would have a low operating temperature (approx. 0-300 degrees Celsius). Performance orientated pads operate around the 400-800 degrees Celsius range, while dedicated race pads operate from 1000 degrees Celsius and up.


When a brake pad is forced to work beyond its ideal temperature range, this can lead to glazing. The brake pads material begins to break down and crystallise or harden. This results in a surface of very similar hardness and very low friction coefficient contacting each other, producing that same squealing noise. Performance brake pads are typically made of a different compound with a higher friction coefficient. This is why they are prone to squealing at low temperatures and are known for being harsh on brake discs.


Hot performance brakes


During this glazing process, the brake pads friction material can break down causing the friction material to adhere to the discs surface. This results in a pulsating brake pedal when slowing from speed as the discs typically flat surface now has high and low spots. Contrary to popular belief this is a common cause of brake run out, and as long as your discs are not below their specified minimum thickness they can be machined or cleaned to rectify this.


Glazed brake discs



3. Stones/Contaminants

A less common cause of brake squeal (although not uncommon) is when small stones/contaminants become stuck between the brake pad and disc. It’s easily fixed by quickly removing the pads and making sure they are free of grit. However, if you leave it unattended, this can result in the stone/contaminant cutting a groove into your disc as it pushes into the disc itself.


So there you have it. An in-depth look into the reasons why your brakes may be squeaking. Think it might be time for a tune-up? Head on over to Spares Box and check out our range of brakes and our Mid-Year Mega Sale! Saving up to 20% off!



Brake Shoes Explained


Brake Shoes are a major component of the Drum Brake System, one of the earliest braking systems to appear in automobiles. A Drum Brake is simply a large metal barrel or “Drum” that rotates with the wheel as part of the hub assembly. When you apply pressure to the brake pedal, hydraulic cylinders or pistons force the Brake Shoes (which sit internal to the drum) against the inner surface of the drum, creating friction and therefore slowing the vehicle. Brake Shoes often serve multiple purposes, not only as the main brakes, but as the vehicles handbrake as well. Vehicles often have a cable attached to one of the Shoes, which is levered by the handbrake within the car. Even nowadays a Drum Brake is often used within the conventional Disc Brake to act as the handbrake.


Drum Brake Mechanism


Contrary to popular belief, Drum Brakes are very effective due to their “self energising” action. As the first edge of the Brake Shoe is pushed into the spinning drum, the downward motion pulls the rest of the shoes surface against the drum. For this reason almost all Brake Shoes have what is known as a leading and a trailing edge, where the liner material is closer to the edge of the backing plate on one end than the other. This needs to be observed when replacing your Brake Shoes.


Left Rear Brakes


Drum Brakes vs. Disc Brakes


The achilles heel of the Drum Brake is its heat retention. The thick metal drum and shoes retain an enormous amount of heat, and with little to no airflow over the operating parts, they cool slowly. This is one big disadvantage in motorsport that lead to the eventual rise of the Disc Brake.


The other disadvantage is maintenance. While a conventional Disc Brake is self adjusting, Drum Brakes require adjusting to remain even. As the proximity of the shoe-to-drum can be adjusted on each corner, incorrect adjustment can lead to the car pulling left or right when braking. Uneven wear due to leaking cylinders or broken adjusters can lead to uneven adjustment and an ineffective handbrake. Similar to Disc Brakes, as Drum Brakes wear they leave behind a dust. This dust is allowed to collect within a Drum Brake causing harshness and noise.


How Brake Fit Together


Can I replace my Brake Shoes myself?


The replacement of Brake Shoes can be very tricky and tedious depending on your car. Your first time changing them will likely end in many curse words and throwing of spanners. They rely on a series of pins and high tensile springs to operate correctly, all of which need to go back exactly as they came out and with the correct adjustment. If you do decide to give it a go, leave yourself plenty of time. If you can get the assistance of a friend who has done it before we highly recommend it! Always wear goggles and hand protection, as the springs can be merciless when (and they will if you’re inexperienced) they fly off in any which direction at 100 miles per hour. Always do one side at a time so if you get stuck you have another side to reference. And just incase you can’t remember how the Brake Shoe went together, it pays to take a photo beforehand.

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