What does it mean to bed-in your brakes?
Date Posted:1 November 2019
Here is a Myth that we hear all the time.
“What the hell, my new brakes are squeaking! They must be defective,” or “I just replaced my brakes a few months ago and they’re already warped? They must be defective!”
As long as you bought your pads from a reputable brand, I can almost guarantee they are not defective or warped. What we have here (for both situations) is that your pads probably weren’t bedded in properly, and a few other factors.
What does it mean to bed-in your brakes?
I’m sure most of you are familiar with this process, but if not: when you buy a set of brake pads, especially higher performance pads, they will come with instructions on or in the box on their specific bed-in procedures. This is a process to “mate” your pads to your rotors with gradually increased heat cycles to create a thin, even film of brake pad material on the surface of your rotor. Let’s get into some detail here:
The brakes on your vehicle work by way of 2 forms of friction - abrasive & adherent:
Abrasive friction: As the pads are pressed against the spinning rotors, the crystaline structure of the pad and even the cast iron of the disc break down, transferring kinetic energy into heat, slowing you down.
Adherent friction: The material of the pad breaks apart and reforms, bonding to the surface of the rotor. This process saps energy away from the turning of the disc, spending it to create that bond, as well as create heat. This is the method of friction that is used to bed your pads to the rotor.
All modern brake pads use both types of friction, just to varying degrees depending on the application. Semi-metallic pads work through primarily abrasive friction, and therefore are tougher on rotors and create more dust in a trade-off that results in the ability to operate effectively at temperatures. Organic and ceramic pads primarily use aderhent friction, the trade-off being that they’re easier on rotors, have better cold performance, and are quieter at the cost of high temperature performance.
Now that we have this established, how does this pertain to the brake judder you’re feeling in your brakes?
Well if your rotors have not been bedded in properly, or they were overworked and lost that bedding, then you can have uneven pad deposits on the surface of the rotor. At first, this just means uneven drip across the surface, causing the pads to grip, then slip, then grip, then slip, etc, and that’s the judder you’re feeling as you brake. At the extremes, if this is not corrected, this can result in uneven rotor wear, and a “warped” rotor.
What about new brakes squealing?
The confusion here comes from the fact that most brake pads come with a metal tab that will rub against the surface of your rotor to indicate that your brake pads have worn down to a certain point (as I’m sure you’re familiar with). So now when most people hear their brakes squeal, they think that they already need to be replaced, but that is often not the case.
What’s happening here is that the conditions are just right for your rotors to vibrate as they pass through the clamping pads, not unlike how a bow being dragged across the strings of a violin work — the main difference is a violin is a lovely sounding instrument, and a squealing brake rotor tends to roar in the key of “ouch.” Not pleasant.
Proper bedding of your rotors can go a long way in reducing this effect, but there are a few other factors that can contribute here. For instance, a layer of rust on your hubs when you install your brake rotors can let them sit against the hubs slightly unevenly, or with some wiggle room, allowing them to vibrate as they turn. Another reason could be your brake pads shifting and allowing play in the contact between the rotor and caliper, allowing the vibration. This can be solved using brake pad shims or some of that brake pad lube they always try to sell you at your local auto parts store.
Source: H&R Suspension
See more technical info here & FAQ's - http://rdabrakes.com.au/page/technical.aspx
See anything you disagree with? Have any questions or suggestions for what myths need busting? Then feel free to contact us to discuss and we would be delighted to chat on the matter.
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