Bedding-In & Material Transfer Process

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24 Jan 2025

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Bedding-in is the essential practice of “breaking in” your new brakes for optimal friction performance. Friction is a force resistant to movement between contacting areas.

During the braking system’s material transfer process, there are two types of friction processes that occur. To understand bedding-in and material transfer, we first need to comprehend the difference between these two friction processes: abrasive and adherent friction.

Abrasive Friction Process

When brakes are applied, the pressure and contact between the brake pads and disc generates heat. This causes particles on the material surface to break down. If you were to view the process through a microscope, you’d find miniscule particles of the pad and disc breaking away from the surfaces as they make contact with each other.

Some particles become part of the friction surface of the disc while others cast off and form brake dust. Brake dust sticks to wheels and eventually gets washed down the drain, leading to potential pollution of the environment.

As these particles are sheared from both components, the heat also physically and chemically changes the exposed friction material. This wears down the pads and discs until they’re too worn for efficient performance and need to be replaced.

Adherent Friction (Bedding-in) Process

The particles that become part of the friction surface lead to the adherent friction process, also known as bedding-in, which transfers a layer of brake pad material onto the disc. To ensure continuous smooth braking, the pad material must be evenly distributed across the disc surface.

The transferred material acts like an adhesive, sticking to the brake pad as it’s compressed against the disc. Adherent friction is also less destructive than abrasive friction. It creates a barrier between the components, preventing the disc from being worn down by the pads and vice versa.

This process increases the coefficient of friction, or simply put, how easily the brakes “grab” onto each other. The two forces of adherent friction and pressure can improve stopping distances by up to 20% and extend the lifespan of the brakes significantly.

It should be noted that adherent friction is a constantly evolving process. Heavy braking will remove some of the transferred material from the disc, and this material will need to be replaced under normal braking conditions.

Recommended Bedding-in Procedure

To ensure even material transfer and guarantee flawless cooperation between the components, bedding-in of new discs and pads should be done with care.

During the test drive, the vehicle should be driven at a moderate speed of 30-35mph. Apply the brakes gradually (normally) without reaching a complete stop to initiate the material transfer process.

Repeat this 8-10 times. Each brake application should be less than a minute apart to maintain the necessary temperatures.

When giving the vehicle back to the customer, it’s essential that you advise them to:

• Brake gradually (normally)
• Avoid feathering the brakes
• Avoid sitting stationary with their foot on the brake
• Avoid heavy braking

These practices should be followed for about 200 miles to continue the bedding-in process correctly.

Potential Issues

If the brakes don’t maintain enough heat during bedding-in, the material transfer process won’t occur. On the other hand, overheating can generate uneven pad deposits. Avoid feathering the brake pedal or heavy braking to prevent uneven distribution of friction material on the disc face, which can cause the stick-slip phenomenon.

Once this has happened, continued heavy braking will cause uneven heat distribution. High spots in the friction material will heat up excessively in comparison to the rest of the disc. This will lead to the disc suffering from excessive Disc Thickness Variation (DTV).

Material transfer is a continuous process after the bedding-in phase, and anything that affects this process will cause issues. The biggest cause of uneven material transfer is excessive lateral runout. See our article ‘Understanding Brake Judder’ (coming soon) for a detailed explanation.

It can also be caused by something as simple as poor technique, such as using the brake pedal to slow the car rather than engine braking on serious inclines or repeated emergency-style stops without adequate cooling time. Even a mechanical issue such as a sticking pad, slider, or caliper can affect the even material transfer process. 

NAPA Focuses on Quality

All NAPA Brake Pads are manufactured from the latest generation friction materials and benefit from a high-pressure “ProBed Scorching” treatment to provide superior initial performance and easier bedding-in.

Our partially coated discs are also made to match OE standards. Just like original discs that have coated hubs and edges, NAPA Brake Discs have them too. However, there is no coating on the friction surface, better facilitating the even material transfer process. Without any coating on the friction surface, there is nothing to contaminate the pads and reduce their efficiency.

DRIVE YOUR BRAKING KNOW HOW

Do you have further queries? For in-person support, book a TechMate visit today! Contact the team on 01174 288090 or email [email protected]. All other technical support is available via our expert NAPA Technical Team on 03333 136597 or email [email protected].

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