Removing the Mystery from Brake Pad Bed-In

by Matt Weiss of StopTech and James Walker, Jr. of scR motorsports

In order for any brake system to work optimally, the rotors and pads must be properly bedded-in, period. This process can also be called break-in, conditioning, or burnishing, but whatever terminology you choose, getting the brakes properly bedded-in and keeping them that way is critical to the peak performance of the entire brake system.

However, understanding why the rotors and pads need to be bedded-in is just as important as the actual process. If one understands what is happening during the bed-in process, they can tailor the process to specific pads, rotors, and/or driving conditions. For this reason, we present this generic bed-in overview pertaining to all brake systems, but follow with links to application-specific bed-in procedures to fit most every set of circumstances.

What is brake pad “bed-in” anyway?

Abrasive friction and adherent friction

There are two basic types of brake pad friction mechanisms: abrasive friction and adherent friction . In general, all pads display a bit of each, with abrasive mechanisms dominating the lower temperature ranges while adherent mechanisms come more into play as pad temperature increases. Both mechanisms allow for friction or the conversion of Kinetic energy to Thermal energy, which is the function of a brake system, by the breaking of molecular bonds in vastly different ways.

The abrasive mechanism generates friction or energy conversion by the mechanical rubbing of the brake pad material directly on the rotor disc. In a crystalline sense, the weaker of the bonds in the two different materials is broken. This obviously results in mechanical wear of both the pad and the rotor. Consequently, both pads and rotors are replaced when they are physically worn to their limit and are too thin to endure further service.

The adherent mechanism is altogether different. In an adherent system, a thin layer of brake pad material actually transfers and sticks (adheres) on to the rotor face. The layer of pad material, once evenly established on the rotor, is what actually rubs on the brake pad. The bonds that are broken, for the conversion of Kinetic to Thermal energy, are formed instantaneously before being broken again. It is this brake pad-on-transferred brake pad material interaction on a molecular level that yields the conversion process.

With the adherent mechanism there is much reduced rotor wear as compared to abrasive mechanism, but it's not a free lunch – pads now become the primary wear element in the braking system. And even though rotors are not mechanically worn down with adherent systems, they still will need to be replaced on a regular basis due to cracking reaching a point of failure if they are exposed to intense, repetitive thermal cycling. This is why race teams throw out rotors that are actually as thick or thicker than when they were brand new. It's due to the an adherent brake pad transfer layer!

The all-important transfer layer

As stated above, the objective of the bed-in process is to deposit an even layer of brake pad material, or transfer layer , on the rubbing surface of the rotor disc. Note the emphasis on the word even, as uneven pad deposits on the rotor face are the number one, and almost exclusive cause of brake judder or vibration.

Let's say that again, just so there is no misunderstanding. Uneven pad deposits on the rotor face are the number one, and almost exclusive cause of brake judder or vibration.

It only takes a small amount of thickness variation, or TV, in the transfer layer (we're only talking a few ten thousandths of an inch here) to initiate brake vibration. While the impact of an uneven transfer layer is almost imperceptible at first, as the pad starts riding the high and low spots, more and more TV will be naturally generated until the vibration is much more evident. With prolonged exposure, the high spots can become hot spots and can actually change the metallurgy of the rotor in those areas, creating “hard” spots in the rotor face that are virtually impossible to remove.

Bedding fundamentals

In general, bed-in consists of heating a brake system to its adherent temperature to allow the formation of a transfer layer. The brake system is then allowed to cool without coming to rest, resulting in an even transfer layer deposition around the rotor circumference. This procedure is typically repeated two or three times in order to ensure that the entire rotor face is evenly covered with brake pad material. Sounds easy, right? Well, it can be if you have the proper information.

Because the adherent temperature range for brake pads varies widely (typically 100°F-600°F for street pads and 600°F-1400°F for race pads), each bed-in needs to be application-specific. One could try to generate a one-size-fits-all procedure, but too little heat during bed-in keeps the material from transferring to the rotor face while overheating the system can generate uneven pad deposits due to the material breaking down and splotching (that's a technical term) on to the rotor face.

In summary, the key to a successful bed-in is to bring the pads up to their adherent operating temperature in a controlled manner and keep them there long enough to start the pad material transfer process. Different brake system designs, pad types, and driving conditions require different procedures to successfully accomplish the bed-in. The recommended procedures below should provide you with the information you need to select the bed-in procedure appropriate for your application.

For break-in procedure, see Stoptech's recommended procedure for Bedding In Performance Brake Systems.

Part No Applications: NMB1020, NMB1025, NMB1100, NMB1200, NMK3202, NMK3204, NMK3216, G2NMB2025, G2NMB2026, G2NMK2000, G2NMK2002, G2NMB2022, NMB2006, NMK3001, NMB2004, NMB2015, NMB1210

Article Date: Jun 23, 2008
Car Accociations: NEW_MINI
Hits: 533

Order and Shipping Information

Worldwide Shipping Charges
Shipping Address Policy
Worldwide General Shipping Information
Shipping Schedule
When Will I Get My Order?
Entering APO/FPO Addresses
Backorders

World-Wide Shipping Charges

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  Backorders

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We will match the published price of any US supplier* -- even their current sales prices! If you find an item advertised at a lower price, make a notation in your online order, call or email us your price match request (see terms and details below). We'll sell you the SAME item at the SAME price! If you've already purchased the item from us, we'll even price match (for store credit only) as long as you contact us with your request within 10 days of placing your order.

This offer is restricted to identical items offered for sale in writing or on the web. When making your price match request, you must provide us with a link to the competitor's Internet URL for the item, a copy of the written ad or written quotation, which must include suppliers part number, description and price.

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We may choose not to price match in some cases; here are some reasons why:

• The competitor's product is not an exact match (identical manufacturer & model) with ours.
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* Qualified U.S. Suppliers are established businesses that routinely and regularly sell the item to be matched from an established physical storefront or warehouse.

While we endeavor to maintain the accuracy of item availability, descriptions and availability, we reserve the right to correct errors. We reserve the right to choose not to honor this offer.

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BACKORDERS

We endeavor to stock most of the items we sell. For Classic Minis, parts are frequently in limited supply and are difficult to keep on hand. the automatic shipment notification email you receive will identify backordered items and indicate the approximate date we expect to receive the item at our warehouse.

Be sure to contact us if you wish to cancel your backorder to avoid unnecessary shipping and restocking charges once the item(s) you’ve ordered is shipped.

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