When you buy a shiny new set of brakes, it’s pretty exciting to finally get rid of that horrible vibration, or terrible squeaking. However, if you’re not careful you can be revisiting the problems faster than you think. A customer recently asked a question about why his BMW 740il was shaking when applying the brakes. Almost always, a brake jutter or vibration through the brake pedal is the result of uneven wear on the brake rotors at the end of an improper brake pad bed-in. Either there are variations in brake pad deposits causing thickness changes, or spots on the rotor with different friction.
Many people describes their brakes as “warped”, but honestly it is impossible to generate so much heat on a street car that your rotor changes shape. Often this is well in excess of 1500F (Gray Cast Iron is forged around 1700F), which your brakes will never see. More concisely if you feel a vibration, your brakes are improperly bed-in. Because of the nature of the friction material, there are a few crucial things to keep in mind when you finish your brake job. Read on to learn how to avoid all of that after installing your next disc brake kit.
Why do I have to bed-in my brakes?
The key concept to understand when discussing brake pad brake in (also known as bed in, or burnishing) is that of the transfer layer. The transfer layer is a thin barely visible deposit of brake pad material that is left on the surface of the brake rotor. If you mess this layer up, you will ruin your brake rotors and have to go through the whole thing all over again. The transfer layer is designed to allow the brake pad to grip via adherent friction, which means instead of the pad generating friction directly onto the rotor (abrasive friction), it’s instead gripping onto more brake pad material.
This results in substantially longer life out of the brake rotor, and a smooth, quiet stop. Think of it as ‘seasoning’ the rotor.
Your car’s brakes will experience both types of friction depending on heat ranges. In the lower temperature ranges, straight abrasive friction is the main factor, with adherent friction taking over when your brakes warm up. As you drive away on a cold day, you can take notice to when the brakes warm up and adherent friction takes over. Anyway, the base of the transfer layer is laid down during bed in, which means it is extremely important to be smooth on new brakes during this process. The idea is to make sure the layer of pad material you stick onto the rotor is perfectly even and smooth.
OK, so how do I make sure I bed-in my brakes parts properly?
This takes a little conscious work and finesse, but in generally shouldn’t be too difficult. As mentioned earlier, the key is to be smooth. For a set of pads to bed in on a fresh brake rotor, they have to smoothly be taken to their normal operating temp range for the first 100 or so miles. For standard street pads, that’s around 100F-600F. Racing pads are generally closer to 600F to 1400F.
A General Brake Pad Bed-in Procedure
There are a few differing schools of thought, but I have personally done many brake jobs and have ruined my fair share by reading bunk info on the internet. All brake pads are different, and some pads will love being repeatedly clamped down on from 60-10mph when new. Most will NOT. When going for your first drive, be mindful of your brake parts while driving on a fresh brake job, especially when coming off the highway. Try to slow down a little bit before getting to the end of the ramp to avoid uneven pressure or jabs of the brake pedal at this critical time. This does not mean don’t use your brakes, just go easy on them as the first transfer layer is applied. The transfer layer will not form without adequate heat.
Try your best to never stop and hold the brakes when the rotor is hot in this first phase. If you get caught out by a yellow light, try to get through it without emergency stopping. If you find yourself in the situation of coming down from speed to a complete stop, holding the brakes onto the stationary rotor can leave an uneven deposit in the transfer layer, eventually ruining your bed-in.
Over the next 100 or so miles, you can begin to use your brakes closer to normal, as by now hopefully a nice even layer of pad material has been deposited on the brake rotor. At the end of this phase you can begin the finalization process if you are a perfectionist. Some manufacturers have specific bed in procedures to use, which we have listed below. If you don’t see your new brakes below, follow the above procedure.
Bosch QuietCast Brake Pad Bed-in
This is what Bosch has to say about their QuietCast Brake Pads: Find an area that will allow you to safely stop the vehicle 5 times. Accelerate to about 40 mph then down to 10 mph. Allow 30 seconds between brake applications. Apply moderate brake pressure and reduce your speed to 5-10 MPH. Repeat this procedure about 4 times without bringing the vehicle to a full stop. The idea is to heat up your brake pads and rotors smoothly. Lastly, do another 5 stops to 35 mph down to 5 mph without completely stopping to let the brakes cool.
During the bedding procedure try not to rest your foot on the brake pedal at a complete stop when the pads or rotors are hot. This may cause brake judder as a result of friction material building up in one spot.
EBC Brake Pad Bed-in
This is as per EBC’s instruction from their website: On a QUIET ROAD in safe traffic apply the brakes and slow from 60 to 10 MPH five times in a row. Then drive slowly for a few minutes if safe to do so to allow the brakes to cool. Try to avoid coming to a rest whilst the brakes are heated. A smell may be noticed from the warm brakes, this is normal. Repeat this procedure a second time after the brakes have TOTALLY cooled down. EBC pads get better with miles. Even after this bed in procedure it can take up to 1500 miles before the pads are at their best.
It is important to note here that EBC brakes come with a special bed-in coating that works a little differently than standard brake pads. Taking upwards of 1500miles of driving to fully bed-in, the result is a set of brakes that should last far longer than a normal set of brakes and rely mostly on adherent friction rather than abrasive. The downside is that you will end up with a longer bed in phase with more brake dust than standard pads during that phase.
Akebono Brake Pad Bed-in
Akebono actually does not specify a break in procedure with their pads, champion their specialized formula to be good and ready out of the box. Although it is true Akebono is one of the best OE style brake pads on the market, I would still use caution when installing to avoid accidental errors. Follow the general procedure above when installing new brake pads.
Jurid/Bendix Brake Pad Bed-in
Other manufacturers have a variety of similar techniques, like Jurid (Bendix), the OE manufacturer for several European brands such as Mercedes and BMW. The dealer will do the initial bed in for you using the 30/30/30 method, outlined like this: Perform 30 stops from 30 miles per hour with a 30-second cooling interval between stops. These stops will be performed at a decelerating rate of 12 feet per second or less. This means that it should be a gentle easy stop.