mx5cartalk.com

BEDDING IN OF PADS AND ROTORS
When a vehicle has had both new rotors and/or just new pads fitted, there are two processes or
objectives, to getting the brake system to operate at optimal performance.
The first step is to make sure the disc face is clean of all oils/anti rust or any foreign matter like
previous brake pad material. If the rotors are not being replaced then it is imperative that the disc
is machined prior to the fitment of new pads- without exception.
The second step is heating (not cooking) the brake rotor and pads, to transfer the pad material
evenly, onto the rotor face.
This step involves performing a series of stops, so that the brake rotor and pad are heated steadily, to
allow the transfer of pad material onto the brake rotor friction surface. The friction surface should be
clear of all oils which are used to stop the rotor from rusting before being fitted to the motor vehicle.
Whilst these will be burnt off, they risk transferring and possibly polluting the brake pad material
and will definitely lead to a longer bedding in process. Whilst performing a series of brake
applications to transfer the pad material, care should be taken to not come to a complete stop, as this
can lead to the transfer of pad material unevenly on the disc at the point where the pad comes to rest
on the friction surface.
A typical program of 8-9 brake applications, from 60km down to 10km p/hour, without any cool
down in between would be sufficient. .
For performance pad materials, a further two sequences of ten stops will be required after a cooling
down period between each cycle, to ensure that the pads have reached the required higher operating
temperature to allow for the pad material to transfer effectively.
At all times during the bedding in process, care should be taken to not apply the brakes in a harsh
manner or decelerate from high speeds, as this will corrupt the transfer of materials and lead to
uneven material build up on the rotor surface, which in most instances will require machining to
regain a flat rotor surface for optimal operation (Disc thickness vibration-DTV-which leads to brake
judder or vibration-see RDA/EBC Bulletin #1).
How will I know if they are bedded in?
The two major visual indicators are disc rotor discoloration and machining marks on the friction
surface of the disc rotor.
1) Disc rotor should have a slight bluish tint with a grey tint that indicates where the brake pads
have come into contact with the rotor. Too much heat will cause the rotor face to be
extremely blue and has been overcooked in the bedding in process.
2) If there is still a shine on the rotor surface, then not enough pad material, has been
transferred.
Once brakes have been bedded in, it is also important, to keep them that way. If any brake pad is
used below its adherent operating temperature over a period of time it will slowly remove the
transfer layer on the rotor surface. Standard and especially performance pads, like to be dríven a
little more aggressively every now and then to maintain this pad material, on the rotor friction
surface. Similar in effect to taking a city based car on a country run every now and then and noticing
the change in the exhaust tail pipe color, go from black to grey as it operates at a different
temperature, to what it has become accustomed. Passive use of brakes over an extended period of
time will in effect lead to “unbedded brakes”.