BEDDING IN OF PADS UPDATE
Whilst we covered most items in Bulletin 5 regarding the bedding in of brake pads and rotors, we
are still seeing a reluctance of fitters to change their old methods of brake pad bedding in methods.
Customer complaints of brake squeal are subsiding due to improved brake pad materials with
sophisticated formulations, built-in shims, chamfering of the pad face and brake in coatings.
Fitters have adjusted to these changes as well and have followed good practice of cleaning the disc
face in most instances.
One area we are still seeing some reluctance, to change from the old ways, is in the bedding in
procedure.
Some fitters believe the best way to bed in brake linings is to apply the brakes heavily a few times to
the point of an emergency stop. This is a left over from the past, whereby pads where made in a
“green state” and needed the gases burnt out of the pad material, thereby curing the compound.
Nearly all modern manufacturers have cured pads in the box, whereby the gases have been burnt off
already and the old method of bedding-in, only causes the pad material to glaze up, leading to
customer complaints of brake noise and hard pedal feel.
An exhaustive review of recent warranty claims, has shown that this, is the single main cause of
product problems and the education of all is a long term plan, that needs to be accelerated to the
improvement of all involved in the friction industry.
Over the past 5 years there have been more product development and changes in brake pad material
than in the previous 50 years of motoring and common sense tells us all that fitters need to take on
board these technology changes and embrace new methods.
The removal of asbestos as an ingredient in brake material, has been the main driver of all the recent
material changes and development and the importance of changing the bedding-in procedure to
allow for this, cannot be understated.
Our recommended bedding in method as shown on our boxes and fitting sheets is as follows again;-
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).
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