Pip1968 said:
Mikee Quickstep said:
I'm a little confused... guidance says:
" MOUNTING NEW PADS ON USED DISCS (rotors)
We do not recommend using discs, which are pre-bedded, or have been used with friction material other than PAGID....
and then..
"If possible, pads should be bedded on used but NOT worn out brake discs"
I'm switching from OEM pads to RS29s. My rotors aren't too bad so probably don't need replacing just yet, but do I bed my pads in on my current rotors or should I look to change rotors at the same time I change my discs?"
In short I think that that procedure is the perfect situation ie buy new Pagid RS29s AND new discs but it depends on how big your pockets are. I stick Pagid RS-29s in for track and then put the OEM pads back in on returning home without any adverse effects.
Whilst not the perfect situation I am sure that the RS29s will bed to the disc to a lesser or greater extent. If you are going to be doing excessive speeds on road or track and perfection is sought then buy new discs otherwise I am sure you will be fine. It may just take a little longer to get them fully bedded in as the original discs will have their own minute grooves/fingerprint that the RS-29 will need to 'mould' to.
Pip
First, a little clarification: grooves in the disc will quickly imprint on the pads during initial use & their presence or absence affect brake efficiency far less than the pad material transfer layer on the disc itself.
Whilst it is perfectly possible to switch around pads like this, for optimal brake efficiency it's not ideal because the transfer layer of one pad material doesn't like mixing with a layer of different pad material. An actual chemical change to the surface of the disc occurs as the transfer of pad material happens; it can often be observed as a slight colour change to a very light gray.
Pad bedding in requires putting a lot of heat into the pad to cook off the resins in the material. Failure to do this correctly will mean that the pedal feels a bit spongy as the pads wear down.
Bedding the disc to the pad can be done at the same time as pad bedding if both pads & discs are new, but due to the heat required for pad bedding, it is preferable to use an old disc that already has a transfer layer of the same pad material. It's easier to bed a new disc with a pad that is already bedded.
Bedding of new discs involves getting them hot enough so that an even layer of pad material is deposited. Failure to do this correctly usually manifests as a vibration through the steering under brakes which is often interpreted as 'warped discs'. Discs almost never actually warp, particularly vented discs as used on our cars; the vibration is caused by the transfer layer only being present on some areas of the disc. If you get this situation, the best way to recover from it is either to take the discs off & use 80 grit emery cloth to remove the transfer layer or to adopt the pad bedding procedure until the brakes feel normal again (AKA, giving the brakes death!).
As I demonstrated to RoRo, you will know when the transfer layer has developed fully because the retardation suddenly increases significantly for the same pedal pressure. Most people who don't fully understand the process use insufficient speed (ie. heat) &/or stop the process too early. That will then lead to problems down the line...
Hope that clears things up