"Running-in" brake discs

[SurreyGuy]

I've just changed the front brake discs on my car and the instruction leaflet stated that I am to avoid heavy braking for the first 200 kilometres - why?

T.I.A.

[sigma]

The brake disc will not have a smooth flat surface as they have worn over time where as the new pads will be. Until the pads have worn in they will not be 100% efficient.

[Prangy]

^ sigma is correct, it will also stress the brake assembly as the disc will not be bedded in correctly.

[SurreyGuy]

Thanks folks.

The brake discs felt pretty smooth to me and I can't see why new discs would be rough, but I'll accept what you've told me.

Thanks again.

[Toureman]

Whatever you do, do not accept everything you read on here,

New brake discs will have a perfectly smooth surface !

You should also fit new brake pads at the same time.

The 200 miles where you should not break heavily is to allow any bedding in and also to make sure you do not warp the new discs by overheating them.

[SurreyGuy]

Thanks Toureman

I did also fit new pads and have been braking gently, so I should be OK.

[sigma]

My apologies, I misread the question and answered as if you meant new pads not discs.

[SurreyGuy]

No probs sigma.

Although I'm still puzzled as to why the discs would be more susceptible to warping within the first 200 kilometers than after that point, but I'll not worry about that! :o)

Thanks all!