Warped disc brakes - again

[oscarisapc]

I have just had a warning from the MOT centre that my front discs were warped. W203 320cdi estate - big heavy car. They quoted a figure of 16% (not sure entirely what that means) and said that 25% would have been an MOT fail. So I complained to MB who had installed completely new discs and pads (front and back) only in April this year and, fair play, they have replaced the front discs and pads free of charge. However, one of the really good things about this forum is the wealth of knowledge of members, and I was intrigued to see a post (thanks Will) referring to a website where a motor engineer with a racing background claims that there is no such thing as warped discs and that the problem is almost entirely due to improper use of severe braking before the pads have properly broken in, leading to the deposition of cementite on the surface of the discs which in turn leads to differential braking function and irregular wear.
StopTech : Balanced Brake Upgrades
This seems to be an entirely plausible explanation - I have always been unconvinced that modern technology could produce brake discs that are unable to stay flat.

I am trying to break my new brakes in with more care - avoiding sudden stops (fortunately not had to do an emergency stop yet) and also avoiding cooking the brakes by taking my foot off the brake as soon as the car stops and using the "other" footbrake whenever necessary. What do others think? Am I wasting my time? And if not, is there any reason why MB don't provide any break in instructions when replacing discs - and for that matter is there any breaking in that could be done at the dealer before releasing the car to the customer? It might be more expensive but could be offset against the cost of replacing "warped" discs under guarantee.

 

[Will]

Hi there,

Glad you've got the discs sorted at the moment and that the post was useful.

A couple of points :-

I haven't really had many sets of discs/pads replaced at dealerships, but on a couple of other cars that I drive/have driven (non-MB), when they've been serviced and had new brake parts there was an advisory note (hanging from the rear-view mirror IIRC) to advise against harsh braking for the first few miles. Perhaps it varies from dealer-to-dealer, but it seems unusual for MB to not at least advise the customer of this?

I think you're also quite on the ball WRT holding the brakes on for a while after a brisk stop. Out of habit, for years I tend to avoid this. If I've been slowing down heavily I always try and creep a few inches forward if I've been stopped for more than a few seconds. Never suffered from any disc problems on dozens of cars - perhaps a co-incidence but I believe that some mechanical sympathy does help.

Once they're bedded in I'd just avoid sitting with the front brake clamped strongly against the disc after heavy use when the brakes will be very hot

Will