Brake Rotors
 

Will anyone please tell me why MB does not recommend 'turning' old rotors but instead advise 'new' as a replacement only?

I'm guessing, but it could be for any number of reasons.

The rotors don't have much stock to begin with. If turned, they'll have heat capacity below what MB considers acceptable. Even if there was enough stock, the remaining life wouldn't be worth the cost of turning.

Depending on who turns the rotors, they may be warped coming out of the lathe.

Autobahn, 150 mph and you need to slam on your brakes because a little Fiat just pulled into the left lane.

I wouldn't bother turning them discs are cheap.

When you apply the brakes, the rotors wear down along with the pads. Most of the Mercedes rotors barely have 3mm of wear allowed before they reach minimum thickness. From my experience with stock brakes, this is takes 2 sets of pads before the rotors are below min thickness.

For example, on my car, the rotors are 25mm new. Min thickness is 22.4mm (I think). After 1 set of pads, they were worn down to a hair over 23mm. Then pads got replaced and after the second set of pads, they were worn down to almost 21mm thick, which is well below min allowable thickness. At this point the rotors need to be replaced. There was no need to turn the rotors in between pad changes and if I had turned them, any extra material removed would have taken them almost to min thickness after 1 set of pads and made them essentially worthless. I believe at least on a C280, if you use a set of pads all the way down, then turn the rotors, you will not be able to use a second set of pads, the rotors will need to be tossed anyway.

Rotors are cheap and there is no practical benefit to turning them after 1 set of pads. After 2 sets of pads, they will probably need to be tossed no matter what.

There's no reason not to turn Mercedes rotors - other than the reasons mentioned - it just doesn't make much economic sense.

OEM rotors are all about light weight
1) being compatible with the friction material of the pad
2) so pulsation isn't a problem

Also don't use aerosol brake cleaner to clean rotors or pad surface.
Detergent and water applied with a scrub brush is the proper method

Also the proper way to break in new brake pads- thirty slow stops spaced two minutes apart from thirty mph using light pressure.

I copied this from STARTUNED

In over 30 years of messing about with cars, I have NEVER seen a brake rotor turned straight. Every one of those damn machines is crooked. Replace rotors with pads. They're cheap.

Don't know this as fact, but I've read that generally European cars were built for light unsprung weight and rotors were always viewed as "disposable". The early US disk brakes had a lot more meat.

OTOH, I remember buying a set of rotors for a 1980 Chevy Citation for $150 (each!) in 1982 dollars - because there weren't third party mfr's for them yet. So, rotors for these cars (mine, anyway) are pretty cheap.

Brake Rotors
 

Thank all of you took the time to reply, my knowledge base has just taken a giant leap, thanks to this great forum and people like you:) .