KA8

Got an 06 model here with cross/drilled stock rotors. Can these be turned? Or do they need to be replaced with new brake pads? I always wonder this and never got to ask. I've read somewhere you replace the pads as long as rotors aren't warped.

kompressor85

statement rescinded- i was wrong and wouldnt wanna mislead anyone. even though everyone below me states the opposite. haha.

e1000

AFAIK, cross drilled rotors shouldn't be machined. The rotors seem to last about twice that of the pads, and yes, you can replace pads without replacing rotors if they aren't warped.

C230 Sport Coup

'zactly. The rule is replace rotor every other time.
Use a caliper to check thickness.
Last I checked Duval had the best prices on rotors. 90 bucks each for the C32 ones vs. 185 at the closest dealer at the time!

e1000

The 2006 C230 has slightly smaller rotors than the C32. In either case you shoul be able to find replacement rotors at a nearby dealership that aren't too expensive.

Moviela

It is not possible to machine rotors to the specifications required with workshop tools. Drilled rotors are very hard to machine, and require a very talented machinist to do the work. A new rotor is more economical. To determine if a used rotor is suitable for continued use you need about $ 400. worth of precision tools. The first tool you need is a brake disc micrometer. This is a special "mike" that has a very deep throat so you can measure from the outside edge to the center of the friction surface. The contact points of a brake mike are also specialized. The fixed point is conical shaped, and touches the disc at a point. This allows measurement into the grooves made by the pads. The moving side is a ground flat that touches a larger area on the other side of the disc. I use a Starrett No. 1016M. Some people suggest that a caliper is "good enough" to measure. Unless it is a very special caliper, it cannot measure below the ridge formed at the outside edge of the rotor where the pads do not touch it.

Every rotor must have the minimum thickness stamped on it. This is the thinest that the rotor should be to remain safe, and stop the car. If the rotor is exactly at minimum, it should not be used because it will wear below minimum during the life of new pads. Please don't risk brake failure for the price of a rotor.

The next measurement requires a dial indicator and bracket to mount it on the car. This measures the runout of the rotor. This is how much the disc wobbles as it turns. Look for the allowable dimension in the service literature. I find it usually is .015mm, with .025mm being OK. At .050mm you will feel brake judder and have fast wear of the pads. A human hair is about .090mm. Make sure that the hub where the rotor is touching is clean and free of rust or grease. I see cars where a mechanic smears grease on the hub to make it easier to remove next time. This throws the runout off spec, and should be avoided. Any dirt or grit in there will **** the rotor and cause runout. Mercedes uses a damped cast iron for the rotors. Is better than standard gray iron, but is softer and wears out faster when aggressive (Porterfield, Akebone, & ceramic) aftermarket pads are installed.

It is my experience with C class is that the rotors need to be changed about every second set of pads, assuming that the rotor measures up to continued service.