c4004matic

Does anyone know what these holes are for? There are four at 90 degree interval on the E 43. My guess is some sort of sensor.

joshg1001

they are on my E300 too...

My guess is the rotor wear indicator.

c4004matic

Thought about that too, however, rear rotors never wear out, uf you ever have to replace them it because they corroded badly.
Any MB guys willing to chime in?

c4004matic

Bump

vic viper

Wear indicators.

superangrypenguin

Who told you rear rotors NEVER wear out?

c4004matic

Essentially... Rear rotor under normal use last way more than 100k miles Even front rotors can last 100k. Pads of course last a lot less. Aside from corrosion most rear rotors last the life of the car. 70% of the braking is done by the front. I guess if you drive mostly in reverse you could wear them out quicker

ua549

On my BMW I change rotors with the second or third set of pads depending on rotor wear. I don't like to machine turn rotors to smooth out the wear patterns.

c4004matic

Not a bad idea, however 3 pad swaps is no less than 150k for the front brakes! Ive only replaced front rotors in one car an Acura RL. Again rotors can "warp", glaze or corrode before then, all issues that be fixed by resurfacing, but wearing out is rare indeed. Some shops prefer to replace than resurface since its quick and easy but it has nothing to do with wear. If you endurance race your car that is another story.

joshg1001

In my experience, MB dealers never resurface their rotors but advise on changing them out...

superangrypenguin

Agreed

MB dealers will tell you to swap out the rear rotors after replacing the front pads/rotors twice or whatever. They don't want you to resurface so they can make more money on the rotors.

Anyway, my point was that it's wrong to say that rear rotors NEVER need changing. They are a wear item and I have replaced them in my past vehicles for various reasons (wear, weird vibrations coming from the rotors (suspected) etc.

ua549

I get about 25-30k miles on a set of front pads. I'm in a hot climate with very aggressive, congested traffic of 50-65 mph with 1-2 second vehicle spacing. Interstate speeds are higher. Good brakes are essential.

vic viper

Front rotors are also equipped with wear patterns.