chilidip

So the rear rotors on our C230K has worn almost to the indicator line. Is this now the time to change? The car has 40K miles on it.. and I'm reading different opinions. As for performance, I see nothing wrong with the stopping power.. and appears to be working properly.

e1000

What do you mean "indicator line"? Your rear rotors should last quite a while, like 60 or 70k miles.

LILBENZ230

My rear rotors are fine @ 95,500. They had new pads at 76,000 and were checked.

chilidip

Actually, that's what the dealer told me.. BS?

e1000

ask him what the minimum thickness is, and what thickness the rotor is at now.

chilidip

Hmmm.. I have a digital caliper so I'll measure. By any chance do you know what the minimum thickness is?

ncmudbug

You may have found out already that a dial caliper probably doesn't work well for this because usually there is a ridge along the outside of the rotor where the pad doesn't rub.

I've never hear of an indicator line on rotors which is not at all to say they don't exist. Often, the minimum thickness is cast into the non wear surface in the center of the rotor. Where is this indicator line? It sounds very handy.

Beepbeep

Never heard of a brake rotor wear indicator either...I'm also intrigue by this. All I know is the brake pad wear indicator that will touch the rotor once the pads are thin enough.

chilidip

Ok, I believe the car will be ready later this afternoon so I'll try to get information out of him. I do recall him saying there were only 5% of wear remaining.

ncmudbug

Are you SURE he's talking about rotors and not pads? Let us know what happens.

e1000

there's no indicator line on the pads either.

hanknum

Maybe he was referring to tread wear indicators on your tires.

As mentioned before calipers usually won't work too well unless there is a notch on the calipers that you can fit the "lip" of the rotor into. You can check the thickness with a micrometer.

Xhale707

Brakes..

Disc brake pad lining thickness ( MIN ) 1/8 inch (3.2 mm)
Parking Brake lining thickness ( MIN) 1/16 inch (1.6mm)
Parking brake Shoe min thickness 0.040 inch ( 1 mm )


Min Disk / rotor is stated on the rotor some place..

mtnman82

I'm pretty sure there's a wear indicator on the brake pads (metal tab that starts to squeel when you hit the brakes), but not the rotors. Hopefullly that's what he was talking about (and charging you for). No need to replace the rotors when changing brakes unless they're too worn, which is highly unlikely on the rears given your mileage.

e1000

There is absolutely not.

Mercedes uses brake pad sensors. Depending on year, the w203 can have as few as 1 or as many as 3 of these sensors on different pads. There is no indicator line, although looking at the pad and seeing how close it is to tripping the sensor could be seen as an "indicator".

chilidip

It is indeed the rotor he was talking about. My wife actually picked up the car from the dealer who informed me that we only had 5% remaining in rotor life.. sorry he did not a mention indicator line this time. I will need to take the wheel off this weekend to get a visual. Strangely, the pads were still ok.. is it possible for the rotors to wear out before the pads do? Seems really odd to me.

mtnman82

I stand corrected (must be working on too many different cars lately).

The pads should definitely be worn if the rotor is worn (assuming the pads haven't been replaced). If'n it were me, I would have put new pads in along with the new rotors...

e1000

Again, he should give you thickness numbers in mm so you can make a decision yourself.

Original thickness, current thickness, minimum thickness.

ncmudbug

It is very strange that your rear rotors are worn out after only 40K miles. It would even be strange for your rear pads to wear out after only 40K miles. It would be even stranger for the rotors to wear out before the pads which assumes that the pads have never been changed. I find it strange that you would be told that you have x% of rotor life left. That sounds more like what someone would say about pad life, but maybe that's just me.

Do let us know what you find out this weekend!

slammer111

Why bother measuring? Just use this rule: 2 sets of pads for 1 set of rotors. Just changed my front rotors a couple of weeks ago at 101000km, and I'm still on the original rear rotors.

If you want to get nitty gritty, there is a "MIN TH" stamped onto the area between the hub and the part the pads grip onto. My understanding (my SA is awesome) is that the thickness is the minimum WHEN INSTALLING NEW PADS.