Worn Rotors?
 

A relative and i set about changing his brakes today. And upon seeing his rotors i say he needs new ones, he says he won't buy unless the current ones are unsafe. I'm not sure what the qualifications for a rotors are so i decided to take pictures and ask.

Are these rotors unsafe?

http://www.tigbit.com/images/DSC02673.JPG
http://www.tigbit.com/images/DSC02674.JPG

Measure the wear surface thickness...Mercedes gives a minimum thickness for their rotors.

.As a matter of interest .........http://www.aa1car.com/library/procut3b.htm

Don't condemn the rotor based solely on the fact that there is a lip on it.

As stated above, measure it to see if it is below min thickess. Generally the specifications allow the rotors to wear about 3 mm or so from new to worn before they need to be tossed. If they are close to or below min thickess, replace them. If they are thick enough to survive another set of pads before wearing down too far, then keep them.

I would be much more concerned about the evident rusted-out condition of the ventilation core of the rotors than actual surface condition. This will seriously impact cooling ability and probably balance more than will a worn surface. Absolutely, new rotors are necessary here.

Steve

I'd replace those rotors due to the heavy rust. Thickness is one thing, but rust is another. I have had 2 rotors crack in the circumference around the hub, and in both cases my wife was driving the car. Stepped on brake = loud crack noise, caliper held rotor but rotor separated from hub, so car kept going. Definitely not safe.

If that were my car I'd pad slap it.

One other thing to consider - I worked on a coworker's brakes a few weeks back, 1997 e320. The rotors were worn evenly, not warped, etc. and looked great with no grinding, but had a deep lip like yours. The lip started cutting into the brake pad sensor. He needed new pads anyway, so we put them in, but his warning light was triggered way too early due to the lip cutting into and grounding the sensor. Also, the lip was contacting the pad backing and causing a grinding noise even though the pad had a bit of lining left. I say replace 'em - they don't cost much at FastLane.

The min allowable thickness of a pad is 2mm. On the W210, the rotors are 28 mm new, and I think the min allowable thickess is somewhere around 25mm. This means that each side can have about 1.5mm of material worn away before the rotor reaches min thickness. Thus, a pad worn to the max allowable thickess on a rotor worn to the max allowable thickess would still allow the backing plate to clear the lip of the rotor by .5mm. If the backing plate was contacting the lip of the rotor, I bet they were well beyond min thickess if you were to measure them.

If you use the stock pads and rotors on the W210, the rotors will wear to min thickess with 2 sets of pads.

while the two sets of pads
 

may be a good rule of thumb i bet it is not always true.

the rust in the vents would not bother me in the least.
that is completely normal on un coated rotors.

tom w

Whew!! Not like in the pic! Maybe I'm spoiled in SoCal, where all brakes get a thinly rusted surface, but these brakes don't have rusted vents - The fin ends have completely rusted away! Eventually you'd get disk separation.

Steve

yeah those
 

ends look worse than i am used to (on second look) but i have never heard of one failing from rust.

tom w

Well i got my ruler out and measured from LIP to LIP and it was STILL at minimum (20mm), and i'd say that lip adds ~4mm. Where we've been working to remove the calipers and caliper mount and a pile of rust has collected and it falls out as you spin the rotors. I luckily convinced the tightwallet to order anew though, thanks for the input gentlemen!

Age is just as bad as mileage. Judging by the rust and the fact that they only cost about $40 each I'd replace them. I prefer not cheaping out on important things like brakes.

Our E320 got new rotors (OEM Mercedes) at around 75k miles. However, our piece of junk Ford Explorer (96) just barely got its FIRST set of new rotors at 135k miles, vents were rusted just like in the picture. Brakes were still relatively smooth!