How to tell if rotor needs to be replaced?? - Mercedes-Benz Forum

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Old 06-13-2002, 08:07 PM   #1 (permalink)
Rohf (Seattle)
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How to tell if rotor needs to be replaced??

While having the supercharger replaced couple of weeks ago, the dealer also informed me that the front brake pads and rotors need to be replaced. <br> <br> How can one tell visually if the rotors need to be replaced? There's no vibrations I can feel or warping I can see visually. Is there a guideline for rotor thickness before it needs to be replaced?<br> <br> I know life expectancy of rotors varies based on driving style (I'm more of a cruiser than a racer), but is 30k miles within the norm of rotor life?<br> <br>
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Old 06-13-2002, 08:14 PM   #2 (permalink)
Brian
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A micrometer...

Usually, you can't tell if a rotor is worn out just by looking at it, except if it's really scored because the pads word down to bare metal. Even severe warpage is hard to see with your eye.<br> <br> Use a micrometer to measure the thickness of the rotor and then compare that to the published spec for the vehicle.<br> <br> I believe that the pads are worn out, but I'd be highly suprised if your rotors were worn out after only 30K miles of normal driving.<br>
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Old 06-13-2002, 08:21 PM   #3 (permalink)
Rohf (Seattle)
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The dealer tech said I have 20% left on my front pads.

I was also surprised the rotors had to to be replaced. Thanks for the info, Brian. If the thickness is similar to the rear rotors, I may keep using the rotors. <br> <br> I'm getting sick of the brake dust -- especially on chrome rims -- so I am probably going to replace them in a week or two. <br> <br> <br> <br>
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Old 06-13-2002, 10:24 PM   #4 (permalink)
SteveL
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The thickness range of the rotor should be stamped on edge of the rotor hub.

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Old 06-14-2002, 03:58 AM   #5 (permalink)
Bruce R.- DC
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Front and rear rotors are very different, so that would not be a good gauge..........

Benz discs are normally good for two sets of pads before they must be replaced. At 35K miles you would have to be pure Hell on the brakes in order to wear out the discs as well as the pads.<br> With only 20% of the pads remaining, they should be around 1/8' thick, take a look............
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Old 06-14-2002, 06:15 AM   #6 (permalink)
LelloSLK
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At 33,000 miles, dealer told me that front pads and rotors had to be replaced. I did not.....

mic the rotors to verify, so I just told them to replace both. They were the original pads. The dealer also told me that one usually gets two sets of pads per rotor. I must be hell in the way I drive :-)
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Old 06-14-2002, 06:30 AM   #7 (permalink)
Hadley
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Rotor and pad life can change quite a bit...

I would expect that pad change at 30k is normal, I've seen people with badly worn rotors at 30k also. The system and materials are designed so that the pads are worn and changed while rotors do not wear out so much. Apart from driving habits, rust and badly worn pads are enemies of rotors (by scoring them).<br>
<br>
One thing though, to my experience one can tell by looking or touching the rotor that it needs to be replaced. The brake pad does not touch all of the rotors face hence the parts of the rotor that do not touch the pad (e.g. the outside periphery) is left high, not-worn, so this can be seen or felt by hand (or at least measured by a micrometer) since the edge created between the two zones is quite distinct. Some mechanics even apply the practice of honing down the rotor flat up to a certain small limit to smooth out the face, but this is obviously not reccommended practice by the factory, and could be a safety hazard.<br>
<br>
To be on the safe side I would change pads before they are totally worn out and the steel backing very quickly scores the rotors which are expensive. I do not rely too much on the brake-lining worn out tell-tale light, although theoretically this should protect the rotors, the pads may be in such a shape to damage the rotors before this sensor is activated.
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Old 06-14-2002, 07:01 AM   #8 (permalink)
Rohf (Seattle)
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Just looking through the wheels this morning, pads looks...

to have 1/8''~3/16'' left. <br> I'm thinking driving down to Midas shop or another to get another opinion on the rotors.
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Old 06-14-2002, 07:40 AM   #9 (permalink)
Loi
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I agree with Hadley... I changed my front brakes about 2 weeks ago

and saw that the pads were worn down to about 1/8' yet the stupid pad warning light never came on. My dealer stated that my pads had 5% left and that rotors would need to be replaced at the same time. I inspected the rotors, didn't see any scoring and the thickness of the rotor seemed ok to me (I could gauge how worn the rotors were (or if they were turned) by looking at how much the outer edges were sticking out relative to the face of the rotor).<br> <br> I do remember reading that MB recommends changing the rotors for every 2 sets of pads you go through. My car is also at the 30k mile mark. I didn't replace the rotors.
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Old 06-14-2002, 07:49 AM   #10 (permalink)
Bruce R.- DC
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The rotors for an SLK 230 are only about $56.00, so it's no big deal really.........

If in doubt, change them out. Jerry has some nice plated and cross drilled discs.
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