1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

Are these marks on the rear rotor cause for concern?

Discussion in 'Suspension, Steering & Brakes' started by Arzaam, Apr 16, 2018.

  1. Arzaam

    Arzaam Senior Member

    Messages:
    645
    Likes Received:
    39
    Joined:
    Oct 13, 2014
    Location:
    Pakistan
    Your Mercedes:
    W203 2002 c180
    What are these marks on my rear rotor? Pitting? It’s only on this one rotor
    It has 50 k miles on it
    I measured the rotor thickness and it’s 20.1mm and service manual says minimum allowed is 10.4mm but I measured using a vernier caliper and given the lip can I reply on this reading? how would you measure with a micrometer screw gauge? as mine only goes up to 10mm max
    rotor still has a lip

    Any harm in driving like this?

    IMG_3361.jpg IMG_3362.jpg IMG_3363.jpg
     
  2. oigle

    oigle Senior Member

    Messages:
    2,768
    Likes Received:
    127
    Joined:
    Mar 15, 2005
    Location:
    Redcliffe, Queensland, Australia
    Your Mercedes:
    Currently 2003 ML270. 2012 Nissan Maxima 250SL.
    No - you can't use a vernier. A suitable micrometer is the only way - get a bigger one. I personally wouldn't be too concerned about your marks. They are small rust spots which would disappear in time with usage as the disc wears down. They won't cause you any problems.
     
    Arzaam likes this.
  3. John Laidlaw

    John Laidlaw Senior Member

    Messages:
    15,630
    Likes Received:
    3,446
    Joined:
    Nov 15, 2013
    Location:
    Wirral
    Your Mercedes:
    W212 E63 ///AMG V8 Biturbo Volvo XC90 2018
    As above just iron contamination which will come off
     
  4. OP
    Arzaam

    Arzaam Senior Member

    Messages:
    645
    Likes Received:
    39
    Joined:
    Oct 13, 2014
    Location:
    Pakistan
    Your Mercedes:
    W203 2002 c180
    thanks will measure with a proper size micrometer then, it was standing since a month and yesterday I drove it and noticed these marks on that one rotor today
     
  5. steveq

    steveq Senior Member

    Messages:
    156
    Likes Received:
    37
    Joined:
    Jun 9, 2010
    Location:
    Dublin
    Your Mercedes:
    2011 Merc S212 E220CDI Estate; 2011 Merc W204 C220 CDI; 1965 W113 Merc 230SL Pagoda
    Hi,

    You could use a vernier caliper to measure the disk thickness. If you put a coin on each side to the vernier to make it wider than the lip of the disk.
    Take the measurement of the thickness of the disk including the 2 coins.
    Then measure the width of the 2 coins and subtract that from the total thickness. The remainder is the thickness of the disk.
     
  6. AJD

    AJD Senior Member

    Messages:
    4,209
    Likes Received:
    647
    Joined:
    May 31, 2015
    Location:
    Suffolk by the Sea, UK.
    Your Mercedes:
    2012 W204 Sport ///AMG Line 4dr Auto, Obsidian Black, Light Grey Faux Leather
    You would need three hands for that though ;)
     
  7. Naraic

    Naraic Moderator

    Messages:
    9,763
    Likes Received:
    587
    Joined:
    Mar 4, 2010
    Your Mercedes:
    2005 CL500.
    Take a hammer and knock off the lip to allow a Vernier to be used.
     
  8. steveq

    steveq Senior Member

    Messages:
    156
    Likes Received:
    37
    Joined:
    Jun 9, 2010
    Location:
    Dublin
    Your Mercedes:
    2011 Merc S212 E220CDI Estate; 2011 Merc W204 C220 CDI; 1965 W113 Merc 230SL Pagoda
    The hammer option seems to be a bit severe. I suspect the disks are hard but brittle. A few over-enthusiastic blows from a hammer could shatter them. However, that would solve the question mark over their useful life though !!
     
  9. umblecumbuz

    umblecumbuz Senior Member

    Messages:
    3,071
    Likes Received:
    495
    Joined:
    Sep 20, 2010
    Location:
    Wales and Gozo
    Your Mercedes:
    S204 and CLC 204 cdi, other non-Merc machines
    Coins also have lips.
    Not an accurate way of using a precision tool.
    Two flat metal offcuts might be better, but still fiddly.
     
  10. steveq

    steveq Senior Member

    Messages:
    156
    Likes Received:
    37
    Joined:
    Jun 9, 2010
    Location:
    Dublin
    Your Mercedes:
    2011 Merc S212 E220CDI Estate; 2011 Merc W204 C220 CDI; 1965 W113 Merc 230SL Pagoda
    Just measure the thickness of the coins, lips included.
    Once the measurement of the coins on the disk and then off the disk is consistent it is sufficiently accurate.
     
    LostKiwi likes this.
  11. LostKiwi

    LostKiwi Senior Member

    Messages:
    13,399
    Likes Received:
    4,927
    Joined:
    Aug 25, 2006
    Location:
    Midlands / Charente-Maritime
    Your Mercedes:
    '93 500SL-32, '01 W210 Estate E240, 02 R230 SL500 (Malcolm Spec), 04 Smart Roadster Coupe
    Exactly my thought. as long as the caliper jaws cover the lip on both sides of the coin and you mark the coin to measure the same point across the diameter the lip becomes irrelevant.
     
  12. OP
    Arzaam

    Arzaam Senior Member

    Messages:
    645
    Likes Received:
    39
    Joined:
    Oct 13, 2014
    Location:
    Pakistan
    Your Mercedes:
    W203 2002 c180
    Interesting idea
    What if I use my set of feeler gauges and use one that sits flush with the lip( the lip isn’t that much) and then use that with the vernier calipers?

    But I went out and bought a bigger micrometer and measured the disc with it removed from the car as the shield behind the disc was getting in the way of the micrometer, it came out as 15.6mm which is more than the 10.4mm minimum stated
    I cleaned the spots with some sand paper it seems fine now

    I’ll replace them soon but they didn’t seem that rusty and seem to have enough thickness remaining in line with a 50k non aggressive miles rotor


    My mate reckoned some water splashes must have gotten on it while it was parked in a open garage and those left those rusted maybe
    The sand paper made them hardly visible now
     
  13. Botus

    Botus Senior Member

    Messages:
    2,282
    Likes Received:
    273
    Joined:
    Jul 29, 2014
    Location:
    UK
    Your Mercedes:
    S500/2010/500
    if you aren't putting a 40t trailer on the back and racing down the alps above 140mph they look good for another 20k to me,
     
    Arzaam likes this.
  14. L John

    L John Senior Member

    Messages:
    2,609
    Likes Received:
    395
    Joined:
    Nov 24, 2013
    Location:
    UK
    Your Mercedes:
    W204 C350 Petrol Elegance
    Water splashes only leave a small mark that can be rubbed off with a finger.
    Was the car parked for a long time in the garage? If it's parked with wet disks, the disks will dry off but the part under the pad can stay wet for a long time and rust deeper, especially when there's salt on the roads over the winter.
     
    Arzaam likes this.
  15. Ken_R

    Ken_R Senior Member

    Messages:
    626
    Likes Received:
    161
    Joined:
    Dec 11, 2015
    Location:
    Worcestershire, UK
    Your Mercedes:
    W203 2006 C230 Estate
    Salt on the roads over Winter, in Pakistan!:rolleyes: Do keep up at the back.:)
     
    L John likes this.
  16. oigle

    oigle Senior Member

    Messages:
    2,768
    Likes Received:
    127
    Joined:
    Mar 15, 2005
    Location:
    Redcliffe, Queensland, Australia
    Your Mercedes:
    Currently 2003 ML270. 2012 Nissan Maxima 250SL.
    I never park my ML with wet discs. They rust instantly - quite red within 24 hours. Always dry/drive the car for a block or two before parking up.
     
    Arzaam likes this.
  17. OP
    Arzaam

    Arzaam Senior Member

    Messages:
    645
    Likes Received:
    39
    Joined:
    Oct 13, 2014
    Location:
    Pakistan
    Your Mercedes:
    W203 2002 c180
    thanks guys really appreciate every one of the replies its all clear now.
     

Share This Page