Are these marks on the rear rotor cause for concern?

Arzaam

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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
 

oigle

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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.
 

John Laidlaw

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As above just iron contamination which will come off
 
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Arzaam

Arzaam

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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
 

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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.
 

A.J.

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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.
You would need three hands for that though ;)
 

Naraic

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Take a hammer and knock off the lip to allow a Vernier to be used.
 

steveq

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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 !!
 

umblecumbuz

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Coins also have lips.
Not an accurate way of using a precision tool.
Two flat metal offcuts might be better, but still fiddly.
 

steveq

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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

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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.
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.
 
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Arzaam

Arzaam

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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
 

Botus

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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,
 

L John

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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

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.
 
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Arzaam

Arzaam

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thanks guys really appreciate every one of the replies its all clear now.
 

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