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Brake Discs - Rust Area

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Hi all,

The CTS failed it's MOT the other week, bit of a suprise! In summary.....brakes, brakes and errrr...brakes! All sorted now - clean up all around and new pads on the rear. They thought a caliper had seized up on the rear and would need replacing, but it was fine.

Looking more closely at it now, is the size of the area I have rust showing normal for the rear disc? Image here.


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Hi Morgie

The picture looks normal. The areas of rust are the "Unswept" part of the disc that the pads don't contact with and nearly always corrode.


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Had a VW Derby fail an MOT cos of rust on the outside of two front disc where the pads dont touch.

Try to reason with Garage as this being normal but they would not shift.

They they thought they were getting extra wok then they were disappointed.

I brought new pads and discs and fitted them myself. And had them retest at a discount.

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Thanks for the updates - paranoia over! Just to calrify, it wasn't the rust that caused the MOT failure - just something I've been paying more attention to since.

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The rust is not that important, it can be cleaned off quiet easily with a small angle grinder if you remove them from the car first.

Some Totoya dealers used to skim the discs clean for you as part of a service.

What is important is flatness of the surface the pad touches and the thickness of the disc measured on the clean area.

Its usually stamped on the discs or drums as the minimum thickness.

Too thin and the discs can distort so you then get wobble on braking.

Try using the local councils MOT service, ( all taxis have to be checked by them ) they can only test your car, not do any repairs on them , so you get a good unbiased report.

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On my old Rover 214, every so often I'd tap the edge of the disc with a small hammer to chip off the flaking rust (gently tho).

Just a shame that in later years, the MOT garage had to do the same to the bodywork too.

Biodegradable cars, eh?

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Just inputting my 5c...i know how you feel morgie...i replaced all 4 discs and pads with Blueprint parts not so long back...and i'm sure i mentioned this problem in my own thread at the time...within a week they looked as if they'd been on the car for a year lol...they started to rust beginning with a light orange tarnish to a solid brown...a mechanic mate of mine stated i should've painted them and laquerd them...thats the parts that the pads don't touch that is...just so they stay looking newer for longer...but after all the work i went through fitting them and having to deal with partly siezed callipers etc...there was no way i was taking them off lol...so long as you can brake as normal...let it be mate!

Sammy :flowers:

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