Brake disc corrosion

[mihangel]

Hello I am looking to buy a used Audi. The car I am interested in had a brand new mot and 145 point check completed the day before my test drive.

After test driving I was looking the car over and noticed the front disc had corroded and a chunk missing. should this have been picked up by the 145 point check or even failed it’s MOT?

Thanks for looking

[meatballs]

That looks like the wear indicator to me? Disks have a chunk missing so if they wear down to that level you get a big obvious gap and know they need replacing sharpish.

[Fiammetta]

Those are knackered .
Minimum should be an advisory on the MOT .
Car has been stood unused outside for a while .
Ask for new disks n pads or walk way .
How many miles btw .fwiw ?

For comparison

[mihangel]

46k they replaced the back discs and pads in the 145 point check but not the fronts. Maybe an expensive part and job?

[SuperPav]

Sorry I disagree with the above poster. The “missing chunk” you’re referring to is a machined out section that’s used to balance brake discs - you can see it on the other edge as well.

From the photo it’s hard to tell but it doesn’t look like there is any wear lip, it’s just surface corrosion from being parked up for a while!

In other words, that looks absolutely fine to me from the one photo you’ve provided

[Andy 308GTB]

SuperPav said:

Sorry I disagree with the above poster. The “missing chunk” you’re referring to is a machined out section that’s used to balance brake discs - you can see it on the other edge as well

Great spot.

[E-bmw]

Andy 308GTB said:

SuperPav said:

Sorry I disagree with the above poster. The “missing chunk” you’re referring to is a machined out section that’s used to balance brake discs - you can see it on the other edge as well

Great spot.

Realised that when I saw it as it is obviously that.

Although they are fine for the moment the disc surface isn't being fully wiped by the pads and there is a lip appearing, so. If it was me buying it I would be dropping the price or asking for it to be done assuming the car is reasonably new.

[Sheepshanks]

E-bmw said:

Although they are fine for the moment the disc surface isn't being fully wiped by the pads.....

The trouble is that once rust sets in it rubs the pad away so the rusty bit speads across the disc and you end up braking using an increasingly narrow band, especially on cars that are gently driven and where the pad / caliper sliders stick. The rear face of the disc usually looks worse.

[PhillipM]

Surface corrosion and a piece machined out for balancing/harmonics. They're fine. Stand on the pedal and they'll be shiny.

[DeadCatWalking]

meatballs said:

That looks like the wear indicator to me? Disks have a chunk missing so if they wear down to that level you get a big obvious gap and know they need replacing sharpish.

Ummm, no they don't. Pads have wear indicators. Disks have thickness limits you need to measure. That's balancing machining in the photo.

To the OP, there's clearly about a 1 mm wear lip so 2 mm total loss of material which is the normal disk wear limit on most cars. The calipers are also sticking which is why the pad is not making full contact. Deffo time to replace everything.

[Chris32345]

Fiammetta said:

Those are knackered .
Minimum should be an advisory on the MOT .
Car has been stood unused outside for a while .
Ask for new disks n pads or walk way .
How many miles btw .fwiw ?

For comparison

No where near a mot failure barley worth a advisory that looks to be only a Chunk of the rusted edge that's broken off it's not effecting the disk at all

[DeadCatWalking]

Chris32345 said:

No where near a mot failure barley worth a advisory that looks to be only a Chunk of the rusted edge that's broken off it's not effecting the disk at all

Oh we're going to bring grain crops into this? Wheat if it's a maize of problems just waiting to unleash themselves?

[E-bmw]

Sheepshanks said:

E-bmw said:

Although they are fine for the moment the disc surface isn't being fully wiped by the pads.....

The trouble is that once rust sets in it rubs the pad away so the rusty bit speads across the disc and you end up braking using an increasingly narrow band, especially on cars that are gently driven and where the pad / caliper sliders stick. The rear face of the disc usually looks worse.

Correct, hence why I used the caveat "for the moment" in that.

[Fiammetta]

Chris32345 said:

No where near a mot failure barley worth a advisory that looks to be only a Chunk of the rusted edge that's broken off it's not effecting the disk at all

Never said fail .
Any tester worth his salt , no skin off his nose and not knowing how’s it’s gonna be used until next time will have zero hesitation passing it but writing an advisory on the record “ surface corrosion “ on [ insert relevant disk ] It passed its brake balance / pressure test .
It’s all about covering your arse and accountability these days .

It may appear same station same examiner in 12/12 with same picture .....but with an extra 100 miles on the odometer .= assuming it passes = same advisory can be written .....what’s wrong with that ?