Knackered brake disc?

phil675 · 26 Mar 2012 at 16:42

Hey there,

I've been hearing a grinding noise coming from the driver side front brake lately, had a look and it looks like the pad has been digging in to the disc.

Does this mean the disc/pad is screwed? The other side doesn't have any marks on the disc at all.

Liquidfox · 26 Mar 2012 at 16:58

Is there actually any pad left? Or is there a massive lip on the disc? I'd say that's a new set of front pads and discs for you!

phil675 · 26 Mar 2012 at 17:01

There's a fair bit of pad, had them changed 10k miles ago. Bit of a ballache to get the pads and discs done at the moment, what would have caused this?

Firestar_3x · 26 Mar 2012 at 18:33

Drill discs are bad news imho.

Looking at that pic i'd get the discs and thus pads changed.

TRNC · 26 Mar 2012 at 19:47

What???

1 tiny score mark and you lot are condemning the discs to the bin?? Seriously people, there is nothing wrong with them!

Clarkey · 26 Mar 2012 at 20:37

TRNC said:
What???

1 tiny score mark and you lot are condemning the discs to the bin?? Seriously people, there is nothing wrong with them!

Clearly not working properly are they.

Simon · 26 Mar 2012 at 21:49

Might be a trapped stone. Or they just need using properly - give them death.

TRNC · 26 Mar 2012 at 21:51

Clarkey said:
Clearly not working properly are they.

Rubbish.

You cant say from a poor photo if the brakes are working properly or not. A few light scores in a disc could be debris such as stones, or a hard area in the pads - neither of these warrant replacement unless the scoring is significantly worse than that shown above.

danza · 26 Mar 2012 at 21:59

From my inbuilt opto-digital surface comparator and micrometer laser depth measuring device with HD video decoding and analysis capability, I conclude that you might need to do something with your car at some point, including but not limited to brake inspection, air freshener refill or oil level check.

bobuk · 26 Mar 2012 at 22:10

agreeded with Danza, definitely the air freshener...

phil675 · 26 Mar 2012 at 22:12

Thanks for the.. advice guys.

Would it be worth taking the pad off and giving it a clean or something?

danza · 26 Mar 2012 at 22:22

phil675 said:
Thanks for the.. advice guys.

Would it be worth taking the pad off and giving it a clean or something?

Take the pad off and check there's nothing wedged in the groove. You can abrade/descale pads with ~P120 wet & dry which may help if they are glazed.

Firestar_3x · 27 Mar 2012 at 10:26

TRNC said:
What???

1 tiny score mark and you lot are condemning the discs to the bin?? Seriously people, there is nothing wrong with them!

What looks like deep marks around the disc, lip forming on the outside edge, drill hole outer edges chipping away, pad not making full contact with the disc face.

Like i said drilled discs are bad news, i'd change them.

TRNC · 27 Mar 2012 at 10:31

A bit of light pitting and a small lip! Do you work for Kwik-fit or something - they like to tell people to replace parts when not needed.

The only point I agree on is that drilled discs are generally bad news.

Firestar_3x · 27 Mar 2012 at 10:35

He's got a rusty inner arch too....

Overlag · 27 Mar 2012 at 10:40

Need to do a few emergency stops should clean it...

HummuH1 · 27 Mar 2012 at 12:51

Firestar_3x said:
Drill discs are bad news imho.

Why do you think that? I'm sure BMW, Audi, Mercedes, Lamborghini, Porsche and Ferrari and others would be keen to know also.

Firestar_3x · 27 Mar 2012 at 12:54

HummuH1 said:
Why do you think that? I'm sure BMW, Audi, Mercedes, Lamborghini, Porsche and Ferrari and others would be keen to know also.

Drilled holes in the disc offer performance benefits; this is why the above manufactures decide to use them. However it also reduces the structural integrity and promotes cracking and in some cases causing catastrophic failure of the disc through the drilled sections.

danza · 27 Mar 2012 at 12:55

TRNC said:
A bit of light pitting and a small lip! Do you work for Kwik-fit or something - they like to tell people to replace parts when not needed.

The only point I agree on is that drilled discs are generally bad news.

The lip doesn't have to be very big for the disc to need replacing. My CTR discs are nominally 25mm thick, and need replacing when they are 23mm thick. A 1mm lip either side isn't much. The only way to tell if a disc needs replacing through wear is by measuring the thickness in several positions with a caliper/micrometer and comparing with the car manufacturer's spec for minimum thickness.

So the fact is that none of us know whether the disc needs replacing or not. Drilled discs are indeed pretty crap (namely the cheap ones), and grooved ones even more so. Plain discs all the way TBH.

HummuH1 · 27 Mar 2012 at 13:31

Firestar_3x said:
Drilled holes in the disc offer performance benefits; this is why the above manufactures decide to use them. However it also reduces the structural integrity and promotes cracking and in some cases causing catastrophic failure of the disc through the drilled sections.

Interesting. Personally, I think the "promoting cracking" theory is a bit outdated now with most reputable manufacturers casting the discs with the holes in them rather than "drilling" them through a solid disc. I would have thought that also improved structural integrity but don't know tbh.

FWIW I've never had a drilled disc go on me in some 10 years of use on road and track. I've had at least 3 solid discs go in the same time.