Surface cracks on brake discs

[jon-]

I recently had my track car MOT'd. The discs have seen a few trackdays, and in that time gotten rather warm so have a fair few (read hundreds) or hairline fractures on the surface of this disc.

Now, the MOT tester told me he should fail me for them, but I managed to get them down as an advisory as it is my understanding surface cracks are really only an issue with aesthetics. The discs aren't lipped, are hardly worn, and still work perfectly.

I'm sure there will be plenty of contrasting opinions on such a topic, but if anyone is in the know your opinion would be appreciated.

Thanks

[davido140]

I'd probably get them replaced if I were you,

Rather a bill than an exploding disk...

ETA how do you know they are only on the surface? you've no idea how "deep" into the disk they go, they will only get worse too.

Edited by davido140 on Tuesday 7th April 16:22

[mat205125]

Any chance of some close up shots of the faces of these discs.

Are they drilled discs? Cracks propogating from the holes can cause failures in extreme cases.

[morgrp]

davido140 said:

I'd probably get them replaced if I were you,

Rather a bill than an exploding disk...

+1

Serious accident if a disc explodes - MOT tester should have failed that in my opinion - He is now running the risk of liability if you were to have an accident...

[jon-]

morgrp said:

davido140 said:

I'd probably get them replaced if I were you,

Rather a bill than an exploding disk...

+1

Serious accident if a disc explodes - MOT tester should have failed that in my opinion - He is now running the risk of liability if you were to have an accident...

The discs will be replaced as the brake setup is being worked on, but I still don't believe it's cause for concern (waiting for someone to come along with better info though)

[jon-]

mat205125 said:

Any chance of some close up shots of the faces of these discs.

Are they drilled discs? Cracks propogating from the holes can cause failures in extreme cases.

No. They are slightly grooved, but the cracks are in no relation to that. They're all over the discs where it looks like the surface skin has just split a little.

They're all under 2-3cm, nothing huge!

[davido140]

jon- said:

morgrp said:

davido140 said:

I'd probably get them replaced if I were you,

Rather a bill than an exploding disk...

+1

Serious accident if a disc explodes - MOT tester should have failed that in my opinion - He is now running the risk of liability if you were to have an accident...

The discs will be replaced as the brake setup is being worked on, but I still don't believe it's cause for concern (waiting for someone to come along with better info though)

you mean you're waiting for someone to come along and tell you that they'll be fine and you done have to shell out for new disks?

How do you know they are only on the surface and not deeper?

ANY cracks in disks = bad, simple as that, they will only get worse and you're risking a catastrophic failure if you continue to track them.

Same goes for tyre damage, I'm sure you wouldnt piss about and not get a damaged tyre replaced would you..

[jon-]

No, but this is different from a buggered tyre.

I've googled it. It's called heat checking.

The discs do NOT look like this



they look like this

the internet said:

Heat Checking

Heat checking is the appearance of numerous short, thin radial interruptions of the braking surface. Heat checking is a normal phenomena of the disc brake function.
This occurs as a result of the heating and cooling of the braking surface during normal operation of the brakes. Heat checks are not detrimental to the function or the performance of the braking system and no corrective action is required. These will frequently wear away and reform as a result of the normal braking process, however these can progress over time into cracks depending on such factors as, lining/disc wear, brake system balance and how hard the brakes are used.

[mat205125]

jon- said:

No, but this is different from a buggered tyre.

I've googled it. It's called heat checking.

The discs do NOT look like this



they look like this

The large cracks in the first shot will have started as small cracks as shown in between the large cracks in the first shot, and in the second shot

Edited by mat205125 on Tuesday 7th April 16:41

[jon-]

mat205125 said:

jon- said:

No, but this is different from a buggered tyre.

I've googled it. It's called heat checking.

The discs do NOT look like this



they look like this

The large cracks in the first shot will have started as small cracks as shown in between the large cracks in the first shot, and in the second shot

Edited by mat205125 on Tuesday 7th April 16:41

So the moral of the story is keep a close eye on the discs until real cracks form, then discard ASAP?

[gj88]

Just change them now. Is the money worth a possible big accident? I dont think so.

[The Riddler]

Its seriously bad form to risk anything on your braking system, but its down to the op to decide what to do.

After the first few replies he still seemed to be holding out for someone to tell him they are fine. Do yourself and other road users a favour and get them sorted asap!

[thetrash]

They'll be fine. You could get the disks skimmed but it will only take material off the disk that you'd use whilst tracking the car.

Mine used to look the same after tracking my car. Disks would tend to need replacing three or four times a year and they would only crack right through when they were well worn. I've had this happen twice and both times the disks cracked when they cooled down rather than working at track temps.

[skeggysteve]

jon- said:

Not sure I've got the quoting correct -( But the picture of the disc I have got right.

Many years ago I worked in motor racing and I'd say that those surface cracks are nothing to worry about. I have those sort of surface cracks on my current daily hack!
But I suggest that you deglaze (sp) the discs - ie rub the surface with course emery paper and then bed the pads in properly.

[sleep envy]

blimey, if anyone on here is says that they should change them I hope they're not running porsche drilled disks, you'd be changing them every year

ever porsche I've seen has had them to some extent - the disks are fine as long as the cracks don't join up

[snuffle]

yes its a bodge and i dare say someone will prove my test wrong but
tip petrol or thinners over a COLD disc
leave 30 secs
wipe dry
looking closely can you see any solvent creeping out from the marks?
any doubts at all then get new discs and split disc or one that shatters is not funny

for a full list of bodges and their legal disclaimers please contact customer services

[RDMcG]

sleep envy said:

blimey, if anyone on here is says that they should change them I hope they're not running porsche drilled disks, you'd be changing them every year

ever porsche I've seen has had them to some extent - the disks are fine as long as the cracks don't join up

100% on that. After a week at the RIng my car had small cracks coming from the drill holes. I talked to the folks there and they said they were ok for now. When I brought the car back to Canada the dealer reaffirmed that. As you say, if the cracks join then its a problem. I check them regularly and will change them as required.

[jon-]

Thank you for some common sense from the evening brigade

If a disc explodes I'll be sure to post on here so you can all point and laugh, but I am doing to take them off and inspect the rears, which i expect will have gotten hotter.