Brake Disc Cracks

[Tim Falce]

I've noticed some small cracks on my front brake discs. These are all around the centre area of the discs both sides and don't seem to stretch to the edges. Do these need changing or are they OK to use? I've seen people run with far worse but don't fancy having a disc give up especially as I will be at Combe next weekend and speed and braking forces will be high there.

[MGDavid]

I sense that you know the answer you will get; change them! Brakes is not the best item to take a gamble on...

[Tim Falce]

OK, maybe I should rephrase it. I've got little or no chance of getting new discs this week as the manufacturer is incredibly slow at doing anything so if they aren't on the shelf then a delivery date of maybe sometime never will be in order.
The last time I bought any he had them there but it took him ages to cut grooves on them so if it's the same this time I may have to plump for plain ones.

[JamesH]

How deep are the cracks? I presume not right through (that would be very bad)? Can the disks be skimmed in the timescale?

Just did a quick google - its looks like Heat Checking

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.

http://www.juratek.com/support-discs.php



This would probably indicate your disks are overheating.

[Tim Falce]

James thanks for the post, that looks exactly what it is and probably caused by my driving style as I brake quite hard and late. I was having problems with pad glazing until I changed to Performance Friction which has solved the problem, they also don't seem to wear as quickly either. I expect it's all a trade off but I can live with it as long as the car stops OK.

[Jeff 8]

Could you duct air to the discs?

Jeff

[GORDON STREETER]

Tim if they are the ones shown in the picture they can be resurfaced but as they are on bells they are very difficult to "skim" and should be plough ground otherwise you will probably suffer from brake judder.

[Al Weyman]

I would use them but its up to you and BTW why bother with the grooves, with modern brake materials they are not really necessary IMHO and others more knowledgable, The only time I did have a disc crack completly was one that was grooved so I stopped doing it and noticed no performance difference whatsoever and I am pulling up 1400kgs from up to 140mph. Same with drilling, it will promote cracks and is just for show.

[JamesH]

Originally Posted by GORDON STREETER

Tim if they are the ones shown in the picture they can be resurfaced but as they are on bells they are very difficult to "skim" and should be plough ground otherwise you will probably suffer from brake judder.

Hi Gordon,


what's plough grounding? Tried googling but nothing came up.

James

[Al Weyman]

Its plough grinding not plough grounding try typing that in to google and you will have more luck.

[tristancliffe]

Originally Posted by falcemob

I've noticed some small cracks on my front brake discs. These are all around the centre area of the discs both sides and don't seem to stretch to the edges. Do these need changing or are they OK to use? I've seen people run with far worse but don't fancy having a disc give up especially as I will be at Combe next weekend and speed and braking forces will be high there.

We recently replaced the front discs of my car for a very similar reason, although our cracks were much worse. However, Bob Green of BG Developments said that when they were racing GT40s at LeMans they always got these crack - at first they replaced them, but after a while they just ignored them, and never had a disc failure.

So you'll be fine for now, but get a new set on order for peace of mind.

[jerryk]

having studied the photos in detail I think you will be fine as along as you dont take them to a track that has a corner like quarry at castle coombe . the bumps on the straight prior could set up a high frequency oscilation leading to a catastrophic sentripidal destruction curve . nasty

[Tim Falce]

Originally Posted by jerryk

having studied the photos in detail I think you will be fine as along as you dont take them to a track that has a corner like quarry at castle coombe . the bumps on the straight prior could set up a high frequency oscilation leading to a catastrophic sentripidal destruction curve . nasty

Just make sure you have the picnic table and some buns ready for me at Tower then

[GORDON STREETER]

Tim I personally would use them as they are. If you decide to have them ground in the future I can give you a contact number . They don't charge silly money either, I had 4 done and was well surprised.

[Tim Falce]

I'll use them for the time being Gordon, I'm sure if I speak nicely to someone on here he will let me use his surface grinder to do them.

[Notso Swift]

Originally Posted by Al Weyman

I would use them but its up to you and BTW why bother with the grooves, with modern brake materials they are not really necessary IMHO and others more knowledgable, The only time I did have a disc crack completly was one that was grooved so I stopped doing it and noticed no performance difference whatsoever and I am pulling up 1400kgs from up to 140mph. Same with drilling, it will promote cracks and is just for show.

I agree with not drilling, especially these guys who drill sraight through the vane (though some top end stuff has cast holes)
But my experiance with slots has never been negative, but again that is with quality motorsports disks.
The way I see it if guys like the WRC (who must use ferrious brakes) have nuttted it out with AP/Alcon/Brembro/whoever and they do it there must be a good reason. (Gas expansion preventing a barrier being the most often touted)
My car runs to about 140mph as well, though it only weighs 1100kg, but it only has 287mm disks for 15" wheels.

Oh, and I wouldn't bother about those cracks either, but at the end of the day you are the one who needs to 100% happy

[Al Weyman]

I believe the modern generation of pads do not have the gassing problem that the old stuff did hence no need for slots or holes anymore its what I read and what I have found. I think a whole lot of it is so much hype to get you buying. I just use standard across the counter 12" LE1 option discs on my cars and they pull up OK and in fact on my older car I have huge 6 pot Wilwood Grand national calipers and I have to be careful not to lock them up. The most important thing I ever done was fill the system with Castrol SRP fluid and I have never had a brake boil or fade problem since.

[phoenix]

I use Performance Friction pads and I do as I'm told.....

http://www.performancefriction.com/pages/rotors.htm

....so I run grooved discs for better bite. Never had a crack as a result on AP supplied discs: http://www.apracing.com/info/info.as...+Face+Types_39

[Dave Brand]

Originally Posted by Al Weyman

I believe the modern generation of pads do not have the gassing problem that the old stuff did hence no need for slots or holes anymore its what I read and what I have found.

There will always be a possibility of gassing with organic pads, as they still use phenolic resins. Over the years resins have been modified to reduce gassing to a very low level, but the phenomenon known as 'green fade' can still exist - basically, it's caused by the resins completing their curing process the first few times they are brought up to normal operating temperatures. For road pads & some race pads green fade is eliminated by scorching the working face of the pad during production; for non-scorched race pads it's important to follow the bedding-in advice given by the manufacturer.

. . . no gassing with sintered pads!

[GORDON STREETER]

I never have any trouble with the carbon discs on the Anglebox

[Al Weyman]

Yes i was impressed with the claims for the sintered pads on a stand at Race Retro, French I believe they were and they reconned you can get a set to easy last a season of club racing.

[GORDON STREETER]

Originally Posted by Al Weyman

Yes i was impressed with the claims for the sintered pads on a stand at Race Retro, French I believe they were and they reconned you can get a set to easy last a season of club racing.

Just depends how much you use them, a set of carbon metallic pads would last ages on my car. But being quite a light car I don't have to use a lot of heavy braking. I also turn them upside down every couple of races to even out the pad taper so the don't jam up in the caliper.

[Al Weyman]

I think this guy I was speaking to (Chris Schirle??) is a long distance racer and he reconed they would last a very long race! I think the pads were Carbon Morane or something.

[Dave Brand]

Originally Posted by Al Weyman

I think the pads were Carbon Morane or something.

Carbone Lorraine.

[Al Weyman]

I was close :-)