Too hard on the brake disc

[BW]

Any one can look at the attched rotor and suggest me should get them replace or keep to use........

Alcon 370 floating 32mm, SBS double carbon pad, 6 monobloc caliper.

[DavidR]

I replace mine when they do that as the vibrations when they expand become very annoying, and 2 discs cracked completely radially from the centre out...

[SimonS4MTM]

Not sure if that is too much of a problem, this is from a GT car, and they are happy to race with discs like this. They say it is normal fro steel discs in race conditions, so i doubt it would fail catastrophically.

Only a problem as David says, if the vibration gets a problem

[DavidR]

Simon, I have tend to be cautious with discs like these. I have had 2 crack pretty catastrophically, one on a road car, the other on a track car... Both had these fine radial cracks, but had been used for some time after they appeared.

My friends EVO cracked a disc also, having had these smaller cracks appear.

I think with race cars and dedicated heavy track cars, the small cracks are inevitable, although on GT cars, they are likey to replace the disc very often, and the total mileage on a cracked disc will be small. I would have thought that the disc in the photo on the GT car will not be there much longer, it looks like it is due for replacement. I hear also that BMW replace the discs on the M5s used for the Ring Taxis when they crackle as above.

On a road car, the discs are exposed to the corrosive salty road conditions, a greater number of miles and heat cycle, which over time increases the risk of more serious and dangerous cracks.

I change my discs now if I notice the above... Having a disc crack completely is not pleasant

[DaveP]

Ben, how old are the disks ?...I didn't think you'd had them fitted that long ?

[johneroberts]

Nothing wrong with them, just need a deglaze and a bit more careful treatment.
Cheers
jr

[DavidR]

Nothing wrong with them, just need a deglaze and a bit more careful treatment.
Cheers
jr

Huh? Other than they have thousands of cracks penetrating the disc surface. Which tend to get worse the more they are used. That tend to then cause disc failure if left long enough.

There is no "deglaze" in the world that is going to solve those cracks John.

[SimonS4MTM]

Carbon metalic discs such as those on the SLR have the same cracks from almost the first time they are used.

If a GT team is happy to enter a race with these cracks, bearing in mind that a win can cost them £100k's, then why not continue to use them.

Sure a larger crack can develope, but it is no more likely than with a disc without any of those small cracks.

[SimonS4MTM]

I am at Autosport this Thurs and Friday so I will confirm this for you with AP or Brembo

[johneroberts]

Huh? Other than they have thousands of cracks penetrating the disc surface. Which tend to get worse the more they are used. That tend to then cause disc failure if left long enough.

There is no "deglaze" in the world that is going to solve those cracks John

This normal, its somthing to the untrained eye is distressing and i fully understand your apprehension, i have seen much worse condition discs on a competition car.
Cheers
jr

[DavidR]

I still disagree.

From the look of the disc it would appear to have heat checking across the surface. The only definate way to tell is to sand an area to make sure it is not pad deposition, but it looks like thermal stress fractures across the disc face.

Most manufacturers will confirm that heat checking is a sign of excessive thermal stress due to insufficient cooling or a too agressive brake pad compound being used. Heat checking WILL usually become worse if the characteristics of the brake use remain unchanged. They are often the precursors to more serious disc cracks, and I maintain you should be cautious.

It seems the jury is out on the site here, but I would encourage the original poster to send the images to the disc manufacturer and confirm their view. It's easy to be flippant about these things, but it can be a serious issue

Regardless, I would not trust my front brake discs under extreme use if they were extensively checked. I have, as said, destroyed 2 discs under the above circumstances.

Some quotes from motorsport and brake manufacturers....

Post Track Day Rotor Inspection
All disc rotors should be inspected after track day events. This involves removing the rotor from the vehicle and inspecting for heat checking (surface cracking) and severe cracks from fatigue on the pad surfaces. If the heat checking is advanced to the point where the surface cracks are clearly visible, discard the pair of rotors. One ideal method that should be adopted is to have two sets of rotors. One set for track use and one for street use. Changing to your street rotors after a track event encourages rotor inspection. Also, your street rotors can become your next track rotors with the advantage of being bedded in gradually. After the initial purchase of two sets of rotors you are still only replacing one set at a time.

Heat checking: The precursor to cracking. Heat checks are actually surface cracks caused by thermal stress. By themselves heat checks are not a cause for concern but they are a warning sign that the disk is not receiving adequate cooling air and cracks are sure to follow. See also the section "Cracking".

[johneroberts]

I still disagree.

We are all entitled to our opinions DavidR
But i personally would give them a couple of weeks to rebed in
Cheers
jr

[DavidR]

We are all entitled to our opinions DavidR

Absolutely

But i personally would give them a couple of weeks to rebed in
Cheers
jr

Interesting...

[BW]

I have two opinions over here as similiar to the aboves issue. Since I have found the vibration after the race came from lossen front suspension brackets, and the stock wheels.
Now I have done the alignment, changed fluid yet the pads the front brakes just excellent as before.

The kits completed in November, this failure caused after the custom air ducts have been broken hoisted under my spoiler, then the brakes failed after my car stopped in the pit without fan blowed.
Of course the whole caliper turned into golden purple from bright silver. Fluid has boiled and have to replaced.

DavidP, the brakes are heavily used at my track race in December, it actually did not failed at all by very hard push against mainly 360s, GT3RS got three, kissing the tail on the tough one, definetly behind 996turbo. Due to the weight of the vehicle, the power and the brakes, setup let the car been able to go a further limited. Now we are working on a fibre designed spoiler similar to the new R36 which is allowed more space to collect air to the brakes that help the problem. I guess I will keep the current pad for street usage with a soft pad, then use a new one with more agressive pad but most important for the weight reduction and air blow duct to the brakes.

[BW]

Thanks for the comments and advises....

I have resurfaced the rotor and wonder a new pad proven a better to the disc, anyway a new disc has been prepared in case....

post new picture after my next heavy break usage.

cheers