That's cracked it

[Doodle]

This evening's investigation into the noise from the SL's front wheel has come up with a possible culprit - and not the one I was expecting.

From what I can determine, it's caused by what appears to be 3 full-width radial cracks on the disc catching on the brake pad. Genuine MB discs too, although they've been on a while and would have needed replacing at the next pad change (probably the next service in about 6k).

It seems I need to go looking for some discs with better heat capacity/shedding.

 

[WDB124066]

Photo...?

What pads are you using with this disc?

 

[Doodle]

Proper MB pads too. Didn't have time for a photo, was getting dark and I was hungry!

It's at PCS next week so will get Olly to confirm.

 

[WDB124066]

Be interesting to see what Olly makes of it, how common this is...??

 

[Doodle]

Probably not that common...I do tend to make the most of the performance!

 

[WDB124066]

Ah, you've got to learn that you're in a car and not on a bike, you don't need to slow down so much for corners - you need to learn how to carry more speed through the corner [on the track]...

In all seriousness I'm interested in this for obvious reasons, be good to get some feedback next week...

 

[Doodle]

Lol...I won't even answer that one!

 

[grober]

Can't go wrong with ATE [ Alfred Teves] stuff - OEM to MB.

 

[BlackC55]

Sounds interesting. I will have a look next week

 

[Doodle]

Ta muchly...then we'll find out if I'm totally wrong or not! I suspect the calipers would probably benefit from a little fettling too.

 

[Doodle]

Can't go wrong with ATE [ Alfred Teves] stuff - OEM to MB.

Unfortunately, that's what these were. ATE discs direct from Mercedes.

 

[Sp!ke]

I struggle to understand why genuine disks would crack under normal driving conditions. Could you have a sticky caliper or something?

 

[Lord-WYBMAnE220]

Cracking happens when the discs get too thin.
I'm suprised you experienced no warpage (brake grab, etc) which would normally happen long before you get to the cracking stage.
If you can feel a lip on the outside edge of a disc, it's worth checking the thickness is within tolerance.

 

[Doodle]

I struggle to understand why genuine disks would crack under normal driving conditions. Could you have a sticky caliper or something?

Everything looked fine in that respect, but I'll ask Olly to give the calipers a once over anyway.

Cracking happens when the discs get too thin.
I'm suprised you experienced no warpage (brake grab, etc) which would normally happen long before you get to the cracking stage.
If you can feel a lip on the outside edge of a disc, it's worth checking the thickness is within tolerance.

Are you talking about warping in its proper sense, or the symptoms that often get attributed to it (pad transfer, hot spots, etc)?

Either way, the only warning was the noise - brake feel and performance hasn't changed (in normal use...I'm not pushing them to find out!). They're pretty sizeable (320x30) and while they're at the end of their service life, they aren't over-worn.

 

[Lord-WYBMAnE220]

and while they're at the end of their service life, they aren't over-worn.

If they're still within thickness tolerance, then they really shouldn't be cracking.

 

[ray_hennig]

Can't go wrong with ATE [ Alfred Teves] stuff - OEM to MB.

Have to disagree there although a year ago I would have been with you all the way.

Last rear discs (ATE) I fitted 3 years ago and there was a squeak and vibration until MB ones were fitted recently. Now all's quiet.

Someone on another board said that some ATE parts are now Chinese made and quality is suffering. I have no proof of this.

Anyway, this has now led me to an MB only policy since it's a pain for me to get to garages for rework.

RayH

 

[Lord-WYBMAnE220]

Some friends mock me, but I fit dealership-supplied OEM pads because other brands (even expensive ones) leave really stubborn, brown deposits on rims.

 

[Dieselman]

Some friends mock me, but I fit dealership-supplied OEM pads because other brands (even expensive ones) leave really stubborn, brown deposits on rims.

That's because they are Sh!t...

 

[johnsco]

Brake discs (even good-quality ones) suffer a very-hard life.
They are constantly being heated-up and cooled down in a very short space of time - The heat distribution is often severe and uneven - The thinner they get, the more extreme is the thermal fatigue that they endure.
Perhaps we should be surprised that they don't crack more frequently.

Other real problem is that a very-large proportion of brake discs in use today originate in China (no matter what label they carry).
Some of them are utter rubbish.

I fitted a set of front discs to a Jeep Cherokee not too long ago.
They looked horrible when I took them out of the box.
So much so - That I ultrasonic tested and dye-pen tested them before fitting.
They were not obviously rejectable, but their surface was a variable colour - Which is not a good sign on machined castings.
I fitted them with usual care - New pads at the same time.
Twelve months (25k miles) later, the braking was lumpy.
The discs were clearly disintegrating.
I got my money back on the discs, but needed to fit a new set of pads at my expense.

 

[grober]

Have to disagree there although a year ago I would have been with you all the way.

Last rear discs (ATE) I fitted 3 years ago and there was a squeak and vibration until MB ones were fitted recently. Now all's quiet.

Someone on another board said that some ATE parts are now Chinese made and quality is suffering. I have no proof of this.

Anyway, this has now led me to an MB only policy since it's a pain for me to get to garages for rework.

RayH

Interesting to hear that. If indeed they are Chinese made I would avoid like the plague. I notice that on the ATE USA site they distinguish between the quality of parts for the European market and the USA calling the USA product "premium line " and "European market line " .

quote from their site :-

The European ATE Web Catalog shows parts for asian and european vehicles for Europe. Parts for european or asian vehicles in North America could differ.

Please use this web catalog for European hydraulics and brake drums/shoes. ATE PremiumOne™ rotors & pads are sold under different part numbers for North American applications. For ATE PremiumOne™ products please see the ATE PremiumOne™ web catalog.

THIS WEB CATALOG ALSO CONTAINS EUROPEAN BRAKE ROTORS. THESE ARE NOT PREMIUMONE ROTORS AND ARE NOT SOLD TO US OR CANADA.

GLOBALISATION ITS A BITCH!