Cracked Brake Discs M5 F10

Cracked Brake Discs M5 F10

Author
Discussion

W8PMC

3,345 posts

237 months

Wednesday 26th August 2015
quotequote all
IATM said:
I have quite a lot of talk about cooling down the brakes and not sitting with the brake pedal pressed at traffic lights at a hard run but in these situations what are people doing?


So after a heard run how long are you meant to let the brakes cool and how?
What do people do if they come to a stop at lights?
Try if possible after a hard run to more coast to a stop at lights rather than pull up sharply. Avoid the handbrake at all costs with hot discs & if waiting at lights just keep the brakes applied lightly.

Patrick Bateman

12,143 posts

173 months

Wednesday 26th August 2015
quotequote all
12k miles a fair stint for discs?

W8PMC

3,345 posts

237 months

Thursday 27th August 2015
quotequote all
Patrick Bateman said:
12k miles a fair stint for discs?
For a powerful heavy car that's driven hard, yes it's certainly possible, however you would hope for closer to say 20k. Most damage/wear will be down to bad heat/cool cycling, so if driven hard & then parked up with say the handbrake on, the discs will be cooling so slowly that this will apply undue stress on them & cracks will most certainly appear.

AW10

4,422 posts

248 months

Thursday 27th August 2015
quotequote all
And I'm guessing the rear disks will take a beating if the traction control gets a lot of use? I recall a hired Mondeo some years ago in the winter - I just buried my foot in the throttle pedal and let the traction control get me up the rather long hill through the snow. At the top of the hill smoke was billowing from the front wheel wells!

Patrick Bateman

12,143 posts

173 months

Thursday 27th August 2015
quotequote all
W8PMC said:
For a powerful heavy car that's driven hard, yes it's certainly possible, however you would hope for closer to say 20k. Most damage/wear will be down to bad heat/cool cycling, so if driven hard & then parked up with say the handbrake on, the discs will be cooling so slowly that this will apply undue stress on them & cracks will most certainly appear.
I meant in terms of wear for road use only.

W8PMC

3,345 posts

237 months

Thursday 27th August 2015
quotequote all
Patrick Bateman said:
I meant in terms of wear for road use only.
The brakes can be punished with road use. Impossible to know how the O/P drives his car but I'd probably be a tad pissed off if I drove my car sedately & the discs needed replacing at 12k, but I don't drive if softly & to be honest most dealers appear to shout "replace discs" with only minimal wear so it could be some of that also.

M5ABO

6 posts

91 months

Sunday 21st August 2016
quotequote all
My F10 M5 discs are badly cracked at just 4 months and 5000 miles old. I'd put this down to their suffering over 70 laps of the Ring, but the more I look into this, the more it seems to be a broader F10 issue that I have exacerbated. They are hardly worn at all, they just don't seem to be able to handle the heat. The big question is 'does it actually matter?'. Some of my cracks are now deep enough to be felt with a finger tip, and where you can see them starting at the edge of a drill hole, they look alarmingly deep too. I've never come across a disc disintegrating on a road car, but I guess nothing is impossible....?!

foxsasha

1,416 posts

134 months

Sunday 21st August 2016
quotequote all
Surface checking is nothing to worry about. That's a web of very fine surface lines, tiny cracks. Any true crack, especially any extending to the edge or the disc, is of concern.

M5ABO

6 posts

91 months

Wednesday 24th August 2016
quotequote all
AP Racing's advice:

SAFETY AND CARE OF DISCS.
Cast iron brake discs should not normally be operated at bulk temperatures in excess of 610 C and above rotational speeds of 3000 revolutions per minute Discs must be regularly and frequently inspected for excessive heat crazing and cracking. After heavy and prolonged use some surface crazing will often be evident. if this turns into distinct surface cracks which are radiating towards the inside or outside diameter the disc should be changed. Discs with cracks emanating from mounting holes, slots, inside diameter, scallops, or outside diameter should be changed immediately.
IF IN DOUBT REPLACE.

hertfordshire1

142 posts

186 months

Friday 26th August 2016
quotequote all
Well since the ring, my breaks squeal really bad under normal driving.

Dealer said they have over heated and its best to replace them.

They work absolutely fine, just squeal.. Its a tad annoying,

Still running the original tyres - they've scrubbed well but again are fine.

It would therefore appear that the tyres have outlasted the brakes!

Welshbeef

49,633 posts

197 months

Friday 26th August 2016
quotequote all
hertfordshire1 said:
Well since the ring, my breaks squeal really bad under normal driving.

Dealer said they have over heated and its best to replace them.

They work absolutely fine, just squeal.. Its a tad annoying,

Still running the original tyres - they've scrubbed well but again are fine.

It would therefore appear that the tyres have outlasted the brakes!
Can you see rainbow colours in the disc at all?


It's possible you tempered the discs either fully or partly - as such they should be used for paper weights only.

When an idiot young driver I tempered all 4 of my discs on a early hours of the morning drive on A and B roads. My old man spotted them the next day and knew exactly what would have been required to achieve that.... Let's say it's never happened on road use since.

hertfordshire1

142 posts

186 months

Friday 26th August 2016
quotequote all
Photos of one of the front discs..




hertfordshire1

142 posts

186 months

Friday 26th August 2016
quotequote all
hertfordshire1 said:
Photos of one of the front discs..

Car has done just over 12,600 miles




Welshbeef

49,633 posts

197 months

Friday 26th August 2016
quotequote all
hertfordshire1 said:
Photos of one of the front discs..



Wow that's driving an M5 to its performance potential. smile.

Soov535

35,829 posts

270 months

Friday 26th August 2016
quotequote all
I had the same issue with front discs on my RS4.

Audi wanted £2000 a pair.


Give them a bloody good Italian Tune Up (R) and see how you get on. It might be that they are simply glazed or have pad deposits on them from if the handbrake has been applied when the discs are hot.

These cars appreciate (when up and full operating temperature) being given a bloody good thrashing every now and then. Audi also wanted to charge me £1000 for a decarbon after my wife used it for a month. In the end I just went out at 3am and found a quiet three lane road and went up through the first three gears on full throttle three or four times, then ran it in third gear at 7000rpm for two minutes and blow me it was fine. The exhaust was a bit sooty afterwards, mind hehe

A few HARD stops from 100mph one after the other should clean them nicely.



Edited by Soov535 on Friday 26th August 14:53

Soov535

35,829 posts

270 months

Friday 26th August 2016
quotequote all
hertfordshire1 said:
Photos of one of the front discs..



These are completely and utterly fine. You're being bummed.

Soov535

35,829 posts

270 months

Friday 26th August 2016
quotequote all
hertfordshire1 said:
since the ring
I'd delete this for a start.

Just drive it.


Welshbeef

49,633 posts

197 months

Friday 26th August 2016
quotequote all
Soov535 said:
hertfordshire1 said:
Photos of one of the front discs..



These are completely and utterly fine. You're being bummed.
Maybe the discs are glazed? Take them out rasp them and put back together.

RichardM5

1,733 posts

135 months

Friday 26th August 2016
quotequote all
If they have got really hot it's possible any grease used on the pads may have melted , this can then cause squeeking. Easily fixed by taking the pads out, re-greasing and putting them back.

hertfordshire1

142 posts

186 months

Friday 26th August 2016
quotequote all
cheers for suggestions.

They do quieten down after a few hard stops.

Just can't do it with the family on board!!!