Brakes query

[yan]

Recently had TT at OPC for 2yr service - no reported problems at all!

Not too long after (~200mi) have noticed a repetitive graunching type noise at lowish speeds - reminds me of wheel bearing problems but maybe tempting fate at this stage...
Thinking I could check some basics myself I have discovered (not having previously ever checked) that the inner disc face of one rear does have a band of rust concentric with, and same width as, the cross-drilled holes right in the middle of the pad contact - no noticeable snagging however. Apart from that the brake condition is pretty good I would say with hardly a hint of corrosion even on the outer edge. (I had a C4S loan during service and its brakes were positively oosing corrosion from within but nothing that didn't get burnt off on the visible face).
Feeling the disc the band is as pronounced as the run-out part so I would guess that this situation has been there for some time and not developed in 200mi alone. That the OPC did not mention the problem maybe it is nothing to be concerned about but it strikes me as questionable.

?Any thoughts appreciated (apart from "should have bought ceramics") as to whether need to have this redressed and also what could be the root cause.

Back to OPC I guess...

 

[garyw]

Only issue I had on the 2 year service was the mention of the front discs cross holes being blocked...
£120 for them to clear them or a sunday afternoon with me doing them []
Sundays are a bit busier now.....[]

garyw

 

[yan]

Here's a picture to explain original post - is there a root problem here as I would expect the pad to be in contact across the surface and at least keep such rust at bay - or is this nothing out of the ordinary?

 

[Geoff_Fields]

I would think the problem is associated with a build up of debris around the cross drillings, which then wears a groove in the pad. Then eventually the pad will not sweep that concentric circle on the disc.

 

[yan]

Thanks - all the holes are clear (and I have not had to drill them) - maybe something loose tripped in, ripped through the pad and then disintegrated.
A perceived risk of drilled brakes - even ceramics?

With all the talk about OPCs claiming brake discs need work due to corrosion is it for this sort of thing or more general corrosion within and around that is the culprit?

 

[yan]

Reckon I could have a crack at fixing this myself : disc out, skim off at local motor engineering specialist; replace pads (both sides) with OEM parts to comply with warranty I guess.

?Any restrictions on new warranty that I might need to worry about otherwise?

Any one tackled brakes on a 997TT? I have read the 996 technical details section but wondering if there are any additional surprises with the 997 variant?

 

[sawood12]

Why do anything? If it is a groove in the pad then as the pad wears the groove in the pad will pick up the ring of metal on the disk again and start wearing it at the same rate as the rest of the disc. There is no harm in this condition. Brake discs don't always wear evenly. Why spend money needlessly?

 

[yan]

Why? Preventative: the current rust is developing since no pad contact on this circle (no amount of brake drying can prevent this). If it's got this far it could be some time before the pad gets a chance to work on it, time during which corrosion continues to build and worst case scenario compromises the brakes at more cost/inconvenience. (I have had to repair discs before due to corrosion causing brake judder). If I can be convinced that there is little likelihood of this happening then I certainly would rather leave it.

 

[Rodney Naghar]

It's not uncommon, and I would be inclined to follows Scott's advice. The disk would certainly need replacing long before it would ever rust right through (never heard of this). If however you are still concerned, why not rub an abrasive pad over the area, or change the pads.

 

[okellyt]

J

If you are under the new warranty an OPC has to do everything - and I mean everything other than topping up oil/water/break fluid. If you/ quick fix it or whom ever so much as tighten a wheel nut Porsche can invalidate the warranty[]

So not even running repairs on your own car[]

 

[garyw]

ORIGINAL: okellyt

J

If you are under the new warranty an OPC has to do everything - and I mean everything other than topping up oil/water/break fluid. If you/ quick fix it or whom ever so much as tighten a wheel nut Porsche can invalidate the warranty[]

So not even running repairs on your own car[]

Excluding wear and tear of which the number One item is.... brakes..

I'd suggest just a new set of pads if your feeling that worried about it J
Otherwise as the pad wears it will contact the surface once again and you'll find a polished disc on both sides.

As pointed out earlier, possibly a stone or blocked hole has caused a wear spot on the pad which in turn had mean't the disc is not touching the pad at that point.

garyw

 

[yan]

Thanks everyone for advice.
Main concern is that the rust band is so pronounced that it would be better to skim it off rather than trust new pads to work over it. I say that since if it's been there for a while the surface can be uneven - in that respect if left it can cause a headache repair which will no doubt occur when I have no time for it - whilst this could be viewed as unlikely it is not out of the question and as I mentioned before I have experience of this (on a BMW).

On the subject of removing wheels I have taken them off to check for any obvious problems which would cause a graunching noise only prevalent when vehicle warm (reminiscent of a wheel bearing showing signs of age) to no avail. However, having tightened the nuts back properly the noise has gone! My only theory is that the nuts were not at the correct torque which in turn hold the disks on squarely - alternative insight welcome.

 

[sawood12]

ORIGINAL: J

Why? Preventative: the current rust is developing since no pad contact on this circle (no amount of brake drying can prevent this). If it's got this far it could be some time before the pad gets a chance to work on it, time during which corrosion continues to build and worst case scenario compromises the brakes at more cost/inconvenience. (I have had to repair discs before due to corrosion causing brake judder). If I can be convinced that there is little likelihood of this happening then I certainly would rather leave it.

I see your logic but the rate of rust propagation is much slower than you are assuming. I've seen brake discs that have been rusting and rotting in a breakers yards for years receive nothing more than a light skim to remove the rust layer and they are good to go again. Also the bells of the disks rust away and never get into a dangerous state. The rate of disc wear either side of the raised ring will be greater than the rate of rust propagation. But I guess if you want piece of mind then a skim and pad replacement is all that is needed.

 

[fireblade]

ORIGINAL: garyw

Only issue I had on the 2 year service was the mention of the front discs cross holes being blocked...
£120 for them to clear them or a sunday afternoon with me doing them []
Sundays are a bit busier now.....[]

garyw

Gary you probably know about this but some of the outer holes are only "dimples" I spent hours trying to clear them and somewhere in the forum there were many helpful suggestions (I didn't resort to the harsher methods like drills) I was pleasantly surprised when someone pointed out that I was wasting my time!

 

[tscaptain]

As I've done a couple of trackdays already this year my wheels have been off quite frequently to swap to the track tyres. I clean out the holes each time and I'm amazed at how much dust etc builds up in there in such a short time - especially given the amount of air blowing through there on track![8D] Just as well the inner and outer holes are aligned or we would be in trouble!