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Brake Disc Corrosion

Sparkchap

New member
Joined
15 Nov 2008
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16
Can anyone shed some light on why the inside of discs partially corrode whereas the outsides dont? I had the fronts changed a few years ago for the same reason. A recent MOT advisory picked the rear up. The pads are unsurprisingly chewed up on the leading edge. Car is a 997.1 TIA
 

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I'd say at some point the car has stood still for relatively long periods , second car etc. washed a lot and then not dried the brakes off before putting it away. Water can just sit there between the pad and the disc. There's just less air getting there to dry them off and hence inside corrodes more. Pretty common issue.

Those look totally shot btw,

Ideally after washing the car take it for a short drive to dry discs off if it's going to sit a while
 
We have had this discussion in the recent past, and if I could remember where I would have provided the link...Duh..!

My contribution was along the lines of thinking that the splash guard behind the disc may play a part in creating the corrosion, as to why that might be I have no idea.. The front discs on my 991 have a rim of corrosion circa 10mm wide that runs round the outer edge on the face of the inside of the disk, the brake pad only sweeps 5mm of that.. Just as your description, the outer face of my disks is clean and free of corrosion.

I also have an old sports car which I have owned for 20 years and it too has discs but with no splash guard, the discs are original and in my climate they do in time attract very mild surface corrosion when laid-up, this surface rust is no big deal and comes off after a rub with emery paper to reveal a smooth shiny surface, so nothing like the corrosion in your pic. Both sides of each disk are in the same good condition, and that is why I suspect that the splash guard may play a part in creating the corrosion issue issue.. :?:

Replacement discs seem to be the only option when they get to the stage that your discs seem to be at.. :?:
 
oh! and do get new pads too. I once had a new Volvo XC90 (with a proper 6 cyl engine ie not diesel) and the discs were badly corroded after just a few months. Volvo agreed but the numpties at local dealer fitted new discs but used the original pads so the new discs were buggered after a few hundred miles. You can use new pads on old discs but never never ever use old pads on new discs
 

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