Pitted Disks

Just had annual MOT - only 2000 miles since last year (must get out more often ! ) Passed fine but advisory note that all 4 disks are pitted on inside. Car is due a full service in January so I'm thinking of getting the disks sorted at the same time. My question is - is it possible to get the disks skimmed or is this a false economy, and if so what is the likely cost (through a good Indy) compared to the cost of renewing all 4 disks ? Chris

Just replaced my front discs. The inner surfaces were in a right state - and had been for some years but they were passing the MOT with no probs. If you have to replace the pads (?) after getting the discs skimmed then I would suggest that it might be worth you just replacing the four discs as you can also check/replace the inner hand brake shoes when the rear discs come off and renew the ABS sensors and brake pad shims all at the same time - which is what I did at very little extra cost. On the other hand - are you sure that you want/need to replace the discs at all? It doesn't sound too bad to me. The inner surfaces of my front discs hardly had any discernible braking surface left on them but they were flying though the MOT and the car was braking perfectly. I have three MOT certificates that say "pitted/damaged inner surfaces of front brake discs". I only ended up doing them because I keep the car in pretty much concours condition and it was just bugging me knowing that they were shot and unsightly (if you were thin enough to get down on the floor and shove your head under the front end so that you could see them!) If you're in to track days then it might be a different matter but otherwise I'd suggest considering your options. After all, if you do decide to go the whole hog and replace them all you're looking at around £500 for the parts alone - and that's not from Porsche (of course) and fitting them yourself. If she's safe and braking in a straight line, etc you should be ok for a while. If you do end up driving the car a bit more you might find that they improve over time - mine did. (Only 1,200 miles covered in the last year - which is what did the damage![ ]) Adrian.

I think you mean the wear sensors. [ ] [ ]

Sorry, yes of course! I've got ABS on the brain at the moment as my other car has an ABS problemo. Grazie molto, Ricardo!

Thanks Adrian and Richard - looks like I might go a little longer on the existing DISCS - (excuse my incompetent spelling - been hanging around computers too often recently ! ) Has anyone had recent experience of skimming discs or is this considered a waste of time and money ? Chris

I was strongly advised to change my discs for exactly the reasons you mention Chris. That was over two years ago. The garage, who did a free check on it, advised changing all discs. Rather than authorising the work to be done immediately, I had two other 'second opinions' from independent Porsche garages in the area. Both reported that although there was some sign of corrosion "...on the inner faces" - they were fine. Now, two years on... it went through it's MOT last week with no problems. Just my two pennorth... but I am pleased I didn't simply take the word of the first garage!

Recently had my "Big Reds" done by my Indy. They say that , on average, you should be able to have three lots of skimming done before complete replacement. Just had a trackday and the stoppers are their usual high quality. Cost me £200 overall. JohnC 993turbo

Mine has just passed her MOT and was told the discs are pitted. She was hardly used by the previous owner, would this be the reason? This is my daily drive so would they improve over time?

It can be quite alarming how bad the inner faces can get, especially if the car is stored outside in wet conditions, or the brakes aren't dried after washing the car. I've had two consecutive advisories on my Boxster S brakes (=996), the first one came after covering only 1800miles that year, and the latest one last week after covering 2300miles last year ! A local B road and a few very hard stops will clean them up to a degree, depending on what state they are in. I've seen some discs come off that the inner faces were covered with soemthign mkore akin to scale than surface rust - they were still performing well on the car right up to the change. Moral of the story is make sure you dry the brakes after washing (i always do), and do 10 or so hard stops in a safe location prior to your MOT !

Yes, it will be partly attributable but even so, the quality of the steel in these discs is awful, regardless of use. I'm just hoping that my new front discs stand the test of time better than their predecessors!

Apparently they can't fail pitted or ridged disc on the MOT any more unless they have worn extremely thin. The pitting is due to the metal flakes they now use in the pads.

As long as the depth of the pitting doesn't take you to below the minimum thickness of the disk you can skim as often as you like.

And if you want to know what those thicknesses are: http://www.porscheclubgbforum.com/tm.asp?m=230692

Thanks Richard - what a mine of information you are ! Thanks guys for all your comments - I'm now quite happy waiting until service is due in January and will then ask my Indy to advise. In the meantime there does not appear to be any weakness in braking - but as my Indy says - 'you're not driving it hard enough ! ' Chris

Here's a picture from a post I did a while back about my pitted discs (where DID those two years go) I personally wouldn't have my discs skimmed unless the pitting is very light. As Richard points out in the Brake Wear Limits document the minimum disc thickness after skimming is only 1.4mm less than thickness when brand new. Especially when a full kit of parts for the front (discs/pads/shims/sensors/bolts) is £245 from Marque 21