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Failed MOT - pitted rear disks!

NicD

NicD

PCGB Honorary Member
Member
Grrr, just been told, my 03 S has failed its MOT due to the rear disks being pitted. Dont know whether this refers to swept surface, I guess so but they looked fine to me.

Have ordered some new disks to fit myself as not flush at present.

John and Mark came down with their better halves early in the year to assist fitting the front disks but I can't ask this again.

So look out for pitting and corrosion, even for cars always garaged.
 
I'm shocked - they looked ok earlier this year as well...
Perhaps Ali needs to brake harder [:D]

We can always leave the "better halves" to do the job this time? [;)]
 
Just in case you didn't know Nic, when you try to remove the rear disc's just remember to let the handbrake off [;)]!!!
Also just check the inner pistons move freely in the calipers, this could be another cause for your disc's corroding.
It's always best to run you car round the block after washing your car just to dry off the brakes.
 
I will take some photos when the disks are off and post these.

Looks like I will have to pay for a full re-test also.
 
Did the car actually fail the brake test or did they fail it because the discs look corroded? Even with rusty disc's they should still powerful enough to pass.
 
i'm really dubious about this. I have heard it before. My guess would be that the brakes would easily pass the test and that it would take a long time for any pitting to rust through or reduce brake efficiency. Does anyone know more indepth detail about this?
 
It is a common problem on 996s, Boxsters and many other cars, particularly with drilled discs.

It tends to affect cars that are cleaned, garaged and left for a few days at a time. The manual specifically advises drying the brake discs after washing.

If there is enough thickness in the discs, they can be skimmed, saving a lot of money.
 
I have had cars pass the MOT with corroded discs. As long as acceptable and even braking efficiency can be demonstrated on the rollers, that should be sufficient?

Dave
 
It does sound like he his having your pants down a bit there. If the disc was chipped or had cracks then yes he should fail it. My car gets MOT'd in April which means it dosent get out all that much over winter and my discs get a rust on them. Why dont you get a wire brush in a drill and blast the rust off with them?
P.s dont forget the backs of the disc as they will see it when the car is up on ramps [;)]

Regards,

Neil Eldred
 
I was recommended to use Wurth Brake cleaner (used by OPC too) to clean up after a wash but a drive is still the best way to fully dry the system. Remember it is not only after a wash, a drive after a rainy day is also recommended...
 
I don't understand this at all - sounds like a con, frankly. Surely the only issue is that the brakes work at a minimum efficiency, or better. If you think about available disk area - then cross drilled brakes would never pass if holes in the surface were an issue, so how can some surface pitting matter?

Andrew
 
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