Checking thst discs are within correct tolerance 993 C4S

[Jasper]

Hi,

I checked my discs with a vernier calipers on my 1997 C4S and read 29MM? I notice there is a lip
on the disc which may prevent me from measuring actual thickness ? Would a 97k mile car discs be worn at this stage ? do I need to use a Micrometer to measure same ?

[Mick Cliff]

Replacing discs seems to be more of a regular service item these days, as opposed to the 'old days'.
Lipped or worn discs can be skimmed of course, providing there's enough 'meat' on the disc.
I think Porsche give minimum thicknesses to work to
Some workshops can skim insitu

[haasad]

Hi , you do need to measure the worn area, the "lip" is approximately the original disc thickeness ( give or take) A micrometer is unlikely to have enough throat depth to allow proper measuremnet and will only give point readings ( which you could average to get a number). A vernier may have a relief at the bottom of the jaw throat to clear the lip or you should use a spacer of a known thickness each side of the disc the measure with a verier including the spacers then subtract the spacer thickness from the measured value to give your average disck thickness.

cheers

andy

[Nige]

If in doubt replace them, they generally don't cost that much especially when compared to pads. Also look out for cracks and warpage, if they're crusty and have more ridges than a packet of crinkle crisps then just swap.

At 97k I doubt they're the discs that it left the factory with, but this all depends on what previous owners braking habits are and if harder type of pads have been installed along the way.

[Jasper]

I checked the thickness on my discs with a Micrometer on 3 different points on each disc, I found the following :- 30MM Front right, 31MM Front left, 26MM Back right, 25MM Back left, I measured on the wear surface area in all cases.