Confused about 993T calipers

[GandalfS6]

I bought my S2 with Porsche 993 Turbo calipers. I recently had to order brake pads and according to the drawings on EBC'c site, the pads are 993 Turbo.

Now as far as I know the 993 Turbo disks are 32 mm but will work with A8 314x30 disks (www.bira.org). I was on the track yesterday, and the left front disk started to crack quite badly. So tonight I measured up the disk to get it replaced (It has a disk hat that the disk bolts onto). It looks like it is a 312x25 (I am sure about the 25 but it is quite difficult to measure the diameter with the disk on the car) which is a S3/TT size.

Surely if the caliper is meant for a 32 mm disk a 25mm disk won't work? Can anybody please shed some light on this. Are the cracks as a result of the wrong disk?

[Rob W]

I would'nt have thought it would cause your disc to crack. I dont know that much about calipers but i wouldve thought the pistons might come out or leak badly????

[GandalfS6]

What I can see is that the pads on the left side has worn more on the rear side than the front, so much so that it looks as if the pad's steel backing plate at the back of the pad is scraping on the disk. This might have caused the cracks. Is the uneven wear as a result of the thinner disk? I need to quickly figure this one out as I can't drive the car like this!

[Corey]

There will be a part number on the caliper, it is a 9 digit number, hopefully it won't start with 986.
If you have 25mm discs, you could potentially have Boxster calipers as these do use a 25mm disc.

[GandalfS6]

Corey - checked and it is a 993 Turbo caliper!

[Stick Insect]

Sorry Gandalf,

the crack is a thermal crack due to overheating or similar. I have just had the same thing happen to my Mondeo front disk. It can be down to a manufacturing fault or just over work. It is very unlikely that you can return it under guarentee.

This can be a split down the disk ( as in my case ) or smaller local blistering style cracks.

HTH.

David

[GandalfS6]

Stick Insect - you were spot on! I took the disks out - attached a pic of worst of the 3 cracks. The problem was not only that they used a 25mm disk when it should have been 32mm, but they had put the disks the wrong way around! It is really nice to have ventilated disks but then you must make sure that the disks are fitted the right way around!

I have decided to try and get something like 322x32 disks to replace these. I will get some 17" wheels this week to be able to do that. The disk hat used is a 12 hole with a PCD of 7" (177.8mm). Does anybody know which disk manufacturer makes disks for such a hat?

[Stick Insect]

Hi Gandalf,

The Audi S8 disk is 323x30mm, I seem to recall in another thread about an audi disk which was 32mm thick. I don't know how the offset compares.

If the pistons are a long way out the brakes will not be as firm and you could get pad chatter and juddering.

I read on another web site that you should only re-use hats once i.e. 2 disks / 1 hat.

The crack looks similar to mine

Must get it sorted.....

I don't know about 2 piece disks. Some Porsche disks are 2 piece.

The vented disks were the other way round cos' the previous owner used to reverse fast!

David

[GandalfS6]

I prefer to go fast forward!

I had a look at all the standard Audi disks and the A8 323 x 30 is the closest to what I need. The only problem is that my disks (with 25 mm disk thickness) has a overall height of 65mm wheres the A8 disk is 59.5mm. It would perhaps be better to have the caliper bracket engineered to handle such a disk if I cant find the right disk for this hat easily. The bracket would need to be moved inwards by 8.2 mm and higher by 4.5mm but I am sure a good engineering shop would be able to do that. I must just make sure that the caliper won't touch the inside of the wheel if I move it 8.2mm.

[Stick Insect]

Gandalf

The much cheaper disk is the 314 x 30 mm disk which I have , just fits inside a 16" wheel. use spacer washers to check the 4.5mm is ok.

David