A Brake Rotor Question

Dekker · Jun 29, 2014

I have the option of getting a brake adapter to fit some medium large 928S4/993 calipers to my standard 964. I can go for the larger discs as in the Big Red type 322x32 or the smaller 304x32 as fitted to a 993.
There's a big difference in the price of the discs however.

So the question is about the life of a rotor as I understand that the discs tend to crack between the drill holes.
I remember seeing ChrisW's RS had this problem.

Any advice appreciated.

clubsport · Jun 29, 2014

If you are in the Uk try to buy some brake discs. No point importing "rotors" from the US, it will likely prove too costly after delivery costs are taken into account.

As for as cracks on 322mm discs between cooling holes, this is totally down to how you drive.

On the road, you really are unlikely to cause these cracks, they are mostly from braking on track when the discs are hot and not cooled properly.

Even with cracks of 3mm they are still fine for an mot, it's only when the cracks start to join up the holes you need to be a little concerned.

On the road with standard pads you should be looking at tens of thousands of miles. On track with harder pads they may last anywhere between 5-30 track days, totally depending on your use and braking technique.

Hacki · Jun 29, 2014

All the discs crack between the drill holes. It depends on the way they are used. On track it won´t take long and the cracks will appear. As long as they are not too big (and don´t reach the outside of the disc), it´s not a problem. I doubt that the life of the bigger disc is much longer.
The choice of brake pads and the driving style (i. e. braking technique) has a way bigger influence IMHO.

For road use I don´t see a reason for the bigger disc. BTW, the cracks will appear on discs used on the road also - it´ll just take a little longer. And it doesn´t really matter.

I hope this helps,

Hacki

Dekker · Jun 29, 2014

Thanks Paul & Hacki,

I was wondering whether it was braking style or not cooling the brakes down properly on Trackdays.

At the moment I don't envisage more than 5 trackdays a year but I don't want to upgrade the brakes again at some future date, best to do it at the start. I've seen the 322mm rotors on Europarts for £270, it's one of their discount weekends so I might just take advantage of it.

Cheers, David

clubsport · Jun 29, 2014

With the discs, from experience I would tend to buy original equipment.

I have bought parts from ECP, some of the brake parts of different manufacturers may not last as long, so it could work out to be a false economy?
Make sure the ones they are selling are to manufacturers spec rather than just a replacement.

When you use the drilled discs particularly on track, you will find the cooling holes fill up with brake dust from the pads.

If you frequently use a twist drill or skewer to keep the holes clear, this helps maintain the cooling abilities and greatly reduces the chances of cracking around the cooling holes.

Yes, it is a pain, but only required between trackdays and hardly ever likely to occur with road use.

ChrisW · Jun 29, 2014

The only thing to watch is that Performance Friction discs should always be used with performance Friction pads --- so if PC discs are fitted, fitting any other pad will cause problems.

I had this problem on a 996 GT3 MkI that I purchased --- I didn't realise that it had PF discs fitted and I fitted repacement Pagid pads ... cost me discs and pads, and a track day !!

The discs went a beautiful blue colour and even skimming the discs and the pads didn't solve the problem.

Needless to say, the brakes didn't work ... until I replaced the discs and pads ...

Hacki · Jun 29, 2014

ORIGINAL: clubsport

With the discs, from experience I would tend to buy original equipment.

+1

Steve Brookes · Jun 30, 2014

David, if you go with 993 calipers, you must use the 304mm discs in 928 fitment. You can't use the 304mm 993 discs because they have the wrong offset for a 964.

Laurence Gibbs · Jun 30, 2014

I got far more years than i'm prepared to admit on here out of my disca. So long as you stay away from the super aggressive pads and cool the discs before coming in the pits you'll get plenty of life out of them.
if you haven't seen this already, it's very useful.

Dekker · Jun 30, 2014

ORIGINAL: clubsport

When you use the drilled discs particularly on track, you will find the cooling holes fill up with brake dust from the pads.

If you frequently use a twist drill or skewer to keep the holes clear, this helps maintain the cooling abilities and greatly reduces the chances of cracking around the cooling holes.

Yes, it is a pain, but only required between trackdays and hardly ever likely to occur with road use.

Thanks, good tip.

The discs on offer are OE Quality.

ORIGINAL: Steve Brookes

David, if you go with 993 calipers, you must use the 304mm discs in 928 fitment. You can't use the 304mm 993 discs because they have the wrong offset for a 964.

That would be a problem with off the shelf brake adapters, however I know Simon at Pro-9 who gets the offset corrected at the adapter. Also Bill Vertburg has written about brake upgrades extensively on Rennlist.

Dekker · Jun 30, 2014

I hadn't seen the Bill Gregary list Lawrence, thanks.
(edit:- I've just seen it's on the end of my pdf file, I'd never scrolled down that far.)

I have seen another one by Bill Vertburg.

Brake Systems

Steve Brookes · Jun 30, 2014

ORIGINAL: Dekker

That would be a problem with off the shelf brake adapters, however I know Simon at Pro-9 who gets the offset corrected at the adapter. Also Bill Vertburg has written about brake upgrades extensively on Rennlist.

No not really. The 'off the shelf' adapters allow the use of either big red calipers with 322 mm discs (993TT) or 964RS calipers with the same discs or 993 calipers with the 304 mm 928 discs. This is all in Bill's write ups. However, I would advise anyone using 'off the shelf' adapters to avoid the DesignTek ones I used because the quality was shocking - they needed helicoils even before fitting. Not good, considering that they were £200. Go for the FVD or Rennline ones instead.

Laurence Gibbs · Jun 30, 2014

I think i must have mean't Credit to Bill Verburg. Though it's so long ago now I can't remember where it came from. The trick for 64 RS owners is to use the 965 turbo front discs as they are cheaper than the 64 RS discs, only difference is the turbo disc has a bigger pad area for the big red calipers. The 64RS uses a smaller caliper and pad but can use the same disc(it just does not use the extra portion of the disc). Info also origainally from Bill i think.