Drilling stock rotors

[kaanage]

Has anyone here done this? If so, what pattern did you use - Porsche or AP?

Just having some fluid fade during track sessions (pedal going soft). And no, I'm not getting bigger brakes else my 14" rims won't fit.

[Stuwey]

Wouldn't you just go for a slotted rotor, given how cheap they can be?

[seangti]

I wouldn't suggest drilling rotors. At the rate they heat up and cool down for track sessions, which is very quickly, I've heard (and seen first hand numerous people cracking the rotors. You can have standard rotors slotted as Stuwey suggests, mine are RDA rotors than have been slotted, rather than manufactured as slotted - they are different part numbers and worked out cheaper this way. Greg at GSL recommended this so I trusted his input.

Have you looked into ducting air to your rotors?

[Tim]

You would probably have more luck trying to get better airflow to the brakes.

[brad]

What brake fluid are you using & when was it last changed/flushed?

How would you drill the rotors? (I have a recollection you are a machinist or something?) I can't see any reason why you wouldn't have a go at it. All you need do is give them a good look over after every track day & look for radial cracks emanating from the drill holes.

The worst that can happen is the rotors will stuff up quicker & you can buy proper units after that.

[kaanage]

I've peened drill holes in the past with bike rotors which stopped them developing cracks when other people's did after about the same number of running hours. Very noisy (the peening), though and the rotors were solid so vented discs may crack from the inside.

Ducting would require more modding than I'm willing to do at this stage and slotting is more about preventing the dust and gas clogging the pad/rotor interface than cooling - holes do both.

Anyone here have any experience with the Black Diamond Drilled or Combi rotors?

[brad]

what brake fluid & age?

[kaanage]

Good point - stock and 2 years (3 actually, though 1 wa spent sitting in VW storage). It will be changed before the next track outing (when my rear LCA bushes gat replaced)

[mikinoz]

I believe that drilling rotors that have been heat cycled is a no no?

[kaanage]

what happens?

[flat6]

The metal becomes more brittle after heat treatment, likely they will crack

Your best bet is change your brake fluid or upgrade the disks / pads I recon.

[Stuwey]

Upgrade fliud, pads, add cooling.

The Group N Historics have to manage without drilled nor slotted rotors, and damn some of those cars are fast!

[kaanage]

OK, I'll get the fluid changed, install my QFM A1RM pads and hope the new wheels give more airflow to the rotors.
It's just that I brake so softly on the road that the pads will go green and I will need to re-bed them before each track outing.

Thanks to all.

BTW Grey cast iron (which all rotors are made of unless your have CF or ceramic) doesn't heat treat at the temps brake rotors get to so the warning against drilling used rotors is probably to do with the possibility of micro-expansion cracks forming during use and these being across the drill holes (which would mean that they would grow VERY quickly with more thermal cycling).

[brad]

Good point - stock and 2 years (3 actually, though 1 wa spent sitting in VW storage). It will be changed before the next track outing (when my rear LCA bushes gat replaced)

That's where I'd start as it's what the problem is. Drilled rotors & cooling are peripheral.

Try Motul RBF600 or Ferodo Racing 5.1. Change every 12 months (or sooner) if doing track days.

[seangti]

Bear in mind the differences between a DOT5 and Dot 5.1. You should not mix different ratings and certainly not compounds (silicone and glycol based fluids) Brake fluid - Wikipedia, the free encyclopedia and/or D.O.T. 5 Brake Fluid

I hadn't realised such a difference between DOT4 and Dot5 boiling temps. food for thought.

I've always ran a dot4 and haven't had any issues in VW, my subaru would boil occasionally on track days.