Drilling stock rotors

[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.