Cracked Brake Disk

I was busy fettling the car ready for a track day next week when I noticed that the front off side disk has cracked right through the centre of one of the cross drilled holes. Its on the inside edge and although only appears from the outside to be about 1cm long, looking at the breaking face revealed the crack to actually run about 4cm!Obviously time for some new ones after 12k miles. I was thinking of going for the Geary ones with the bolt in bell housings…anyone tried these yet or have any other recommendations. I need to get them changed before next Sat morning.

SteveI have not had any problems with the disks cracking on my Exige, but it was an ongoing problem with my 911RS. I’m told the wrong brake pads are often to blame for the heat build up. Are you a track day man & if so what pads are you using?.I like the sound of the disks with bell housings I take it these are not Lotus parts, if not you could always leave them out in the rain for a few days before fitting ( I’m not sure they will look puckka without the rust)Let us know the details on these disks I think I want some.

TrevorI recently changed from standard pads to Pagid RS14s - the motorsport pads.The Geary disks have aluminium bellhousings and in the pics I have seen look like they are gold anodised…so no rust there…available from

Any links that show details on those brakes? is useless, none of the links work.Roy

RoyI think you need to be patient with te site…its still under development…but should be worth waiting for.I’ve emailed you a pic of the disks.Steve

SteveSame problem as Roy.Would you send me the same E-mail.Many thanksTrevor[This message has been edited by trevor (edited 27 January 2002).]

I’m told Geary’s discs are excellent.

do they fit with standard calipers?same size?

I think so - the Elise gang seem to use them. Incidentally, I am interested in buying these discs - any discount for an bulk purchase?

Ordered a pair for the front today so hopefully should have them mid week, fitted friday and tested at Elvington on Sat…not sure that that will be the best way to bed them in to slightly used pads…but don’t have a choice. Just count myself lucky I noticed the cracked disk before it failed in a big way…and just goes to show the benefit of giving the car a really good look over prior to any trackdays.

Steve,how much did u pay for the 2 discs?thanksNicolas

They can just be bought in pairs,�285 per pair or �550 for a full set of4. Next day delivery is �7.95.Quote from Geary “They are even better now than you have seen as I have made a few smallimprovements. they fit straight on, no mods necessary.”

Gulp, �285 for 2, damn, thats more than i paid for my 911 Turbo discs !!! [image][/image]

Yep - but when you come to replace them you only need the outer disk, which is approx �50…Cheers

Now I’ve sourced mine I thought I would have a look around and see what else is on offer!Interestingly, Wilwood say the following""Q: Why are some rotors drilled or slotted? A: Rotors are drilled to reduce rotating weight, an issue near and dear to racers searching for ways to minimize unsprung weight. Drilling diminishes a rotor’s durability and cooling capacity. Slots or grooves in rotor faces are partly a carryover from the days of asbestos pads. Asbestos and other organic pads were prone to “glazing” and the slots tended to help “scrape or de-glaze” them. Drilling and slotting rotors has become popular in street applications for their pure aesthetic value."Maybe I should have bought solid!!!

(Coming in late, sorry…)Slotted or grooved pads are supposed to help disperse any gasses that escape from the pad material due to the heat, thus keeping the pad in better contact with the disc face. This could be snake oil, but it’s what the suppliers like to say.The other thing is that there are two types of perforated discs, those that have been drilled and those that were cast with the holes already in them, which are said to be less prone to cracks. I believe Porsche are about the only manu to specify the latter type for road cars, so if you want the cross-drilled look then it might be worth taking a look at one of the “Porsche brake kits” that are being punted about in the mags.Rgs,-= mike =-PS. Can’t see that drilling the disc would reduce the unsprung weight by any appreciable degree. You’d just be better off running thinner discs and changing them more often.

quote:Can’t see that drilling the disc would reduce the unsprung weight by any appreciable degree.I thought the idea of cross-drilling was to improve cooling / muck dispersion along with ventilating and slotting, not weight saving? [image][/image]

Hi Tony,Yes that’s what I’ve always heard. It would be easy enough to do a rough estimate of weight removed by drilling an appropriate number of holes of a typical diameter I suppose. Whatever I’d bet anyone a pint it’s not more than three or four percent.-= mike =-