Just been window shopping on KAD's website and was reading that with their calipers for 7.5's to fit under 10" rims, it's possible to machine down 8.4" rotors to 7.5".

Will this work when using factory Cooper S calipers?

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It is possible to machine 8.4" discs to 7.5". It has been done to vented discs on some brake kits I've seen, so I can't imagine it would be an issue with the solid discs (they get machined to 7.9" on heaps of kits too)...

I've looked very closely lately at using machined down 8.4's with 'S' calipers. Long and short is it won't work without mods and from a cost and safety point of view it's probably not worth it. I've just ordered a 7.5" 'conversion' kit

Basically, as far as I could see, the 7.5" disc (as standard) sits much further 'in' (closer to caliper mounting flange), so you would need to machine down the caliper mounts/hubs to move the caliper into the 'right' position to sit over the cut down 8.4 (which sit further 'out'). The construction of the 8.4" disc (well the ones I have here anyway) rules out moving them in because of the mounting boss for the drive flange (guess that's why the 'S' ones are 'hollow' in the middle)... I don't think they will move far enough in without fouling on the hub and I would not turn the centre down as this is where all the metal is that the drive flange bolts to. I guess you could mod the hub but then you're going to have issues find some way to seal the bearings...

It's all a catch '22' and seemed a huge PITA so I'm just going for something I know will work and is safe.

The disc rotors when compared in price to the calipers are peanuts. Just buy the correct discs.

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You will need S drive flanges too. The 8.4s won't work.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

It looks like the KAD setup is the same as my TAROX one kev and uses the same 8.4" driveflange.

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Starlet Conversion:
http://www.ausmini.com/forums/viewtopic.php?t=15484

He's talking about using S calipers...
My reply was to GT mowog, if you use S rotors you MUST use S drive flanges- they are different. The studs are in the S rotors, not the drive flanges like yours.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Well that is true, you need to use the correct drive flanges for the job, but if your pockets are deep enough to purchase KAD Calipers then the correct 'off the shelf' discs would be only a very small cost. If Drive Flanges are also required then these too are not expensive.

<EDIT> The post I gave was in response to the original question "Is it possible to machine down 8.4 rotors to 7.5"

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