I went for a spirited drive early in the week with a few hard braking applications (maybe 3-4). Brakes then started to shudder on the next application. I've never had this issue before and have noticed no shudder at all previously. I know the Ralliart front rotors and callipers are bigger and less prone to warpage so I was surprised by this. I'm normally very easy on them (car is a manual too). However, today I took it for a drive and did 6-7 hard braking applications with no problems at all. The discs were also hot enough to ignite some dead leaves when I got back.

Could there be something else causing this episode of severe shuddering?

yep, play in ball joints or anywhere else in the steering and suspension setup.

Could the road have been rough?

Are they the original discs? Have they been skimmed before? They may simply have just warped over time and age, also, they might now be at there minimum thickness.

Plus you said, on the last application, it stated shaking, how hard did you brake? You could have simply activated the ABS.

No it wasn't ABS as it was light brake application when the shuddering started. Discs are original but look in good nick - very little visible wear. Pads about 60%. On another drive slight shudder after 7-8 deliberate hard brake applications so in normal driving shouldn't be a problem. I've done some reading on the subject. Apparently disc warpage is a bit of a myth. Shuddering is usually caused by unequal pad deposition on the disc or areas of microscopic changes in the disc metal???

I had a slight shudder when using the brakes, esp when using them hard. I checked the discs with a dial indicator and they were not that far out of spec. When the pads wore down I put on new rotors and pads now it is smooth as.

Apparently disc warpage is a bit of a myth. Shuddering is usually caused by unequal pad deposition on the disc or areas of microscopic changes in the disc metal???

Funny, my pads seem to deposit black sooty stuff all over the wheels instead. lol

Seriously, if you look at a used disc that is still flat (ie unwarped) and can see pitting in some areas, or colour changes over the disc, then that is causing the shudder. A skim will fix that, but it will come back as it is due to differences in the metal due to differential cooling rates during manufacture. Something to do with metal crystalline structure in the metal affecting the wear rate and co-efficient of friction over different parts of the disc.

If you plan on doing any spirited driving, or even for general safety, the 380 front brake upgrade is fantastic value for money. Probably the best bang for buck upgrade on a magna with single pot brakes. The calipers have two pots and the discs are larger. They have similar performance to Ralliart brakes (even slightly better if I'm not mistaken?) and the complete upgrade can be had for sub $500 if I'm not wrong.

Ralliarts have dual piston callipers standard

Anyone who has actually personally placed a rotor on a brake lathe will immediately disagree with anyone who states rotors warping is a myth

I have bought some DBA 4000 series T3 rotors with QFM HPX pads. Should be a nice upgrade.

I got the T3 Club Spec on mine with Bendix Pads, they are awesome, once I change the brake fluid, should be even sweeter.

Yep, I'm with Mal.

Disc warpage as well as disc thickness variation is no myth it's REAL !!!.
I've even seen some hard spots develop on discs that the brake lathe cutter jumps over. There are some shit rotors out there.

From your discription it sounds like your rotors need a light shim if the have enough material.

Cheers Dave