Hi chaps.

To cut a long story short, since installing these new front brake discs and front wheel-hubs I've got brake shudder. Its much more evident under heavier braking (which, with me, is pretty much allll the time), though it is very very mildly perceptible under normal braking. You can't feel it in a parking-lot.

I installed new brake-pads at the same time.

As per the instructions of the guys that installed it (Autoquip! Aaargh!), I've given it time to run-in (around 1000kms now perhaps), and its not any better - perhaps worse.

I believe a warped disc is the cause of it - am I right? Could it be anything else? I thought perhaps its the steering-rack or something, but if that were the case then I'd have had the problem before the new stuff was fitted too.
-Acolyte

Sounds like warped discs.
Then again if discs are not mated exactly flat against the hub this would cause what you say.
If you gently apply the brakes can you feel them rubbing then missing the discs?
Jack up one wheel spin the wheel and get someone to gently apply the brakes you shoudl hear if the discs are not aligning up with the pads.
Pete

I'd go with Peterg's suggestion that the discs aren't sitting squarely on the hubs. Did the garage clean the hub mating surfaces before installing the discs? One little bit of rust on the mating surface can make the disc sit out of true and cause judder.

Also worth checking that the calipers are sliding correctly and the little 'wedges' aren't damaged. You can check the pads themselves when you have a look. Make sure they aren't jammed in any way on the outer edges too, as this will cause sticking.

Oh, does the brake pedal 'pulsate' when you get brake judder? If it does and it did it right from when you had new discs and pads put on, I'd take it back to the garage that fitted them. It doesn't sound like they've done the job properly...

One thing I've had a lot of luck with is fitting the discs 90-degrees or 180-degrees from where they are now.

Basically, when fitting new discs, I hold a pencil on the caliper bracket, and with the disc bolted on, turn it carefully. You can see if it's out of true because the pencil starts and stops 'drawing'! Of course, you are supposed to use a clamped-on Dial Test Indicator (DTI) but really, the pencil is good enough to show up runout of 0.1mm or so.

If it's not running true, you remove the 12mm bolts and rotate the disc on the hub, and try again - perhaps surprisingly, this has always worked when I've needed it to. I had the exact symptoms that you have, and ever since when I've fitted new discs, I've taken a bit more care than I would have otherwise. I suspect that garages are in too much of a rush to bother...

Not a long job really though, and worth it before the disc gets worn unevenly. Also a good time to recheck pads, sliders etc. as Chas suggested.
-Alex