I’ve recently changed the pads on my Cailbre Bossnut. Brakes have been perfect from new, but it was time to change the pads.

Bike came with a shimano groupset M447 calipers.

Put on some Aztec pads on. I don’t know, but looking them up, I’d say they’re sintered. I live on a steep hill, so rode down it with the brakes on. Got to bottom and they were still dead. Rode the night, and by the end, the front was stopping, but there was a massive judder. And the rear was still dead. Even after riding down the baccup road (for anyone that knows it).

I didn’t clean my discs, hands up.

Other than that though, did I do anything wrong? I assume the stock pads were non sintered? If so, they lasted my fine, and stopped perfect from new. Should I just get some cheapie shimano non sintered ones?

You have to bed brake pads in. Basically you pedal around and pull each brake for at least 10 times so they are almost at the point of stopping. they usually settle in then. To stop them from rubbing or to centre them, undo the caliper fixing bolts then squeeze the brake lever and hold it there will you do the caliper bolts up again.

He’s already bedded the pads in.
Perhaps lightly sand the rotors with some 1200 grit paper, clean the rotors with IPA and lightly sand the new pads to get rid of any glaze. Then find a nice steep hill, get up to 20mph, brake hard to almost a standstill and repeat 4 or more times.
He shouldn’t need to re-align the caliper if it was ok before the pads were changed.
(Oh and don’t align the calipers using the pistons to centre the caliper, it rarely works properly. Far better to do it by eye with the pads out.)
You might want to check the model of your rotors, as some shimano ones aren’t to be used with Sintered pads.

Took the rear pads out and scuffed the surface up with some sand paper. I think I made the mistake of trying to bed fronts and backs in at the same time, and ended up glazing the rears.

I realigned the both front and rear callipers, and we seem to be in the land of stopping again. Not quite as good as it was with the original pads, but passable. Think I’ll experiment with some different brands.

Thanks for the responses.

Sintered aren’t quite as grippy as organic pads, so you lose a bit of power with sintered in exchange for longevity.
TBH organic in summer, sintered in winter is my usual preference.
As I said though, double check whether your rotors are designed to be used with sintered. Sintered pads can be more abrasive so some rotors dont get on with them so well.