Been using the HT for commuting, rear pad is fairly new. I'm getting barely any braking performance off them and a really noisy squeal. About half way I've got a steep descent where I can pump it and I get the bite back again.

Stick the bike back in garage for a couple of days and I'm back to the same issue. Rotor is cleaned, not having the same problem on front with same pads.

Thought it was just some crap into the rear brake after a wet ride home, but it's happening on dry ones too.

Have I glazed it? Thought I'd bedded it in okay. Bleed doesn't seem to have done anything.

Air in the brake lines maybe?

Given you've already cleaned the rotor and bled the brake then I'd just stick a new set of pads in and bed them in again and see what happens (in case they're contaminated). Not sure what else it could be, what compound are they – might be worth trying organic ones if just for commuting (assuming current ones are sintered).

Is the lever coming back to the bar? – air in brake lines
does the lever feel Ok but no braking force? – contaminated pads. did you use a spray lube on the chain?

Yep, sintered.

Nope, not pulling lever back to the bar so I'm assuming not air in the line.

Always pretty careful with lubes and I've given rotor a good dose of disk brake cleaner (maybe that's the problem….).

Looks like I'll try another set of pads (maybe organic/resin).

Presumably there's nowt much you can do with contaminated pads? Assuming the 'stick 'em in the oven' routine doesn't do much.

Ta chaps/chapesses.

Nope, not pulling lever back to the bar

must be pads/rotor then

Scrub the rotor with hot soapy water & change the pads

Not that I'm necessarily recommending this as a DIY solution but, we had the same problem with the OH's brakes at Drumlanrig the other week. Rik Alsopp dropped out the pads and went over them with a blowtorch to burn off any contaminants.

Scary biscuits, but it seemed to work. New pads are probably cheaper and safer, mind.

Burning off the pads and sanding them can work – but also can destroy the pads – i'd give it a go

Pads are probably glazed, replace pads, clean disk & caliper with alcohol

Couple of thoughts; the groves in the caliper that the disk runs through tend to gather all kinds of crap that can transfer back on a clean disk.

The caliper could be leaking. It takes a tiny leak to affect braking performance, and on an open-system brakes you might not get any air drawn in, so the brake will feel nice and firm (I had a leaking caliper, and managed to convince myself for 6 months it was not leaking while bleeding, cleaning and replacing pads was driving me to insanity). Thoroughly degrease the inside of the caliper and the back of the pads and then watch for any signs of oil on the back of the pads as you ride it.

(Other than that, I find road salt that gets on the bike during the winter when carrying in on the back of the car causes terrible squealing; have not found anything other for that problem than sandpaper.)

My mate had weeping Shimanos and they would clean up with some fierce use but be contaminated again for the next ride. Leek was between the two caliper halves – somthing wrong with the o ring recession one/both halves.