OK, so at a steep downhill I found that my rear brake is simply not cutting the mustard. I was hauling on it with all my might, yet my rear wheel was still turning. Made it a bit hairy.

They’re Deore, I think. M445 anyway.

I’m going to take it into the LBS, but is there anything specific I should tell them to do?

spongy lever – bleeding
firm lever but no bite – contaminated pads/disc.

spongy lever – bleeding
firm lever but no bite – contaminated pads/disc.

Thanks. It might be a bit of both, but probably more of the latter.
I’m happy putting new pads on, but what’s the best way of getting rid of contamination on the rotors?

Brake parts cleaner? Several well-known brands but be sure to read the safety data sheet first. Some types will attack plastics and paint

Use either isopropyl alcohol (IPA) or a bike specific brake cleaner.

Other solvents or motor brake cleaners can contain other additives that are not compatible with bike brakes, still leaving them contaminated.

Change the pads. Mine do this about once a year – because they generate so much power from small lever angles, contaminated pads feel like air in the system.

The cynic in me says that it’s a technique to sell more pads. But then the sceptic reminds me that I shouldn’t use silicone spray so enthusiastically near the bike.

a steep downhill I found that my rear brake is simply not cutting the mustard. I was hauling on it with all my might, yet my rear wheel was still turning

Fade?

Overheated pads will change their friction behaviour – sometimes it comes back after the pads cool. Sometimes it’s a permanent change.

As mentioned most automotive stores and bike shops will sell spray cans of disc brake cleaner. Give your rotor a good spraying and let it evaporate. Prob best to take the rotor off so you don’t spray anything painted and repeat a few times to make sure any contaminates has been removed. Keep that old rag you’ve got laying around in the garage away.

There are things you can try to decontaminate pads but I wouldn’t bother. Have a fresh start with some new ones.

If your lever is feeling a bit spongy it’s defiantly worth bleeding the brake to get it working its best. I’d be having a little feel around the caliper and lever to see if fluid is leaking out anywhere. You can soon feel hydraulic fluid when you get it on your hand.

My slx brakes where the same so I’ve just got some kevlar pads from superstar and they are superb. 20% off the finned pads with a code which is on their website. Ordered them Tuesday night and they were delivered Thursday morning.

Right, I’ll give it a go with new pads and a good clean of the rotors.

Thanks.