My rear brake ( xt’s ) which has been faultless has stopped working great, narrowed it down to the actual disc itself. When it’s wet its works perfectly but when it’s dry i can squeeze the life out of the lever and there is lots of squealing but hardly any stopping power. Tried the pads from the front which just do exactly the same so hence I know it’s something with the disc itself.
I’ve tried cleaning the disc brake cleaner, stripped it all down, cleaned and put back together but still utter rubbish in the dry!
Anyone any ideas before I buy a new disc?

Sounds like you’ve made up your mind, get on and order a new disc.

Gonna try boiling soapy water and see if that helps get rid of whatever is on it

Check the disc width, should be above 1.5mm. I’ve always found discs to start playing up when they are worn, usually the pads only pressing on certain bits due to ridges. If it’s not too worn try sanding the braking surface to roughen it up and re-bed the pads in.

This is the classic ‘Shimano seeping calliper seal syndrome’. You need new callipers, forget new pads/discs. Although your discs need thoroughly cleaned before fitting new callipers(which come with new pads)

I had the same, but on the front.

As above, short term fix is new pads and clean the disc with disc brake cleaner.

Long term fix is send back the brakes (crc in my case who have been very good) . They have a two year warranty and appears to be a known fault.

Same as above. Had problem on a front deore calliper . By the end of a ride they would be fine. Leave it overnight and no grip on the discs. Had it exchanged under warranty. It does appear to be a (well) known problem.

Any problems known with dodgy SLX finned pads?

I had a rattle from the front which I thought was the forks but have found to be the pads rattling in the caliper. Changed to new SS Kevlar pads and new spring and all is quiet again.

Why would they work perfectly when I wet the pad or disc if it was a leaking seal on the caliper?

Disc brake cleaner is crap, clean/re-face the disc with hot soapy water and some wet and dry, then re-bed them in.

Cheers Dirtydog, will give it a go!!