SLX M675 brakes. Been having problems with them for a while, I’ve seen the thread about having to pump them up to stop (which I do!). But this seems different..

Just bled F&R, pushing 30ml of fluid up into the shimano cup. Front now working fine. The problem is the rear, you can pull the lever until it bites and the brake short of works. But instead of the lever getting stiffer it then travels to the lever. It doesn’t matter where you adjust the lever reach to. I’m convinced there is no air in the system, and the LBS have no idea what’s wrong.
If it’s not air, where does the fault lie, caliper or lever?

Mine had gone soft (no bleed after shorten from new)I bled them yesterday following Shimanos instructions (bleed up, bleed down, bleed caliper, bleed lever) and all seems good. Back to firm.

Use the DM for your brake from here http://si.shimano.com/#seriesList/5

Searching t’internet, looks like it might be the diaphragm in the lever that’s faulty..?

I’ve bled these types of brakes loads of time, it’s not the bleed.

Was there black stuff in the oil coming up from the lever?

Yep, it was filthy. I bled it until the system was full of fresh oil.

if the brake is not responding to bleeds then it is time for them to go back to shimano for a warranty replacement…so long as they are less than 2 years old

When bleeding these top to bottom, I found that it worked best if pulled the lever outwards as well as pulling it inwards when pumping fluid from the reservoir to caliper. This seemed to suck more fluid down. It would expose the timing port after three repeats, so the topping up was constant, but it did seem to result in a good progressive lever feel.