[canadmos]

Grabbed the rear brake last night and the lever went straight to the bar and then didn't return back to its normal position.

I thought, oh crap, did one of the pistons pop out? The pads had been low for some time...

Nope. Pistons in the caliper were poking out a little, so I pushed them back in and the lever didn't budge. I tried pushing some fluid in from the caliper side, but that just ended up creating too much pressure, popped the hose off the bleed nut and got fluid everywhere. Retired to the bong shed after that one..

Is the lever hosed? Should I even bother trying to fix or just buy a new one?

 

[Serial Midget]

I didn't know people still used rear brakes, mine have always been for show... knar.

 

[canadmos]

How else are you going to do skids?

 

[Westy]

Try it knaew

 

[StiHacka]

I am quite confident that your brake lever is fvcked.

 

[Olly]

Is the lever hosed? Should I even bother trying to fix or just buy a new one?

Sounds like good old Shimano lever death syndrome hasn't been sorted for the M8000 generation. Your lever is very likely b0rked. Luckily new ones are reasonably inexpensive...

 

[Nick]

Sounds like good old Shimano lever death syndrome hasn't been sorted for the M8000 generation. Your lever is very likely b0rked. Luckily Shimano's warranty is teh awesome.

FTFY

 

[profro]

I had this happen on the gen before the m8000 and had to replace the entire assembly. Shop told me that shimano recommends cleaning the piston assembly with achohol every time you replace the pads. Maybe pad dust is getting into the pistons and messying up the whole assembly??????

 

[Olly]

Maybe pad dust is getting into the pistons and messying up the whole assembly??????

As @Udi said in another thread, it's probably this...

The dirty fluid keeps coming because Shimano use a metal-on-metal interface in the master cylinder, where the piston is machined but the bore is cast. The bore wears faster being a softer material, which in turn causes localised loading on the piston which loses its anodizing. The now bare surfaces are free to oxidise, so the black stuff in the fluid is just aluminium oxide + wear particles. If you flush it out with clean fluid you'll notice it goes black again quite soon. Basically once this happens, it's time to replace the entire lever / MC assembly - Shimano brakes are disposable brakes (best power and performance while they work though!).​