Just a heads up.. no doubt already been mentioned. I am having to bleed my rear brake after every hard ride.
Seems the exhaust is perhaps heating it and causing boiling or something like that. Just check it before you leave guys.
I've the same problem, i traced it to a kink in the fluid hose just before the master, its just behind the lower fairing panel right hand side, I've now taken delivery of a new 800 and the factory seems to have eased the radius of the supply hose
sounds like unit to unit variances. My 14' model have fully functional rear Nissin F4 specific 4 piston brake. I thought it had more travel than my Duc's Brembo rear, but that is the way its designed as I found out from Donsy. It works great, just a different initial travel feel, but once that is taken up, it grabs like no tomorrow. Running Motul RBF600 in the system and adjusted the pedal position, now always at the ready for use comfortably. Also with ABS, its a great combo. I understand the talk about heat, but the reality is the rear brake on my Duc get hotter than heck as well as all those components are near exhaust and bolted to nearby components, including the engine block. After riding, I cannot put my hand on the Duc's rear master cylinder. I think if it doesn't work, its more related to moisture in fluid air bubbles, or defective seals.
The method for a good bleeding is the remove the caliper from the hub (also remove the hose guard on the rear arm to facilitate the job) and up to favorise natural bubble travel (it remains always bubble in the hose attached to the bike).Put a hard piece between the pads and bleed as usual.
After that job , I have a firm lever used most of the time at red lights .
Mine has stayed working after using heat shielding around the reservoir and brake line. It's sits far too close to the pipes, some peeps have moved it higher up, MV is not the only manufacturer to have made this blunder.
I have a 2007 F41000R and today after a 30min ride in 100F weather the rear brake was not working. After cooling down it came back to working condition. The problem is definitely overheating due to the proximity of the exhaust to the master cylinder. My first shot at a fix will be to wrap the aluminum heat shield with heat reflective adhesive tape. If this will not fix it I am going to try swapping out the brake fluid to a higher heat resistant one. I'll send another post if the heat tape works.
It's been done by many others mate, you might add some wrap to your exhaust in the same area. And since you've cooked the whole lot, drain and re-bleed the whole system. Remove your caliper, split it and pull the pistons, clean the whole lot and you'd be smiling long time ��
Have the same problem with my 2013 F3 800. Rear brake spongy from day one and after 3000kms brake non existent. Took it back to the dealer today and they tried to bleed it but couldn't get any pressure out of the master cylinder. Waiting for a replacement under warranty
2014 F4 with 1000 miles and no rear brake. One day is working fine, next there is nothing. This thread was a good read but I'll leave it to the dealer to figure it out since I'll be taking the bike soon to get a replacement gas tank due to bulging…. Bike is beautiful… truly Motorcycle Art… but it is turning into a headache. Didn't expect to have these issues in less than a year of ownership.
Re-bled my rear brake today after 5 months since last bleed. Definitely had air or moisture in the lines after riding for 350 miles, mix of city and freeway. It feels good again after the bleed. So, in one year, I bled my rear brakes 3 times. Using Motul RBF 600. Funny the manual says brakes need bleeding every year or two, but not multiple times a year.
i changed the rota on mine and the brakes improves 75% but i also found the ay the brake peddle is designed that my right boot used to touch it , put slight pressure on the rear pad . this then ended up heating/ boiling the fluid which meant constant bleeding , now that i worked this out and i dont do it i can easily lock the rear up to easily in fact