Let me start by saying I have successfully bled brake fluid on countless amounts of motorcycles in the past.

Today I spent about 6 hours trying to chase down what in the heck is going on with my 2010 CBR600RR. I cannot get any respectible amount of pressure built up at the front brake master cylinder(lever). I get enough pressure to push fluid out of the calipers, but that's about it. Not even enough to bite the rotors.

A few notes that may rule out some possible causes:

-I use a mitey vac to get plenty of fluids through the system
-I see the pistons are pushing out (I removed the calipers and looked, to be sure). But again, not enough to bite the discs hard whatsoever.
-I tightened the banjos/crush washers down, and can't track down any visible leaks
-I troubleshot with TWO other working master cylinders, both exemplified the same symptoms.

Any ideas as to what to try next? I DID get this bike used, and it appears the previous owner HAD removed the brake lines at some point. I know trying fresh crush washers is a good start, but these really appear decent to begin with...Stumped

 

Maybe a bad line? It might have a spot on the inside closing up on you idk?

 

Is that possible?

 

Try putting the rubber seal on the master Cylinder when u r bledding. Had the same problem on a rr i was working on

 

It happens on hydraulic line quite often

 

How is lever feel? Any way you might be able to lightly "clamp" the hose as it leaves the master? Using a small
vice grip and protect the jaws with a rag. If the master has been bled of air, you should have good lever feel and it will verify that the master is building pressure. Then move down
thru the system, lightly clamping hoses one at a time and note any changes in lever feel after any component is clamped/unclamped. Just a guess, sounds like an internally restricted (bad) hose rather than a pressure issue. Hope you get it sorted. I did this on a car once with good results. Never tried it on a bike tho.

 

So you started with the bleeder nipple at the master cylinder and got good pressure there or you weren't able to get pressure at all from there?

 

I was able to move fluid through the master's bleed nipple, but was never able to build pressure there either. I guess I should bite the bullet and order a set of stainless lines. Worst case scenario, it's still an upgrade once I do actually solve this.

 

+1. Upgrade the lines, see if it helps. It sounds like a bad line, but who knows. Plus, who doesn't want reasons to upgrade stuff right?

 

Hmm, no pressure at the master cylinder. I think I would suspect the seals on the piston inside the MC first. You should be able to build a decent amount of pressure from there. Just to be sure, I would buy a syringe if you don't have one already and force some fluid into the MC. It would suck to order new lines when you needed a new seal rebuild kit.