Rear brake not working

[m2pete]

Just retrieved my 2000 M2 Cyclone from my friend's garage. Was stored there for 16 years, and not ridden for 9 years. I bled the front brake line and works fine. The rear brake line will not bleed. How can I tell if the issue is the master cylinder or the caliper piston to rebuild first?

 

[Kurlon]

Take the rear caliper off it's mount, free the line up as much as possible, stuff something between the pads to act as a spacer. (I use a crushed bit of copper pipe so it's a bit softer than say, a screwdriver blade.) Hold the caliper up as high as possible, and then try bleeding it.

 

[m2pete]

Thanks for the interesting reply. Can you explain a bit how your suggestion might get the fluid moving again?

 

[Kurlon]

I learned this from fighting horrible Ducati rear brake setups, when there is a noticable dip in the line you can trap an air bubble there that is big enough to absorb the whole output of a full master pump and not get dislodged. So the master pushes fluid into the void, gravity slings it back and the net volume change in the line is zero. Meanwhile no pressure in the system so your seals never get 'worked' and aren't acting optimally.

Raising the caliper up gets gravity working for you, that air bubble wants to go up, fluid wants to go down. This means when you're working the low point, the master, fluid is always trying to backfill, so less likely to suck air, more likely to self prime and purge. Meanwhile, trapped air is doing it's damndest to get to the top where conveniently there is a bleeder to let it out. Once you get the system actually building some pressure, then you can do things like cracking the banjo at the master to get the air that always gets trapped in that maze of a passage, etc.

 

[Kurlon]

If you want to speed the process up, tapping the master, line, etc while the caliper is up in the air can help move those bubbles up if they're sticking on any corners/edges/etc. A random orbital sander with no paper mounted pressed up against the master and pulsed a few times can REALLY speed things up, just make sure the cap is ON the master before trying this.

 

[Cooter]

It's full of corrosion because no one ever changes the brake fluid. Even if you manage to free up the fluid to flush, the parts are still full of corrosion.

The right way is to take apart both the caliper, master cylinder, clean replace the seals, banjo bolt switch, and replace the line.
The get-it-going way is to take apart and clean the Mc and caliper, clear the line and banjo switch, and it will probably be ok, remembering its 1/2 of your brake system, and how important is that?
The Oh-lord-take-the-wheel way is to hammer on the Mc until you get fluid out, keep bleeding until the new fluid comes out, and never ride faster than your Angel can fly.

 

[34nineteen]

The way I’ve done a lot of tricky bleeds is to use a large syringe. Remove the reservoir, and Let it hang inside of a large plastic bag (like a gallon size freezer bag) wrap it with packing tape, zip ties or whatever to keep the reservoir draining into the bag. I remove the bleed nipple, put a little bit of Teflon tape on it (carefully). Reattach the nipple, and push a bunch of brake fluid through it. That should push the air bubble out. When done remove the bleed nipple and the Teflon tape. You may need to remove a small bubble at the nipple, but that should be easy, as the trapped air bubble should be gone.

If that doesn’t work, trying hanging the system like Kurlon suggested.

If that doesn’t work, crack the banjo at the master and see if it is actually pumping fluid. If not, a rebuild is needed (it’s super easy). If the master isn’t pumping fluid, it will feel like it needs to be bled.

I’ve found that Nissin calipers usually respond well to removing the piston(s), cleaning the pistons and seals, and reinstalling… as long as they’re not leaking.

 

[m2pete]

Preparing for the worst, I will need the right wrench to loosen the banjo bolts that hold the brake lines. Strange bolt, with I think 12 points (see attached photo), and tapered. Not a torx, as those are not tapered. I tried an E16 E-socket (the only one that fits, unless there is an E15) , but it is a loose fit. Is there a special wrench for this?

 

[Cooter]

Thanks for the interesting reply. Can you explain a bit how your suggestion might get the fluid moving again?

I'm under the impression there's no fluid moving, not that he needs help bleeding it? Maybe the OP can clarify?

 

[Cooter]

Preparing for the worst, I will need the right wrench to loosen the banjo bolts that hold the brake lines. Strange bolt, with I think 12 points (see attached photo), and tapered. Not a torx, as those are not tapered. I tried an E16 E-socket (the only one that fits, unless there is an E15) , but it is a loose fit. Is there a special wrench for this?

Looks like a worn out SAE 12-point banjo bolt. Probably 1/2", could be 7/16", but you want a set of SAE tools anyway if you're going to be playing mechanic on this motorcycle.

Those real Buells were made in Wisconsin, USA. The socket in your hand is wrong.