So, 900ss front brakes with standard Brembo set up, braided lines. Fitted brand new master cylinder and now cannot get lever anywhere near firm (would make good clutch lever!). pistons are all mobile, additional bleed nipple/banjo fitting at M/C, have bled outwards from M/C and also up from calipers, have tried vacuum pump method, have suspended calipers above M/C for days on end, ditto lever held in 'pulled' position on bars. No bubbles in expelled fluid but there is surely some somewhere. I cant help thinking it must be something simple that ive missed but cant imagine what. Has anyone on here got any useful ideas? TIA Stu
Stu, It sounds like you have tried most things. I have also had frustrations in the past bleeding MCs. Have you tried a cable tie around the lever, depressing the plunger and leaving that? The idea that the bubbles rise up and out of the fluid in the MC. Using a combination of the things you have mentioned it should eventually work. If you take the lid off the MC and watch the fluid you should see it moving as the piston works, just to check that the piston itself is ok, I know its new but you never know.
Thanks D, have tried the lever cable tied to bars to no avail. The M/C is working fine, as you say, can see the piston & fluid moving. I have ruled out the M/C to a degree since I re-fitted the old one and got the same results (I have since put the brand new one back on). I can only think it is air trapped in the callipers somewhere but cant understand why I have been unable to move it with the gallons of Dot 4 that has been pushed through the system. I guess it just going to take a while.
I would put the bike on it's side stand & turn the steering to the full L/H lock. Doing that should ensure the master cylinder, in particular the two fluid bleed holes in the bottom of it, is the highest part of the system. With the steering in the neutral, (straight ahead) position you will find the actual master cylinder lies in a slightly uphill position & the banjo bolt fitting on the master cylinder is higher, (physically) than the reservoir bleed holes. This can cause air to become trapped around the banjo bolt & makes it difficult to fully expel all the air. Ideally, pressure bleeding should be the best method of expelling any air, but I find using this method above always works providing you just take your time. Also, operating the brake lever JUST A VERY SMALL AMOUNT, (do not do a full stroke), can help expel air through the bleed holes in the bottom of the reservoir.
Either of the last two posts should be fine; however, I found that it is worth cracking the hose union banjo bolt just before the reservoir, when the reservoir is in the highest position. Wrap loads of rag either side and underneath, then cable tie the lever back, but not fully. Gently crack the union, not too far so it doesn't allow fluid to squirt out; then re-tighten before releasing the lever. Also, sometimes a good idea to leave the bike alone overnight before you do it, because all the pumping and fiddling about can split up the air bubbles, so it aerates the fluid - it needs time to settle as a single bubble right at the top of the hoses. AL
I had a similar problem and it was the surface of the bleeder nipple in the M/C. I took out the bleeder and cleaned up the surfaces. It seemed to snug up easier and my lever is solid.
