Hi all, After bleeding many times and taking the 999 to P&H Crawley, none of us can remove the spongy front brake. The conclusion is a new master cylinder. no replacement parts are available so has to be a new unit except, they are very expensive! Any ideas on other units being a perfect replacment ? Maybe the unit is used on other models ?
What initially caused the need to bleed the brake, did it just suddenly become spongy or was some work done on the system after which it became spongy ? Spongy brakes are due to two possible causes, either a leak letting air in to the system or air trapped in the system. I take it there are no signs of fluid leaking out of the system ? I'm not familiar with 999's & the front brake layout, but I would focus my attention around the master cylinder when looking for trapped air. Quite often the master cylinder bleed point is not at the highest point in the system, physically. By turning the steering to the full left position & with the bike on the side stand you can get air to migrate, naturally, to the highest point in the system. I would also remove the bleed nipple & either wrap some PTFE tape or apply some grease around the threads of the nipple. This prevents air being draw in past the threads when bleeding the system. If the reservoir is part of the brake lever assembly instead of remotely connected via a short length of pipe, tiny movements of the brake lever can expell trapped air close to the piston. I would then try bleeding the system again by slowly pumping the lever whilst opening & closing the bleed nipple at the correct points in the sequence. There are other methods that various people swear by, pumping the lever vigorously prior to bleeding, vacuum bleeding, pressure bleeding & pulling the lever to the handle bars & taping it there & leave it overnight. However, if you ensure the full system is positioned, physically, so that there are no points that air can get trapped in you should be able to bleed the system & achieve a good, non-spongy brake. I would also leave the bike stood overnight in the position I mentioned earlier so that any trapped air bubbles can combine into one large bubble as that should be easier to expell rather than hundreds of tiny air bubbles, which vigorous pumping can cause. Also, try removing the reservoir top so that you can see the fluid level. Take care not to splash fluid on any paintwork !! Then, carefully pull the lever a tiny amount, (& I do mean tiny amount) a few times. Quite often this will dislodge air trapped near the face of the piston. If, after all that you cannot get a good brake then maybe you'll have to think about a replacement. As suggested above, I'd consider the RCS option rather than just the OEM part.
Bleed nipples rely on a tapered end into a matching taper at the bottom of the thread. The threads play no part in directly sealing from air/fluid.
You are partialy correct. Under normal conditions when the bleed nipple is closed & tight you are correct in that the tapered face provides the seal, preventing air from entering the system & fluid from leaking. However, during bleeding operations & espically when vacuum bleeding, air will & does pass the loose threads & enters the clear bleed pipe attached to the bleed nipple, (if that is what you are using) giving the impression that air is still exiting the system. Applying grease or PTFE tape prevents this.
In my nearly 40 years of bleeding brakes or 34 years bleeding hydraulic systems at work, I have never come across this issue.
Thanks for the advice - I have pretty much-done everything so far suggested, even run the bike hoping the bubble might move - the 999 has the easiest bleeding system, usually, there is a bleed in the reservoir that everyone says it's a sinch. Not in this case though, so am at a loss. maybe the master cylinders do wear out ?
Mine wore out and started leaking, didn’t see it as it was up against the wall in the garage, completely mullered the fairings, like RickyX said I fitted a Brembo as there isn’t a seal kit available ?
Slumdog, did you find the bleed in the reservoir, I was not sure from your posting? I did mine last spring and it was spongy and commented on by the Mot tester. Opened the reservoir, topped up the fluid level to the bleed screw and levelled the bars as far as possible. Undid the bleed, gently squeezed the lever back to the bar whilst watching the bubbles come out. 10 times like that but closing the bleed screw before releasing the lever each time and the lever is firm as feck. It is feasible that the seals on the master cylinder piston have been damaged/worn where they pass over the fluid outlet in the cylinder - this is the usual reason for the clutch master failing but you can get a £30 kit for that one. 18mm Brembo piston IIRC, if you take it apart could you post up some photos as I think the parts are available but not from Ducati. Alternatively try these folks https://www.ebay.co.uk/i/2633752893...MI0M6Qm7uO6gIVWODtCh1rdACJEAQYBCABEgLzhPD_BwE
