Front Disc Bleed Update

[gazzaecowarrior]

Hi there, I posted on here a few days ago and had some good responses. Basically I can't get pressure in my front brake when I'm bleeding it. I've done everything I should do but still no pressure. I've also acted on all the advice that was given and still no joy. I thought it was a blockage before and now I'm certain. Decided to back bleed it with a shyringe. Came up with a huge amount of pressure that was so great I couldn't get any fluid into the system. I decided to disconnect the braided hose at the master cylinder and the shyringe was able to push the fluid through with no effort at all. I can only think that the problem is located within the master cylinder as once the cylinder is connected again, there is a blockage and fluid can't be pushed through. Do people agree with me ? So what should I do now ? I was thinking of stripping the master cyclinder down and getting some compressed air and blowing it all through. Maybe get some solvent type cleaner and clean it with this too. But what solvent is safe ? I haven't got a new set of seals for the cylinder and won't be able to get hold of some before the trial on sun. Will I damage the seals by taking the master cyclinder apart or will I be able to re-assemble with the old ones still in situ ? Your thoughts would be appreciated.

[b101uk]

It is most likely that the piston in the master cylinder is not returning fully, if you have checked the clearance for the lever is ok, remove the lever and the rubber dust seal and check theirs is no dried mud or a bit of grit, sand or rust behind the circlip that holds the piston in the MC which is stopping the piston returning fully

[gazzaecowarrior]

Thanks for that. That is something I havent done yet. It would be good if it is as it would mean not having to strip down the whole cylinder. Will let you know the outcome.

[copemech]

Right on that,as the master cyl piston must return fully to open the return port for fluid(and let air escape). A fine margin here, which is why slight clearance is suggested in lever adjustment, as it cuts off early in the piston travel in the bore.

[stork955]

Gday, after the above work, if it still no good, you can strip the cylinder and clean it. It is not unheard of to have some rubbish blocking the transfer port. dont use any solvents, only warm soapy water and a nylon brush (old toothbrush maybe). Blow it out with compressed air. The transfer port is the smaller of the two holes above the piston, about halfway down the cylinder. Double check it is clear. Flush the thing with hot water and dry it out with air. Lube the piston and seals with brake fluid and reassemble. Check for clearance at the end of the piston and bleed from there.

Good Luck.

Stork

[gazzaecowarrior]

Hi there. Well I got the bike to the trial and the brake worked ok. When I stripped the master cylinder down the washer behind the circlip had become concaved. I presumed this should be flat so i straightened it. I believe it was this offending part that was preventing the plunger from moving back enough. I reassembled the cylinder and I back bled the system again. Striaght away the brake felt better. I still think there are tiny bits of air in the system but I have now been shown how to get these little bubbles out by tapping the lever gently. I will do this throughout the week. Thanks for all your help. Gaz