ollys Posted March 8, 2008 Report Share Posted March 8, 2008 Just been trying to re-bleed my brakes cos after a bike shop had it and replaced the pads, it started spitting out fluid all over my back wheel last time I went out until the Master Cylinder Res emptied!! Also I noticed a drip coming out from where the rubber hose joins the master cylinder res (just looked like they had pushed it on too far) So, started with brake system completely empty. Took top off resevoir. Connected my syringe to bleed nipple. Tried pushing fluid in . . . . . and nothing. Couldn't even budge the syringe Tried it with the brake pedal depressed and not depressed, no difference. Does anybody know the cause for this? Reverse bleeding seems to be the best way, but everytime I tried it with my clutch like this it failed aswell. Just couldnt push the syringe. Is it something to do with the adjustment of the master cylinder "plunger" (technical term) Does it have to be adjusted right out/in? Quote Link to comment Share on other sites More sharing options...
jse Posted March 8, 2008 Report Share Posted March 8, 2008 (edited) "So, started with brake system completely empty. Took top off resevoir. Connected my syringe to bleed nipple. Tried pushing fluid in . . . . . and nothing. Couldn't even budge the syringe Tried it with the brake pedal depressed and not depressed, no difference. Does anybody know the cause for this? Reverse bleeding seems to be the best way, but everytime I tried it with my clutch like this it failed aswell. Just couldnt push the syringe. Is it something to do with the adjustment of the master cylinder "plunger" (technical term) Does it have to be adjusted right out/in?" My experience is that when you can't get fluid to pass through the system with the bleed fitting open, it's usually caused by the master cylinder piston not returning fully back to it's stop at the circlip (rear/front brakes and clutch system). If the piston does not pull back, the bleed hole between the piston bore and the reservoir is not open and the system can't equalize. Generally it's caused by not enough slack where the lever adjustment screw meets the plunger or a sacked piston return spring in the master cylinder (there's an old mechanic's joke about "piston return springs", but they, in fact, do exist). As for air in the system, the first thing to do is to think like an air bubble. I know it sounds kinda dumb, but keep that in mind when carefully looking at the whole system from master cylinder to bleed screw on the caliper. Every system has high spots in it where an air bubble will hide, often at a fitting that can be "cracked" (opened very slightly and tightened again while the system is under pressure). As the master cylinder stroke displaces only a small volume, you might take the brake lever off and use a #2 Phillips screwdriver to push on the piston to get a full stroke. Sometimes the angle of the master cylinder or caliper traps an air bubble in a fitting or loop in the line and you'll want to take the part off to rotate it in a way to allow that bubble to pass through the line to a point where it can be bled out. General practice is to use an agricultural syringe and pressure bleed the system from the bottom-up, rather than top-down. This way you're not fighting the natural course an air bubble travels, which is always up. This will also sound "dumb", but a lot of riders, as a last resort and after pulling out most of their hair out trying to get an air bubble out of the rear brake system (bleeding the rear brake system can be problematic and it only takes a very small bubble to mess things up) will remove the fuel tank and using a tiedown strap, will hang the bike up to a strong rafter by the back tire so the bike hangs straight down. After a day, the air in the system will rise up to the highest point, which is usually the caliper, where it can be released through the bleed screw. Jon Edited March 8, 2008 by JSE Quote Link to comment Share on other sites More sharing options...
ollys Posted March 8, 2008 Report Share Posted March 8, 2008 Ta for the reply dude, thought it might be the master cylinder not being fully open. Seem to have sorted it for now . . . the brakes work, for now lol. Tomorrow will tell Quote Link to comment Share on other sites More sharing options...
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