My front brake has been a problem for the last few years. Several have bled it and it works out for a bit but then seems to have air in it again.
So I figured I'd just do a rebuild and bleed. The rebuild (master cylinder) went smooth with the exception of reinstalling the dust boot. I figured out after the first time I put it in with great difficulty that the rod, spring and dust boot get assembled first then installed to the cylinder. So now my dust boot is torn in a few spots - there's some kind of tool for this other than a couple of small blade screwdrivers and shaky hands. Something called a Bush or something or other, perhaps a bushing tool?
Anyway, so I proceed to put it all back together and back bleed (fill) from the caliper bleed screw. This involves pushing fluid up the system and syphoning out the master cylinder. Did this no fewer than 10 times and the level is mush. Like.....nothing. Doesn't make sense.... It's impossible (read difficult) to install the piston wrong, the seals are preassembled on it, and if they were somehow backwards it'd spew out at the lever.
So for kicks I finally just try a regular bleed - tie the lever tight and crack the caliper bleed. Instantly the lever is solid. Why? I'm going to guess maybe the back filling leaves a air pocket somewhere - must be at the caliper end somehow. Now to the credit of the 'bleeding kit' instructions - it says to fill and then draw and fill a few times. I couldn't manage to do this without sucking air around the bleed screw. So - that's what works - Peter mentioned keeping a loop in the fill tube, perhaps this is the trick. I thoroughly tapped the fill tube to work out any air which worked well....but....whatever. Levers are feeling better than ever now. Let's hope the dust doesn't assault that ripped boot too badly in Moab.
So I figured I'd just do a rebuild and bleed. The rebuild (master cylinder) went smooth with the exception of reinstalling the dust boot. I figured out after the first time I put it in with great difficulty that the rod, spring and dust boot get assembled first then installed to the cylinder. So now my dust boot is torn in a few spots - there's some kind of tool for this other than a couple of small blade screwdrivers and shaky hands. Something called a Bush or something or other, perhaps a bushing tool?
Anyway, so I proceed to put it all back together and back bleed (fill) from the caliper bleed screw. This involves pushing fluid up the system and syphoning out the master cylinder. Did this no fewer than 10 times and the level is mush. Like.....nothing. Doesn't make sense.... It's impossible (read difficult) to install the piston wrong, the seals are preassembled on it, and if they were somehow backwards it'd spew out at the lever.
So for kicks I finally just try a regular bleed - tie the lever tight and crack the caliper bleed. Instantly the lever is solid. Why? I'm going to guess maybe the back filling leaves a air pocket somewhere - must be at the caliper end somehow. Now to the credit of the 'bleeding kit' instructions - it says to fill and then draw and fill a few times. I couldn't manage to do this without sucking air around the bleed screw. So - that's what works - Peter mentioned keeping a loop in the fill tube, perhaps this is the trick. I thoroughly tapped the fill tube to work out any air which worked well....but....whatever. Levers are feeling better than ever now. Let's hope the dust doesn't assault that ripped boot too badly in Moab.
