Posted by: T-mack
So I finally got fed up and dealt with my issue. I'm running Shigura with XT levers, MT5 calipers. I decided to take my masters apart and figure out exactly causes the wander. The system is as simple as possible IMO, a rod pushes a piston that pushes the fluid so wtf could it be? I wish I took pictures but I didn't so it is what it is. The problem with Shimano brakes is that the piston gets filthy dirty when you push the shitty fluid up from the caliper during a bleed, so the Marsh gravity bleed technique is your best bet. Even after clean fluid was filling up my bleed cup, the system was still 'sticky' because the piston o-rings were so dirty. The wander is from the piston not retracting all the way fast enough so when you grab the lever again there's already fluid in the system and you're just introducing more. The second problem is the pin that the lever rotates on is press fit into the plastic 'cams' and rotates inside. My pin and plastic were worn so bad I almost threw the levers away. All I did was rotate the pin 180 degrees to take up some of the slack when I put back together. SRAM uses bearings on their higher end brakes which gets rid of this issue. So my advice is to gravity bleed always and keep your levers as clean as possible at all times so mud and gunk doesn't get in there and make the wearing issue on the pin even worse.
Also it was interesting seeing how the 'Free Stroke' screw actually works. It just pushes on a piece of plastic that pushes the piston in, pretty simple, when you unscrew it the piston comes out which is how the system should be bled. Cheers.
I agree with your description of the "pumping up" mechanism, this get worse at lower temperatures, the oil becomes more viscous and the seals probably harden slightly.
I personally haven't seen excessive wear on the lever axle bushings or axle, definitely develops some play over time though, it would be nice to have the option to replace those bushing though. You did take the Lever Axle Set Screw Out right?
It would be interesting to see an oil analysis of what's actually in the black oil, the aluminum particle theory makes sense, but the oil in the caliper is always so much worse than the in the master cylinder/hose, I always assumed that some brake dust was being pull through the seals when the pistons retract in the caliper and/or the heat from braking has some sort of effect on the additives in the oil.
Posted by: andy-eunson
Good to know. I always wondered how the pad contact adjust worked. I always turn it out until the lever stops moving then gravity bleed. Seems to work. I also will do a burp whenever the brake starts feeling like the lever is getting too close.
I’ve read somewhere some time ago that many modern brakes don’t have a lot of oil volume so when pad wear and disc wear add up the lever gets too close. Not enough oil volume to account for a lot of wear. What does the hive mind think?
I've always burped the levers several times over the life of a pad. I figured there is technically enough oil but would bet that if you pulled the levers while the bike is upside-down with the pads 75% worn, you would introduce air into the lines.
Although, maybe that doesn't actually line up with "burping". Burping does definitely improve lever feel/bite point, so either the extra oil being added into the reservoir adds weight to fill the master cylinder piston slightly more, or air is introduced to the master cylinder as the pads wear: maybe via air and oil mixing due to vibration during riding and then being pulled into the master cylinder?
I've found that there is some degree of venting/weepage in the lever from every shimano brake I've owned. I think this is through the reservoir vent, but could also be from the master cylinder seals.
I also loosen off the contact adjust screw for full bleeds, but I turn it in before closing the reservoir, otherwise, the excess fluid seems to vent out of the reservoir.
I like the Marshy bleed, but I find that covering the caliper with oil ends up being a pain to clean fully, and I often end up with slight contamination that needs to be burned out of the pads.