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I don't disagree with your views, as something is going on, not sure that it is air pressure related in a sealed system. The bike gets just as hot at lower elevations and the clutch doesn't quit working, this only seems to happen at higher elevations, so not sure heat is the real issue. A lot of bikes have the slave cylinder in really hot locations and go up these passes and don't seem to have this problem. As altitude rises, air pressure drops, this is from the National Geographic Society, not me, so not sure how that would affect a clutch cylinder. There is no doubt something is taking up the slack in the clutch system.causing it to not work.
Hopefully this gets sorted or somebody could get hurt.
Moisture absorbing into the hygroscopic fluid is causing the issue. The slave cylinder is sandwiched between a hot engine and a hotter exhaust. On the newer bikes, the catalytic converter is in even closer proximity to the clutch cylinder, so the moisture is boiling off once the fluid reaches 212°F.
It doesn't take much to reach those temps down there. Add to that the lower pressures at higher altitudes and the moisture will boil off even faster. A TINY amount of moisture makes a LARGE amount of steam, and steam compresses much more easily than hydraulic fluid.
The reason this issue isn't present in braking systems is outlined above. The heat doesn't reach critical temperatures under normal operating conditions in those systems.
ETA:
Rubber seals and gaskets are not impermeable to moisture ingress. Moisture will find it's way into any system that's not hermetically sealed to some degree, even more so if the liquid inside is compatible with that water.
been saying this forever, many here don't seem to understand what Hygroscopic means, brake fluid needs changing at regular intervals period, I'd even go as far as saying from a fresh sealed bottle, not one sitting on your shelf for 4 years. you want top performance you need to do the work. sealed or not it will absorb water over time. personally I only use Motul 660 RBF and change it every 2 years max. on my race bikes its every 6 months or every pad change or after anytime I boil the brakes.
Last edited by mikes300; Aug 30, 2022 at 10:56 AM.
Just spoke with a friend of mine who returned from Vegas. He said he ran up on a guy with a '18 ultra, who was having clutch operation problems. He said he called a local dealer who told him, if the clutch fluid hasn't been changed at the 2 year interval, that you could have problems in higher elevations. Has anyone head that, or had that problem in higher elevations? Like up in Colorado and such.,,
Absolutely. My brother and I took a run up My Washington a few weeks ago. I lost my clutch completely pulling in to the parking lot at the top. Absolutely sucked coming back down without a clutch in the pouring rain. It came back about 1/2 way home thankfully. My brother thought it was slipping on the way up and heat caused it to boil, but I don't think so. It could have boiled because of the altitude difference, but I don't think it was because anything was slipping. I flushed it a couple of times when I got home.
I believe this may have been mentioned, but always use a high quality brake fluid from a sealed container when flushing or bleeding brake and clutch systems. Once you open a container of brake fluid, it starts absorbing moisture, and the last thing you want to do is use fluid that already has some moisture in it.
If you have an opened container of brake fluid (other than DOT5) it should be properly disposed of after 6 months. I always purchase the smallest size that suites my need because it does not hold up well on the shelf after opening. So buying the bulk size bottle of brake fluid may not be the great value it appears if to be you can't use it quickly enough. Or share with other riders may be a good option too. As far as disposing of used or new brake fluid, most auto parts stores accept old brake fluid and other fluids like engine and transmission oil etc. It is fairly nasty stuff that should not be poured down the drain or gutter etc.
They are a sealed system, what I mean by that is that they don't vent to the outside, but there is always a small dead air space above the fluid and this is what causes the moisture contamination. The cooling/heating cycles create condensation inside the clutch slave or the brake piston at the wheels. In the case of brakes the levels of brake fluid drop in the master as the brake pads wear, allowing for a bigger air space. That is why these systems have to be bled periodically.
It would be interesting to know if after the clutch was bled, somebody tried the same pass a couple of times and see if the problem disappeared. Also how old the fluid was when this event happens?
They are a sealed system, what I mean by that is that they don't vent to the outside, but there is always a small dead air space above the fluid and this is what causes the moisture contamination. The cooling/heating cycles create condensation inside the clutch slave or the brake piston at the wheels. In the case of brakes the levels of brake fluid drop in the master as the brake pads wear, allowing for a bigger air space. That is why these systems have to be bled periodically.
It would be interesting to know if after the clutch was bled, somebody tried the same pass a couple of times and see if the problem disappeared. Also how old the fluid was when this event happens?
The fluid in mine came with it when I bought it. I wouldn't be surprised if it's OE 2016 although probably not. It was on my list... Yes, fluid flush fixed all my issues.
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