Problems with clutch at high elevations.,,,
Road Master
Joined: Nov 2018
Posts: 922
Likes: 898
From: Upstate NY
How is it that I can run brake fluid in my car for 10 years, clutch fluid for 10 years, every other fluid for 100K+ miles, but a motorcycle will blow up into a fiery mess if not changed religiously at 24 month?
Banned
Joined: Aug 2012
Posts: 14,866
Likes: 31,162
From: Whiskey Falls, Texas
Folks on here are simply giving their real world experiences.
Hell, this summer I've ridden multiple times in both rain and snow.
2 observations. You don't sound like you wrench much on your own, and motorcycles may be more susceptible to moisture than cars. Everything is exposed on a bike.
Seasoned HDF Member
Joined: Jan 2007
Posts: 20,616
Likes: 4,440
From: anacoco, la
because your bike has a much smaller amount of brake fluid compared to your car. just for ***** and giggles, i checked the moisture content of my 2016 gmc truck the other day. it's got 130,000 miles on it, and lives outside. vs my bike which is a 2019, has 20k on it, and lives in the garage. the brake fluid on the bike gets flushed when the moisture content reads over 3%. it's been done. i check it at every service as well. the moisture content on my truck still reads at less than 1%.
Supporter
Joined: Jan 2007
Posts: 15,788
Likes: 5,625
From: along the shore of Mishigami
It's quite possible I suppose that if you have any air bubbles in you clutch line, those bubbles might expand as you go up in elevation and affecting the clutch operation. Then at lower elevations the bubbles contract and the problem goes away Think of the bends when diving only in reverse
Road Master
Joined: Nov 2018
Posts: 922
Likes: 898
From: Upstate NY
A sealed system is a sealed system is a sealed system. Car or bike. Hell, Id even venture to guess that a motorcycles systems are even tighter as they are held closed with screwed down or bolted caps, Cars are usually just plastic screw on lids.
also start checking up on automotive brake fluid change intervals most manufactures recommend every 3 years. Just because you can run 100k+ miles and 10 years on your brake fluid should you? Absolutely not. Thats borrowed time for any fluid.
Tourer
Joined: May 2011
Posts: 469
Likes: 158
From: Alberta
This is odd. Thousands of bikes out there running hydraulic clutches with DOT 4 and I've never heard of this, except on this post and with the newer HD. A few of the bikes that I've had have had hydraulic clutches and never an issue. The 2 year change interval on brake fluid in clutches and brake master cylinders/slave cylinders is a pretty common request by the manufacturers. I would think that it is a pretty safe statement " that the majority of motorcycles out there " rarely meet the 2 yr interval.
These systems are sealed and any moisture generated has to be from the heating and cooling of the fluid. The air space in the master cylinders is minimal with the majority of it being taken up by the rubber expansion piece that sits on top of the brake fluid. So what is happening at elevation is that the change in air pressure is having an affect on some component in the clutch system. If this is just happening with the hydraulic clutches and not the brakes, I would think this is a safety issue and something HD should address.
I can only assume that the clutches work normally after you come down from the higher elevations. If so it is definitely an issue.
These systems are sealed and any moisture generated has to be from the heating and cooling of the fluid. The air space in the master cylinders is minimal with the majority of it being taken up by the rubber expansion piece that sits on top of the brake fluid. So what is happening at elevation is that the change in air pressure is having an affect on some component in the clutch system. If this is just happening with the hydraulic clutches and not the brakes, I would think this is a safety issue and something HD should address.
I can only assume that the clutches work normally after you come down from the higher elevations. If so it is definitely an issue.
Seasoned HDF Member
Joined: May 2018
Posts: 5,814
Likes: 7,147
From: Las Vegas
This thread has a couple of claims that these are sealed systems. I'm not so sure of that. When I performed a fluid moisture check on my clutch reservoir a few days ago there was quite a bit of moisture in the top rubber cover gasket between it and the top cover. I can only guess this was from riding in a few rainstorms on a recent trip.
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Tourer
Joined: May 2011
Posts: 469
Likes: 158
From: Alberta
As to your moisture issue. If that rubber cover gasket is sealing properly, you shouldn't get any water on top of it. I assure you they are a sealed system, no different than any car or truck our there.
Hydraulic clutches are similar to the brakes in that there is two main components, the master cylinder itself and then in the case of clutches a slave cylinder down nearer the clutch that actual activates the lever and with respect to brakes the brake caliper that actual pushes the brake pads. In both cases it is the lower component of these systems that actually cause problems when moisture gets into them. In the case of brakes, if the fluid gets hot enough it will lock the brakes on and with the clutches they no longer work, won't move the clutch rod. That's why you have to bleed at the lower components occasionally. If you had this lock on occur when you where out riding, if you just cracked open the bleed screw at the caliper or clutch slave cylinder and released the pressure they would start working again.
I still find it really odd that these kind of issues would be cropping up in year 2022. I know HD is relatively new to the hydraulic clutch game but really.
Hydraulic clutches are similar to the brakes in that there is two main components, the master cylinder itself and then in the case of clutches a slave cylinder down nearer the clutch that actual activates the lever and with respect to brakes the brake caliper that actual pushes the brake pads. In both cases it is the lower component of these systems that actually cause problems when moisture gets into them. In the case of brakes, if the fluid gets hot enough it will lock the brakes on and with the clutches they no longer work, won't move the clutch rod. That's why you have to bleed at the lower components occasionally. If you had this lock on occur when you where out riding, if you just cracked open the bleed screw at the caliper or clutch slave cylinder and released the pressure they would start working again.
I still find it really odd that these kind of issues would be cropping up in year 2022. I know HD is relatively new to the hydraulic clutch game but really.
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.
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.
Last edited by Ultra103; Aug 22, 2022 at 08:57 AM.