I'm guessing air bubble. Rode with a friend last year and every time we went above 6000 feet he would loose his clutch. Bled the clutch and problem went away.

 

Yep, happened to me for the first time while riding the Pikes Peak HOG Chapter's 5 in 1 High Altitude Poker Run. This involved five 10k' or higher passes in one day. For me, happened on pass number 2. Once over the top of the pass I put it in a high gear and ant it cool down on the way down. After that, the rest of the passes were fine.

Three days later I took some friends over the three 10k' passes on US-550 from Ouray to Durango, aka the Million Dollar Highway. Got stuck behind the slowest RV ever, resulting in having to stay in first gear for way too long. 2nd gear would have been lugging, uphill. At one point they slow almost to a stop on a curve. I grab the clutch handle and grabbed a lot of nothing. I had to force shift until I finally managed some downhill into Silverton. I barely had enough to find neutral when we reached Silverton. Bike cooled down while we put rain gear on and it was fine the rest of the way.

Now, I am fully aware of the dot 4 requirements to replace the fluid every two years. First two years in the CO mountains I had no issues. Over the past year I had all hydraulic fluid replaced.

I just turned 97k on this '14 Limited and it was the first time I have ever experienced this, with a lot of those miles in high altitudes.

Nevertheless, I went straight to Durango HD and they bled the system. They said they did not find any air and suggested the fluid boiled as a result of the heat. It was also recommended to stage 1 the bike to reduce the heat from the cat to the transmission.

 

"I just turned 97k on this '14 Limited"

Man! I'm always impressed (maybe a little jealous, too ) by how many miles you rack up!

What's your high-mileage record on a bike before you replaced it?

Best wishes,

JP

 

DOT 4 fluid is hygroscopic, it attracts water. Water turns to steam at 212 degrees F. Hydraulic clutch and brake systems absorb heat from the leverage termination point (the clutch push rod or brake caliper). When that happens you loose some or all of the leverage from the master cylinder until the fluid cools to below 212 degrees F, then it returns to a liquid from a vapor and will once again provide leverage.

Flush the lines with fresh DOT 4 fluid every 2 years to avoid this. In wetter climates, every year.

 

This is the highest I have had on any bike. Considering I still owe over 20k on it, I suspect I will have this one forever, lol.

 

Yep, why I had mine changed on the 2 year ownership anniversary. After my last issue, I had it changed again as soon as I got home.

 

Damned impressive, regardless!

Keep ridin' & stay safe.

JP

 

If your brakes or clutch fail when hot, the most likely cause is required maintenance was not performed and the fluid is contaminated with moisture.

The best tell-tail sign of this as the malfunction only happens when hot and once let to cool a little bit, normal operation returns.

The reason for this is at very high temperatures the moisture in the fluid begins to boil and creates vapor, you end up with vapor lock, brakes and clutch will not work, once the fluid cools down, vapor goes away and normal operation resumes.

This is why almost EVERY motorcycle maker in the world requires 2 year brake fluid flushes, I assume based on this post that the clutch MAY have the same requirement but to be honest, I have no idea (as far as HD clutches) Brakes I know .. hope this helps.

Now that I read the rest of the posts here, I can see that Nomadmax hit it right on the head with his explanation, exactly.

(I actually lost my rear brake because of this issue on a Yamaha just 5 years ago because I had no idea about fluid change in a bike AND YAMAHA BURIES this information in the "Notes" section of the owners manual instead of the ACTUAL maintenance schedule., while in the smoky mountains coming down a LARGE mountain, It was one of the longest 10 minutes of my life wondering if we were going to make it to the bottom<)

 

Without a doubt. However I was more or less on on a fresh fluid replacement, as in it being done less than a year ago. It's also why many car performance enthusiasts change DOT4 out for DOT5.1 (not to be confused with DOT5), increasing the dry/wet boiling point from 446F/311F to 500F/356F.

In my case, I feel like it just got too hot due to being stuck behind that RV and in 1st gear for too dang long. Add in running super lean in high altitude with a stock bike (and a hot cat), the engine and trans were hotter than ****.
Biggest issue was no shoulder or safe place to stop and let it cool down. I am going to talk to the MOCO to find out if 5.1 is acceptable and swap to that for one, but also going to go ahead and suck it up and do a stage 1 to the bike to lower the heat.

 

I think I found the next replacement fluid:
Castrol SRF Racing Brake Fluid

Its wet/dry boiling points are very high.

"Castrol SRF Racing Brake Fluid is an ultra high performance brake fluid and popular with the highest performing teams in the world. The key to Castrol SRF brake fluid's superior performance is its silicon ester technology. Less hygroscopic then typical fluids (ie, absorbs less water), Castrol SRF also reacts chemically with the absorbed water to reduce its adverse effects creating an industry unheard of 518°F (270°C) wet boiling point! Exceeds SAE 1703, ISO 4925, JIS K2233, FMVSS No. 116 DOT3 and DOT 4 specifications."