Clutch question

[bob795]

Hi guys,

Last night on the way home from the office I got caught in the worst traffic jam I've ever been. It usually takes me about 30 minutes of ride to cover the 12-15 km commute, last night it took almost an hour and a half. It's just horrible. 

Anyway, about 5 km from home, I noticed that the temperature indicator showed 5 bars or max, which never happened before. Then a couple of minutes later, still in this damn trraffic jam, I noticed that I had to pull the clutch lever fully to disengage.

Then shortly after that, I kind of lost the clutch. I couldn't feather the clutch and couldn't disengage by pulling the clutch lever. The lever felt like it was just dangling here, there's no "resistance" when pulling the clutch lever. Then the bike jerked and stalled. I couldn't give it a gas cause I was in the middle of a bumper to bumper traffic jam. I put the bike to neutral, tried to start it, it started right away but still no clutch.

I then pushed my bike and filter through the traffic, trying to get away from the traffic. I managed to push my bike to the side of the road ... and I thought that the bike was over heat and that cause it to lose the clutch, so the only thing I could do was to let it cool down.

I turned the ignition off and sat there waiting. After about 5 minute, I pull the clutch and could feel that it's coming back, I could feel the "resistance" when pulling the lever... you know like when you bleed a brake, you can feel when the brake start to work again.

A minute later the clutch fully work again. I turned the ign key and saw the the temp bar had drop to just 3 bars. I started the bike and continue my ride home with no more problem.

This morning, I commute on the bike and there's no problem. It ran great as usual.

My questions: Did I do any damage to the bike or its transmission? Do I have to change the transmission oil immediately, as in now?

Thanks in advance,
Bob

[Dirty Duc]

It is probably time to change the brake fluid.  It seems likely that it has a bit of water that boiled in the heat and put temporary bubbles in your line.

[bob795]

Thanks Dirty Duc.
So, the the clutch that didn't work was caused by by air bubbles in the fluid? Is it easy to do, changing the hydraulic fluid?

[Dirty Duc]

Is relatively easy.  You need a tool that is pretty easy to build if it isn't available at your auto parts store. 

Basically it is just bleeding, but keep doing it till the fluid coming out the slave is nearly the same color as the fluid you keep pouring in the master (I've never gotten them to be exactly the same color).

Brake fluid absorbs water over time, so when it is all dark it has a bunch of water in it.  I seem to recall you live in a humid place, so...

[Howie]

Also use DOT 4 or 5.1, after your experience, 5.1 if you can find it.  Change annually.

Found 5.1    http://en.indotrading.com/product/p29940.aspx

[bob795]

Howie, thanks for the link.

So, just to be clear. What I must do is basically change the whole hydraulic clutch fluid, which is actually brake fluid, with a new one.
Thanks again guys.

[Howie]

Yes.  Since it was overheated it is a good idea.

[Slide Panda]

Howie, thanks for the link.

So, just to be clear. What I must do is basically change the whole hydraulic clutch fluid, which is actually brake fluid, with a new one.
Thanks again guys.

Simply go through the bleeding procedure. You just do it enough that you've bled off and replaced with new at the reservoir, a sufficient  volume of fluid that you can be sure it's all new.

Or, theres ATE Super Blue Racing Fluid. It's a high quality DOT 4 fluid that's, well blue. They have the same formulation, just without the blue dye as well. Having some of both makes it very easy to tell when one has fully flushed a system just by alternating the fluid colors. Flushed it with yellow/gold last time? Use blue this time and keep bleeding until blue comes out of the caliper or slave.

And just to give you more insight as to your issue. You had two things that conspired against you. 1) A little bit of air in the line 2) Water in the fluid  under those circumstances, and with enough heat the 'wet' break fluid will start to boil, creating vapor. The vapor is very compressible. So after a point no amount of lever pulling will generate sufficient force on the slave piston face to displace it, and disengage the clutch. After that point, all you're doing is compressing those vapor bubbles. So that's why, when it cools normal (ish) operation returns.

The same effect can happen in brakes. It's less common, as the brakes don't have to deal with the constant heat of the engine. But if you're pushing really hard, and doing a lot of hard braking one can boil fluid and reduce or loose brake function.... So, flush those brakes too!

[bob795]

Thank you Slide Panda for the explanation 

[Slide Panda]

No problem!

[1.21GW]

Just an FYI - if you're deciding between DOT 4 and DOT 5.1 as suggested above, and think to yourself: "heck, i should meet in the middle and get DOT 5", you'd be wrong.  DOT 5 is different stuff (silicone-based) and should not be used if your bike requires DOT 4 or 5.1.