Rear brake "issue"

[markincyberspace]

This problem has happened only twice (though twice is enough) and it's a little worrying. I suspect it's trapped air and the rear brake needs bleeding but and second opinion (or third or forth) would be good.

In short, what happened both time was we were descending in altitude pretty dramatically (lots of switchbacks etc) from a fair height. One minute the rear was working, the next nothing. After frantically pumping the lever we got a little of the braking back but not much. About 15 mins after we levelled out onto flat ground the braking returned.

The fluid levels are good and there doesn't appear to be any air bubbles in the reservoir from what I can see.

Any ideas?

[doglegdon]

Someone else had this problem, a year or so back I'm fairly sure, check in search topics "bittie", or perhaps another who has a 'slightly less alcohol damaged memory' can remember back that far.

[Jochen]

It sound like the brake fluid needs replacing. Brake fluid is hygroscopic (?) meaning it attracts water. If to much water is in the Brake fluid and the temperature is rising due to heavy braking, the water starts to boil, causing presssure loss in the brake system. After after a while not braking, the fluid and the water cools so braking is possible again.

Greetings,


Jochen

[YEN_POWELL]

It sound like the brake fluid needs replacing. Brake fluid is hygroscopic (?) meaning it attracts water. If to much water is in the Brake fluid and the temperature is rising due to heavy braking, the water starts to boil, causing presssure loss in the brake system. After after a while not braking, the fluid and the water cools so braking is possible again.

Greetings,


Jochen

Exactly. Change the fluid and the time before boiling is dramatically increased.

[russellt]

I had the same problem on a different bike , mine was caused because I was wearing motocross boots and didnt realise that I was activating the rear brake pedal as I rode causing the brake to heat up to the point were I lost all braking , it also happened when using the back brake to desend steep mountain slopes , once it cooled down it was fine.

[markincyberspace]

Gents (one and all), that all kind of makes sense, as there was a hell of a lot of braking going on in both situations.

This is such a great website.....

Thanks!!

Mark.

[matt]

Boiled water vapour for sure. When this happens try to avoid using that brake on all turns, instead 'rotate' engine braking/clutch control and front brake and then rear. I cooked the brakes on a GSX600F once, while making the tyres pretty warm at the edges, through the Peak District many years ago. Quick a shock.....