Hi all. I took the monster out today and all was well at first. It was hot today but after about 90 minutes we got to the cafe stop. Probably had an hour there and for the duration the bike was in direct sunlight. Set off from the cafe and after about 2 or 3 miles maybe I went to brake for a junction and virtually nothing. I pumped the lever and seemed to get a bit of brake, sailed past my pal in front and managed to drop into the junction and turn up against the kerb. Fortunately we were turning left and no traffic. The lever was ok by the time I’d pulled over and the brakes seemed fine all the way home. It’s not as if we’d done 30 laps of Donnington to cause fade but what else could it be? Visually all looks well and nothings been touched since the Desmo service in November….
I would venture that there is air in the brake line. Probably not very much, so you haven't noticed it although the lever is probably slightly softer than it should be. The high temperatures today have caused the bubble to expand so that when you first pulled on the brakes the lever came almost to the bars. A proper bleed of the brake system should fix it.
The ambient temperature has almost certainly played a part today as Derek said, but if it should happen again, one of the first things to do (assuming you managed to avert disaster and come to a halt!) is to immediately feel each of the three calipers to check if they are excessively hot as this is all it takes to start to boil brake fluid - often the culprit is the rear (generalising) and another symptom can be little or no clearance felt at the rear master cylinder pushrod. It only takes a minute amount of "sticky piston" in a caliper to start a heatsoak chain reaction, something which can go undetected in a colder climate.
Just as an update and I’ve not bled the system yet although I have tied the lever back towards the bar and I do now seem to have a firmer lever. I will do it properly but wanted to give an update and say thanks for the advice.
