Rear brake

[Rookie]

Just had a rather dodgy moment. Going down a nice straight at about 70 mph, and come up at a sharp corner. It's in plenty of time, so I start applying the rear brake. Only to find it's non-existant, the pedal just went straight down, no resistance. So I get on the front brake and manage to get round the corner safely. When I'm out of the corner I pull over in a car park, and have a look. The pedal isn't loose, it's in the right position, but when I press on it, it moves much further than it should. Anyone know what this is about? I had been using the rear brake a fair bit (the disc burnt my finger when I touched it) and suddenly it just wasn't there! Any ideas?

[Robby]

Its normal for brakes to be hot enough to burn you after use.

You may have boiled the brake fluid, particularly if its old. Make sure theres some meat left on the pad and disc, then do a fluid change.

Of course, its also worth checking that there is brake fluid in the resevoir, and that there isn't now a puddle of it under the rear brake master cyl or caliper.

[Davo]

As robby said, check there is brake fluid in the resevoir. I seem to remember helping 18aprilia out, when he was complaining of no rear brake and it turned out there was no fluid in there.

Other thing to find out is if the pads & disk is new? As they'll have bugger all effect until they are bedded in properly.

Just out of interest if you were on a straight, why use the rear brake? The front brake is much better at slowing you down, I only usually use the rear brake to make minor adjustments to my speed (or when I go too hot into a corner).

[Rookie]

That is something I was contemplating afterwards. Call it habit, I tend to use rear brake and then apply the front brake a second later, if I need it. Thanks for the suggestions, I'll check the fluid. The pads and disc are not new, by the looks of them.

[stinkwheel]

Could be the brake was binding slightly, causing the whole lot to overheat. I had this on my GPZ at the weekend, the disc was a bit rusty and had been rubbing on the pads. Went to pull on the brake and "Hmm, not much there".

Pulled in and there was smoke pishing off the calliper and the disc was hot enough to burn my finger through my glove. In short, the fluid was boiling in the calliper, gas is compressable and hydraulics don't work with gas in them. Left it to cool down and it was fine.

Another couple of possabilities:

If you hadn't used it for a bit or had gone down a bumpy bit of road, the piston could have rattled back into the calliper a bit. This wopuld mean it takes a couple oif 'pumps' on the lever to bring the pads back against the disc.

I have had a bike spit one of the pads out before.

Plus what everyone else said. Have a look at the pads to make sure there is plenty of meat on them, check there is fluid in the reservoir, make sure the pads move when you press the lever (pump it up and down a few times if there seems to be no pressure). If it all seems to be working, take the bike for a short ride without using the back brake then stop and see if the disc is hot (if it is, your pads are binding).

If the piston doesn't seem to be moving, I would probably try bleeding them through with some fresh brake fluid. Obviously, if the pads are worn/missing get new ones.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Rookie]

That's brilliant Stink, I'll try all that and see if I can get to the bottom of it.