brakes not working when bike tilted ??

[skint]

I have a track bike ( year 2000 R1 ) and a trailer I use to transport it on. Today, whilst backing it off the trailer and halfway down the ramp (ie with the front of the bike pointing into the air) i noticed that the front brake lever had gone all floppy and the front brake didnt work ... once I'd moved it back a little more so that the front end wasn't pointing up as much it started working again ok. I'd assumed that the front brake system is a fully sealed pressurized system which shouldn't be effected like this -- am I correct ?? Could it be that there's some air in the system and the brakes need bleeding ??

Thanks,

skint

[feef]

there IS fluid in the reservoir ins't there? tilting the bike back could expose the feed hole in the bottom if the fluid's low.

a
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[BFG]

Agreed. You probably leaned it over so far that all the fluid uncovered the feed hole. Probably needs more in it, or, don't operate the levers when the bike is leaned so far over.

[skint]

The resevoir fluid level is fine. If its the case that leaning the bike over/back might cause air to get into the system then what about when you go up/down a very steep hill or the bike falls over ????

skint

[BFG]

For some reason I was thinking of leaning it over sideways, sorry. Front and back it would need a hell of an angle to uncover the feed hole.

There must be something else wrong. At this stage I would be planning a master-cylinder rebuild. Sudden loss of pressure is rare.

It could be that there was air in the system trapped somewhere, and different vibration of the trailer made the bubbles rise to the master cylinder - but this is a guess.

I would try and replicate the problem, paying careful attention to the circumstances. It may help diagnose the problem.

Or maybe try bleeding it and then some careful test rides.

[skint]

ok, thanks BFG. I will see if i can reproduce the problem tonight when I take the bike off the trailer again... If I can i'll bleed the system and then try again. Will let you know what the problem turns out to be.

skint

[feef]

I know someone, years ago when sarting out at DIY maintainance who topped up the brake fluid, and was adamant it was fine. problem is, they simply removed the reservoir cap and poured it in.. didn't know to remove the rubber expansion seal... they jad just filled that lol

and no.. it wasn;t me


honest



a
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[ancientd]

Do you have the standard front brake set up with a remote fluid reservoir or has it been converted to a combined Master cylinder and reservoir? If it's a remote type then check that the reservoir is mounted properly and that the connecting pipework to the master cylinder is properly clamped with no leaks. It is possible for air to get in if the connections are not sound.
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[Guest]

If you've just had the front end in the air you won't need to bleed the brakes in the conventional sense - air doesn't travel well down hill.

As said, you probably just exposed the the hole that the piston forces the fluid down. With the bike back on the level the air will migrate back to the top of the hose and be sat there waiting for the next time you squeeze the lever - then it'll bubble back into the reservoir and you'll get your brakes back