newbie front brake problem

[pauls]

hi there all had my 05 r1100s 6 mths now and still cant crack front brake problem? you can ride all day steady and front brake works a treat soon as you give it some lever comes back to bars no pressure? have so far put new pads/braided hoses and tried a second hand master cylinder all to no avail? had probably 60 bikes in my time and never had a brake like it? even went in garage the other day and no pressure but no fluid loss? any help? cheers

[tanneman]

ABS or not?

[gus]

Hi
Sounds like air in the system to me. Take lid of master cylinder. Turn bars full lock. Be careful watch the fluid. Gentley squeeze lever. You may see tiny air bubbles. Keep squeezing till no bubbles. Turn bars opposite lock. Do the same gently squeezing lever till no tiny bubbles. Put top back on reservoir. Pull lever in under pressure , put an elastic band on and leave over night. May cure your problem . They can be a right sod to bleed sometimes.
All the best
Gus

[Bikerhoss]

If there's no fluid loss, then that's it

[pauls]

sorry forgot non abs cheers,have tried bleeding and it still does same? cant quite work out why it only does it when you are going for it? but will have another go and get back to you cheers

[Bikerhoss]

Just as an after-thought, There isn't any damage to the brake lever that's causing it to intermittently 'miss' the master cylinder piston is there

[slparry]

when was the last time the fluid was changed? I assume recently with the new parts? Was it with freshly opened brake fluid or some that had sat in the garage for a while?


Sounds like it's boiling the fluid, as it ages it absorbs moisture which lowers its boiling point and can can cause the mushiness you talk off when it's used hard.

[pauls]

no have used brand new oil and have changed master cylinders that have different levers cheers, as I say have never had a brake like it? going to nurburg in june so have to sort it? cheers

[Dai wiskers]

I'm with gus on this one little bubbles in the banjo at the cylinder

[Boxered]

If you have the race setup with your new braided hoses try reverse bleeding, ie forcing the fluid up the lines from the calipers.

Steve

[Bikerhoss]

If you have the race setup with your new braided hoses try reverse bleeding, ie forcing the fluid up the lines from the calipers.

Steve

That's what I did, coupled with clamping the lever overnight, solid as a rock

[pauls]

ok going to have a go today then clamp overnight. cheers will post outcome

[Corvus]

Hi

With air trapped in the system, shouldn't the lever have excessive travel even stationary? Still, the problem of trapped air would show itself more as the required braking force increases I suppose.

This is a bit less likely but is it possible there is water in the caliper cylinders? Water turns to vapour at a lot lower temperature than brake fluid, but would perform just fine hydraulically below 100 degrees. Just as air will rise to the highest point in the system, will water sink to the lowest? Or does water dissolve generally into the fluid?

I always make sure the banjo bolt on the master cylinder is lower than the vent hole into the reservoir when filling a system, my reasoning being that air could easily be trapped in the banjo. A lot of bikes have the banjo higher with the bike vertical and handlebars straight. Putting the machine onto the side stand and turning to left lock should be enough.

If the bike has abs, servo or a linked system, this would open up other avenues I assume? Cover the obvious first is usually the soundest policy I guess.

The elastic band around the lever. Is the idea that air under pressure will displace itself into a position to rise easier? I've tried that method and also simply leaving the air a continuous route to reservoir at atmospheric pressure, with no elastic band on the lever, and that also seems to work. Air will find the high spots given a little time I guess.

[pauls]

just took m/cyl cover off but no bubbles when lever pulled in? am now doing elastic band method, could vibration be pushing pads back? although that would not explain no pressure when left in garage sometimes.

[slparry]

just took m/cyl cover off but no bubbles when lever pulled in? am now doing elastic band method, could vibration be pushing pads back? although that would not explain no pressure when left in garage sometimes.

No