ian640 Posted November 22, 2008 Report Share Posted November 22, 2008 (edited) At a trial a couple of weeks ago the front brake lever on my Rev 4 suddenly went limp and it then took huge amount of 'pull' to get it to bite - the lever has to almost touch the throttle before there's enough to bite to say, lock the wheel. I've installed a master cylinder repair kit and inspected the pads - they are OK, several mm left, and there appears to be no sign of a leak from the caliper. Fluid level is OK. But the problem persists. Anyone less mechanically challenged than me have any ideas? Do I need to bleed the brake as it may have had a leak? Thanks. Edited November 22, 2008 by ian640 Quote Link to comment Share on other sites More sharing options...
big john Posted November 22, 2008 Report Share Posted November 22, 2008 Do you have your lever pointing quite far down towards the ground when you ride? Big John Quote Link to comment Share on other sites More sharing options...
stork955 Posted November 22, 2008 Report Share Posted November 22, 2008 And do you have a good lever (firm and "normal" ) sometimes? Stork Quote Link to comment Share on other sites More sharing options...
ian640 Posted November 22, 2008 Author Report Share Posted November 22, 2008 (edited) Thanks for the replies. Big John, The opposite. I normally have my levers horizontal (a la Bernie Schreiber!) but I have been experimenting with tilting them very slightly downward in an attempt to prevent fatigue. How can the angle cause a problem? Stork, Yes, the brake normally starts to bite at the slightest touch. Thinking about it it does 'go almost normal' occasionally, but nearly all the time it's like there's no pressure there...any thoughts and theories welcome... Edited November 22, 2008 by ian640 Quote Link to comment Share on other sites More sharing options...
postmanpat Posted November 22, 2008 Report Share Posted November 22, 2008 Any chance you've cooked the fluid? has the brake been dragging? Quote Link to comment Share on other sites More sharing options...
big john Posted November 22, 2008 Report Share Posted November 22, 2008 Big John,The opposite. I normally have my levers horizontal (a la Bernie Schreiber!) but I have been experimenting with tilting them very slightly downward in an attempt to prevent fatigue. How can the angle cause a problem? My youngest son rides a 4T Beta and he had his levers pointing down steeply and the same symptoms as yours occurred, I angled them up slightly and it cured the problem! Did it occur after a change of any component? the good mechanics always ask, 'what was the last thing you did before the problem occurred'! Big John Quote Link to comment Share on other sites More sharing options...
baldilocks Posted November 23, 2008 Report Share Posted November 23, 2008 Hydraulics can be awkward if you dont know what your doing It sounds like you have air in the brake system somewhere Johns point on the angle of your lever is important, the master cylinder holds fluid which is pushed into the caliper (not all of the fluid)via the brake line when you apply the brake. If the fluid level is low and the levers are at an extreme angle you will push air rather than fluid into the brake line. take the cap off and fill the master cylinder to about 3/4 of its capacity. Once you fit the membrane and lid this should ensure that whatever angle the lever is fluid will enter the system not air when you pull the lever. the second issue is the routing of the hydraulic line. to successfully bleed the system the M cyl MUST be the highest point. If your hydraulic line has a nice arc in it to clear the headlight before dropping back down to the M Cyl you wont be able to bleed the system. So I would zip tie the line to the forks somewhere to take up any slack and ensure the M cyl is the highest point, remove the adjusting bolt from the lever and just work the lever back and forward for a while . Any air in the system should bubble out, without you having to touch the bleed nipple. Quote Link to comment Share on other sites More sharing options...
ian640 Posted November 23, 2008 Author Report Share Posted November 23, 2008 Thanks to all. The brake's not been dragging, and I'm sure I don't ride quick enough between sections to cook the fluid when braking. The fluid level is high if not too much and I've tried bleeding it with the hose always lower than the master cylinder (me holding it). I'll try Baldilocks suggestion of zip-tying it down and removing the adjuster then working the lever. I hope it works as bleeding the system via the nipple is a real hassle, even with a brake bleeding kit, which was my next plan of attack. I'll report back. I did have a similar problem a few months back after the forks, wheel and brake lever were removed from the bike and carried such that the master cylinder was lower than the caliper (don't ask...) but bleeding the system cured it. The master cylinder's been higher ever since...apart from the odd crash. We'll see. Cheers. Quote Link to comment Share on other sites More sharing options...
ham2 Posted November 23, 2008 Report Share Posted November 23, 2008 I did have a similar problem a few months back after the forks, wheel and brake lever were removed from the bike Cheers. Aahh..now we're getting more clues. I don't know if the brake set up on the Beta 's are floaters but is this not an disc alignment /flex problem? Sorry for being a bit vague but the last time I had this problem it was so long ago I don't even recall which bike I had at the time...doh! Cue: someone smarter than me:......... Quote Link to comment Share on other sites More sharing options...
ian640 Posted November 23, 2008 Author Report Share Posted November 23, 2008 (edited) Hi, Tried Baldilocks idea, pumping for 20 mins or so. Also, loosened the nipple on the caliper and drew some new fluid through with the aid of a plastic tube and container. Pumped for a further 30 minutes or so (arms like popeye now) and it appears it's fixed, except I noticed that where some brake fluid rested on the split where the two halves of the caliper join together, the brake fluid appeared to move when I operated the front brake. I did up the screws holding the caliper together a little (they weren't loose, but not exactly tight). I'm hoping its fixed as there's now plenty of pressure and bite. So, thanks for all the replies, what a great community . Cheers, Ian. Edited November 23, 2008 by ian640 Quote Link to comment Share on other sites More sharing options...
zarkoff Posted November 23, 2008 Report Share Posted November 23, 2008 hi there does anybody think that having the bike upsidedown would do anything to the brakes as i flipped mine on asteep climb the other day and the bike was upside down for a few seconds and later i noticed the brake lever was a bit spongy i bled it when i got back and it seems fine know. just a thought anyway. Quote Link to comment Share on other sites More sharing options...
ian640 Posted November 23, 2008 Author Report Share Posted November 23, 2008 Hi Zarkoff, My understanding: There's always some air in the system, normally above the fluid in the master cylinder reservoir. When the master cylinder is upside down and lower than the rest of the system the air migrates upwards, i.e. into the brake line and then the caliper/slave cylinder. Turn the bike right-side up and the air then has to migrate back to the master cylinder. So in the meantime the brake is spongy and may require bleeding to regain its feel. Whether the bike being upside down for a few seconds after a crash would result in air entering the hose I don't know. but it wouldn't surprise me. Cheers, Ian. Quote Link to comment Share on other sites More sharing options...
stork955 Posted November 24, 2008 Report Share Posted November 24, 2008 Gday, I often start bleeding bike brakes by just cracking the lever slowly and gently many times, only a few millimeters. This helps prime the m/cyl and gets the process started. This may work if the bike has been upside down for a bit too and has a spongy feel afterwards. Easy, no tools and may get you sorted to continue riding for the day. Just a thought, Cheers, Stork Quote Link to comment Share on other sites More sharing options...
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