| Author | Message | ||
     Mmcn49 |
I go down a very steep hill on my way to work. Part way down I applied the front break. Nothing happened. The handle pulled all the way to the throttle grip with zero resistance. Pumping the handle back and forth did nothing. I had used the front break less than a quarter mile before the hill and it worked fine. After making it down the hill on fairly level road I applied the break again. It worked but the handle went a little farther in than usual. After two more pumps it was working normally, like nothing happened. Took the cover off the reservoir and verified that it was full. There were no leaks on the reservoir, caliper or brake line. The front wheel was dry, no break fluid residue anywhere. The break handle mechanical assembly and piston all look good, nothing is broken or leaking. Where should I look first? | ||
| Sloppy |
You may have air in your brake fluid or your master cylinder sealing cup isn't sealing. Bleed your brakes and see if there's any air. Do an internet search for procedure. If you have air in the brakes then I'd suspect a loose banjo bolt or bleeder line. If you continue to have problems developing pressure then you may need to rebuild your master cylinder or get a new one if the bore is scratched / corroded. Not sure of your skill level or tools though. If you're not confident then take the master cylinder to a mechanic to do it for you. | ||
| Indy_bueller |
Is there anything else abnormal with the brake? Does it shake or act like it has a "sticky spot" when you are applying it? How about the brake line, any worn spots, particularly where it might contact the fork? | ||
| Mmcn49 |
>>>Is there anything else abnormal with the brake? No. Believe me I have thoroughly looked at everything. >>>Does it shake or act like it has a "sticky spot" when you are applying it? No. It worked fine both before and after. >>>How about the brake line, any worn spots, particularly where it might contact the fork? Double checked that. No wear, no fluid. When it failed the handle had zero resistance. It was like something had broke with the handle. If the piston cup had worn or if there was air in the line or piston you would feel a spongy feeling when pulling the handle. I felt nothing like that. As nothing is obvious I’m kind of at a loss. Because of the way it failed and the lack of any fluid weeps or leaks, I’m guessing it’s a mechanical problem at the lever/reservoir. I put the longer Uly brake line on last winter, but that was 4000 miles ago. | ||
| Mmcn49 |
Additionally; I applied heavy pressure on the handle for 60 seconds without any “bleed down”. This would indicate that the seals are ok and that there isn't any air in the system. | ||
| Sloppy |
It could be many things so go start finding out what it is or isn't. It's too simple to check for an air leak to not start there. Could be a bad master cylinder but you'd feel pretty foolish if you find out you had a small leak on banjo bolt that you never saw rather than tearing apart your mc. Unless you like to work more than you like to ride... Less talk, more work!  | ||
| Gunut75 |
I would also look at the linkage in the handle at the adjustment wheel, where the lever pushes the plunger on the master cylinder. Did the lever still have a spring action to return forward, or did it just go floppy? | ||
| Mmcn49 |
Stuck in the office till this afternoon. Work starts this evening. | ||
| Kalali |
Consider yourself lucky, specially since the rear brake is generally useless. If it were my bike, I would not ride it until I am 100% sure it is fixed for good. | ||
| Mmcn49 |
I would also look at the linkage in the handle at the adjustment wheel, where the lever pushes the plunger on the master cylinder. >>> Did that, but as I’m still at work didn’t take anything apart. The handle & linkage are fine and the rubber dust seal is not torn. Did the lever still have a spring action to return forward, or did it just go floppy? >>> Yes. There was a definite pucker factor, but I kept pumping it most of the way down. It wasn’t floppy and sprung back on its own. With the absence of weeps & leaks, (I’ve triple checked) it’s probably something in the master cylinder. Will bleed the system, check for leaks and see if I can glean anything from the manual or parts book diagram, before taking anything apart. | ||
| Kalali |
If you look at it logically, assuming no leaks and a full reservoir, then when you pull the lever, the master cylinder piston is not "compressing" the fluid. Looks like a rebuild is in order. | ||
| Mmcn49 |
Except that force is now being applied to the pistons in the caliper. Now its working like it should. | ||
| Kalali |
That's true but remember that if the piston or the cylinder in the master cylinder is scored, it will allow fluid to bypass the piston thus not compressing the fluid. The intermittent nature of the problem is intriguing though. | ||
| Brumbear |
Check the fluid level if its good bleed it if there is no air GET A NEW MASTER CYL it's your life |
