Soft Brake after Rain
 

Hi everyone, so I have a soft front brake lever after riding thru hard rain and puddles on the street for about 20 minutes. I had just replaced the brake fluid and bled the brakes. I even had to zip tie the brake overnight to get all the air out but in the end I had a real firm brake for about a week. Now it feels like its at 70% braking power. The first couple of inches that I used to slow down slowly now don't do anything at all. I can get it to brake hard but I have to squeeze the lever all the way to the grip. Before I could make the front tire chirp using half or maybe 2/3rds of the brake.

Any ideas what it could be? Moisture in the fluid? Caliper seals? It has no leaks at all from the cylinder to caliper. I filled it 2 weeks ago and checked it last night and the cylinder is still full.

Sorry for the long post. Cheers,

I know that when a rotor is wet you get diminished braking but the water heats off pretty quickly. Another thing it could be is that there was some oil that stuck on your rotor. Could you also have some debris on your pads? Just a few ideas. If it were me, I'd start by scrubbing the rotors with soap and water then washing it off and see where that gets me. Good luck with your problem and I'm sure you'll get more and better opinions than mine.

Mike

Neo,
Is the brake issue only after a rain?
It sounds unusual but not entirely without reason that if this is so that the brake fluid is contaminated.
Is the the fluid flush all that you did to the bike, and if so for what reason.
The more information that you give can help to come to a better overall idea of what is wrong and help us give you a better idea of how to fix it
M.j.n.

Usually what happens, is if its raining you are too overly cautious using the breaks and they remain cold when you use engine brake to slow down. While you don't skid or wipe out, you leave your brakes cold, and when wet, they don't work so well. Keep the pressure on and heat those brakes up and they will work better.

Now if it lasts more than a day, it probably is some road oil on the caliper, have you hit it with brake cleaner?

This started after that ride in the rain but its been constant now rain or no rain. I flushed the fluid when I changed the fork oil seals. One of the caliper bolts would not come off so I decided to disconnect the brake line and flush the fluid instead. It was braking really good for a week. Now for the past 10 days Ive had this issue. I checked and rechecked and no leaks at all in the system. I zip tied the brake lever the past 2 nights to get the air out, that worked when I flushed the fluid, but hasnt helped with this.

Your caliper might be sticking. Check for free movement on the sliders.

When you bleed the brakes you can old take a rubber or plastic screw driver and tap the line at the banjo nut and caliper to get remaining air out, although if there was air it wouldn't be good for the first week to begin with. Sticky caliper might be the issue

Neo
It is highly unlikely that what you are describing is from a soiled rotor, if that we're the case the breaking would be deminished but it would not cause the increase in master cylinder piston travel that you describe.
Also the chances of this being from a sticking caliper is low as this would cause the effects that you are seeing but once again the travel to the bar with the lever would most likely not happen
It sounds like you may have a small air leak in your system, I would most likely guess that it is at the point that you disconnected the brake line from the caliper, when you did this did you make sure to clean the banjo bolt surfaces well before you re assembled the like, also did you replace or reuse the copper banjo washers. Hope this give you a starting point.
M.j.n.

mjn, I made sure everything was clean but I did not replace the copper washers. I figured if it didn't leak fluid it wouldn't leak air, or could it?

Did you reuse the copper washers or now have no washers at all?