Front brake Frustration

[OklahomaPomade]

One more brake question, when you pull the brake lever, it puts fluid behind the piston which pushes it out. What makes the piston go back in? I assumed that when you let go of the lever, that the fluid kind of sucks it back in, but if this were the case, then pumping the lever with the caliper off the bike, wouldn't pop out the piston, and it does.

The piston doesn't really go back in, merely pressure on it is relieved. This all goes back to that little hole on the master cylinder piston. It is a relief, of sorts (in fact, I think that's what it's called). The lever pushes the pistion, the piston moves the fluid, the fluid moves the caliper piston. The little hole allows fluid to "relieve" back into the line so it won't lock up.

As far as your other question, heat should have little effect. Fluid will not compress like air does but it will expand and contract somewhat. The heat of day though, would have very little effect.

I cleaned the little hole in my lever piston with a HVAC tool called an Oriface Drill (very, very small). I couldn't even SEE the hole until I took a wire wheel to it!

 

[OklahomaPomade]

Sure did. I paid special attention to that hole. If I have the plastic reservoir off and squeeze the handle, I can see the piston moving back and forth in the hole.

That ain't it. It is on the piston itself. I can't remember if it's under the brass disk or under the rubber cap...hmmm, strange...I just did this 1 month ago.:-s

 

[usin13]

Knock on wood

Knock on wood

Not understanding in the past that the little divot was actually the return hole I breezed right past it. Tonight I cleaned it thoroughly. As you may have suspected already, it was blocked. I took the end of a High E guitar string and cleaned it out really well. Then I rebled the system. What do you know, I'm an idiot.
It is working fine now. I have a slight drag on the wheel when I spin it, which I have read is normal, and the best part is, the drag doesn't change after I've pumped the lever a couple of times. So, keep your fingers crossed and knock on wood that it is remedied now.

I'm very happy because tomorrow is my Birthday and I really wanted to ride on my birthday.

Thanks for letting me waste your time with a question that has already been answered a million times. Don't block me from your lists to read posts from, I'm really a lot smarter than this made me look!!!! ;-)

Thanks again.

 

[OklahomaPomade]

I don't block people...Somebody else helped me with the same problem not long ago. Pass on your knowledge.

 

[Road_Clam]

The piston doesn't really go back in, merely pressure on it is relieved. This all goes back to that little hole on the master cylinder piston. It is a relief, of sorts (in fact, I think that's what it's called). The lever pushes the pistion, the piston moves the fluid, the fluid moves the caliper piston. The little hole allows fluid to "relieve" back into the line so it won't lock up.

As far as your other question, heat should have little effect. Fluid will not compress like air does but it will expand and contract somewhat. The heat of day though, would have very little effect.

I cleaned the little hole in my lever piston with a HVAC tool called an Oriface Drill (very, very small). I couldn't even SEE the hole until I took a wire wheel to it!

The piston does retract. The m/c hydraulic forces work BOTH ways. The return spring in the m/c pushes the m/c piston which creates a small amount of "reversed" hydraulic flow, which slightly draws the caliper piston away from the brake rotor. It only retracts the piston about .030"