Front brake lever was firm, now it's loose until the midpoint, tie with or without reservoir open?

[No H2O]

Front brake lever has been working fine for a few weeks, today when I grasp the lever there's only "play" until the halfway point, then there's the usual firm grip.
I assume I have air in my brake line.
I'm going to tie the lever tight overnight but does that need to be done with the reservoir open or keep the reservoir shut?

 

[Jersey Big Mike]

When was the last time you checked the calipers? A sticky/stuck piston can create this type of action as well.

 

[No H2O]

When was the last time you checked the calipers? A sticky/stuck piston can create this type of action as well.

Haven't checked at all. I usually only do that when I change pads but the pads appear to be ok.
Anything to be concerned about safety-wise?

 

[Sven]

Keep the rez on. Rubber diaphragm can move a lot so no need to uncap. Say the overnight brings no joy. Hold the lever tight, break the banjo bolt at the master, retighten the banjo before the lever reaches the grip. Pump up... we have a hard lever again?

 

[Mr. Wright]

The hand brake master cylinder, I.E., the hand brake, on the 04's, will suck air if they are just a little bit low, and you squeeze it while it's sitting on the kick stand. These were changed in 05. Check the fluid level, and while you have the cap off, slowly squeeze the handle. You will see the air bubbles come through the port. Keep squeezing it slowly till the air stops. Top off the brake fluid, and put the cap back on.
DOT 5 brake fluid.

 

[No H2O]

Keep the rez on. Rubber diaphragm can move a lot so no need to uncap. Say the overnight brings no joy. Hold the lever tight, break the banjo bolt at the master, retighten the banjo before the lever reaches the grip. Pump up... we have a hard lever again?

I assume that's the bolt that bolts to the reservoir itself and not the one that's on the line?

The hand brake master cylinder, I.E., the hand brake, on the 04's, will suck air if they are just a little bit low, and you squeeze it while it's sitting on the kick stand. These were changed in 05. Check the fluid level, and while you have the cap off, slowly squeeze the handle. You will see the air bubbles come through the port. Keep squeezing it slowly till the air stops. Top off the brake fluid, and put the cap back on.
DOT 5 brake fluid.

So yesterday when I first got back I started squeezing the lever with the cap off and air was coming through the port but not strong enough to penetrate the fluid and release into the atmosphere. So I started squeezing quickly to make the bubbles explode out through the top. That didn't have any effect.

Overnight I tied the lever to the throttle with the cap on, this morning I squeezed the handle a few times and that got it a lot better than it was.

The fluid in the reservoir was about 1/8" below the top rim. I assume I'll need to fill it all the way to the rim? (the challenge will be securing enough old rags directly under the reservoir to absorb any overflow spillage)

 

[Sven]

Banjo feeds the brake line. Brake line is anchored down with a banjo bolt. Break the seal of the crush washers so that kind of pressure can bleed thru that crack. You do not want to spin the bolt even a 1/4 of turn open. Let the hydraulic work the push of the bubbles out. Ever see a ball fountain; for a better term?

Imagine this is an air bubble. It just tumbles as the fluid is being pushed out of the brake caliper nipple say. But you never can get that hard pedal after all is said and done. Now look at the brake hose end fitting. See how that bubble can stay about at the ceiling of the end fitting and have the air bubble tumble just sitting in one spot? Position bike as per Mr. Wright.
https://content.speedwaymotors.com/...RL_L_6816e7c8-954d-46ee-bf09-b9aa1c78338b.jpg

That's where the bubble hides. Make sense?

Fluid Level Compensation Fill Factor:
1. Pads wear down.
2. Pistons move out.
3. Fluid drops in rez.
4. Fill factor fill is so much times pushing the pistons back with added fluid = PAINTS A New Picture on the paint scheme LOL

 

[No H2O]

Good details, thank you

 

[Srodden]

Banjo feeds the brake line. Brake line is anchored down with a banjo bolt. Break the seal of the crush washers so that kind of pressure can bleed thru that crack. You do not want to spin the bolt even a 1/4 of turn open. Let the hydraulic work the push of the bubbles out. Ever see a ball fountain; for a better term?

Imagine this is an air bubble. It just tumbles as the fluid is being pushed out of the brake caliper nipple say. But you never can get that hard pedal after all is said and done. Now look at the brake hose end fitting. See how that bubble can stay about at the ceiling of the end fitting and have the air bubble tumble just sitting in one spot? Position bike as per Mr. Wright.
https://content.speedwaymotors.com/...RL_L_6816e7c8-954d-46ee-bf09-b9aa1c78338b.jpg

That's where the bubble hides. Make sense?

Fluid Level Compensation Fill Factor:
1. Pads wear down.
2. Pistons move out.
3. Fluid drops in rez.
4. Fill factor fill is so much times pushing the pistons back with added fluid = PAINTS A New Picture on the paint scheme LOL

Good explanation Sven ! Air tends to hide in a cavity.

 

[heybaylor]

calipers sticking, moves the pistons to engage shoes, stretches rubber seals , they act like springs pull the pistons back a little.
when clean the rubber seals let the pistons move and stay where they contacted shoes,
pop the pistons, clean the calipers problem solved.
tying the brake lever overnight just might let the pistons stay at the contact point , but is a bandaid shade tree fix ,(sometimes)

 

[Sven]

calipers sticking, moves the pistons to engage shoes, stretches rubber seals , they act like springs pull the pistons back a little.

The rubber does not stretch; being locked in a groove. The rubber moves a little out [from under] the groove ever so slightly. Because rubber has memory like a spring, it moves itself back into the groove, i.e., is now square and back to memory as if the spring was in a static position. This pulls the piston back with it = No pad drag.

... when clean the rubber seals let the pistons move and stay where they contacted shoes,
pop the pistons, clean the calipers problem solved.

When the groove is clean, where no contamination is under that tiny gap of quad-ring movement, this is where you concentrate on the caliper cleaning. This area needs to be clean of any crystallized residue out from under the groove. This crystallization under that quad-ring, lifts the rubber so the piston can no longer be pulled back by the quad-ring returning to memory = Pad drag.

... tying the brake lever overnight just might let the pistons stay at the contact point , but is a bandaid shade tree fix ,(sometimes)

This is where there is a [tiny] fill hole where fluid drains into the master's piston bore hole so when the pads wear down, the piston moves out, is where that oil fills that void behind the piston. The other [large] hole is where the master closes that hole and compresses the fluid hydraulically. That larger hole is the relief hole that lets the compressed fluid return back up [faster] out of that hole... like a geyser. So any bubbles on the hose side is going to rise back up [overnight] and settle in the banjo say, or the highest point between master and hose. Upon lever release, this is going to be pulled out via the large hole; is the theory of the morning zip. There is where you're chasing the champagne size bubbles that are all up and down the brake line. This is my understanding.