Brake Bleeder Screw Questions.

[Flywheel]

I'll be getting some SS lines done to replace the old stock lines and after re-reading the service manual/how-tos, I was struck by a few questions:

--The bleed screw needs to be loosened in order to push/vacuum the old fluid out (through the body of the screw).

--The screw is a compression fitting and the threads themselves don't directly seal the system.

Some guides suggest removing the screw and wrapping the threads with teflon tape (preventing air from entering the caliper during bleeding. Wouldn't the brake fluid out drain completely if you did that? If so, how far can you loosen the screw before it starts leaking? Do air bubbles automatically form when you open it?

Thanks in advance. I've bled brakes on a few bikes before, I'm just looking to understand it better.

 

[SpikedLemon]

You'll need to drain the lines completely anyway. I recommend getting speed bleeders; it saves you from re-tightening the bleeder when you release the brake.

Many of the bleeder screws come with dry threadlock already pre-applied and just cracking it a little will open them (1/2 turn)
Teflon could work; I've never used it. Teflon stands up to a lot.

 

[Flywheel]

You'll need to drain the lines completely anyway. I recommend getting speed bleeders; it saves you from re-tightening the bleeder when you release the brake.

Many of the bleeder screws come with dry threadlock already pre-applied and just cracking it a little will open them (1/2 turn)
Teflon could work; I've never used it. Teflon stands up to a lot.

True. I've installed stainless lines before too. Just curious about the screw/caliper interface.

 

[bboySushi]

Bleed screw:

The tapered end fits into an equally tapered cut. When you unscrew it you are no longer plugging that space, and the oil moves up through that bored hole through the center of the screw and out the top. When the screw is open, yes, the bottom part of the thread is creating a seal but at that point the system the lines don't have much pressure. Fluid will flow through the path of least resistance - through the hole in the middle. Once the screw is closed, the tapered area is a compression fit and the threads are no longer part of the equation.