Master cylinder bleeders: How much air pressure?

[Schurkey]

With ^^^ this style adapter, you aren't even affecting the fluid in the RESERVOIR, it's pumping pressurized fluid directly into the master cylinder bore. You CANNOT use "air" to bleed brakes with this system.

I've been using a Motive garden sprayer type since 2014 at 10psi with flawless results. I only use the fluid in the reservoir because supposedly pumping fluid from the sprayer puts more air in the fluid. I'm a road racer, so I have to trust my brakes with my life and this has been doing the trick just fine.

Any decent master cylinder adapter will discharge the pressurized fluid BELOW the fluid level in the master cylinder reservoir if (big IF) the fluid level in the reservoir is high enough. Squirting fluid into fluid isn't going to entrain air. Squirting fluid into air, so that it splashes into the fluid already in the reservoir would cause air bubbles in the fluid.

Either you're blowing air into the fluid already in the master cylinder, OR you're not using a good master cylinder adapter, OR the fluid level in the reservoir is lower than optimum for the purposes of bleeding the brakes.

This does get a little tricky, because with disc brakes, the level of fluid in the master cylinder is intended to go down as the pads wear--it's one simple, easy way to keep track of the wear on the pads. But when I bleed brakes, the first thing I do is to fill the reservoir so that the fluid under pressure from the pressure bleeder isn't splashing into the reservoir and making "foam".

I'm not arguing that what you're doing is "working" for you. I'm saying it could work (theoretically, at least) better if you did it right. MAYBE it would even work better in a functional way. No way to know until you try it.

 

[Supercharged111]

No arguments that what I'm doing is not ideal, but it has been working so far. I think the super bleeder you're referring to is out of my price range.

 

[Schurkey]

I think the super bleeder you're referring to is out of my price range.

This is our philosophical difference.

You see a diaphragm-style bleeder as a "super bleeder". I see it as the only way to do pressure-bleeding properly

You see the garden-sprayer bleeder as a viable, less-expensive alternative, I see it as a guaranteed way to put humidity (water contamination) into the brake fluid. Clearly the "garden sprayer" would work better in Phoenix AZ than in Miami based on ambient humidity.

 

[Supercharged111]

Again, I road race. I put way more strain on my brakes than 99.9% of the people on this board. Moisture lowers the boiling point of the fluid, so if anyone were to have problems with the garden sprayer it should be me. The real world difference must be damned insignificant.

 

[454cid]

Again, I road race. I put way more strain on my brakes than 99.9% of the people on this board. Moisture lowers the boiling point of the fluid, so if anyone were to have problems with the garden sprayer it should be me. The real world difference must be damned insignificant.

Yeah, given the limited surface area, and time, I don't see moisture contamination to be a significan't risk here. The other device still requires a person to open the cap. This isn't AC refrigerant.