Bleeding the Brakes

[karaka29211]

Having read the Finish Manual instructions on bleeding the brakes, I am confused. When trying to pump brake fluid up from the open bleeder valve and there being no vent at the cylinder end, how does the air get expelled without there being a vent at the top? This Youtube video highlights the vent on a similar system.
https://www.youtube.com/watch?v=bZlq87VXybU&t=303s

[Andy]

When the master cylinder piston is fully retracted there is a passage open to the reservoir. This port closes when the piston moves from the fully retracted position.

I would expect any fluid pumped in at the bleeder valve to pass through the master cylinder, fill the tiny reservoir, and spill on the floor.

Unless I had specific instructions to the contrary I'd insert a close fitting tube in the top of the reservoir to catch the fluid.

The brake system on the Carbon Cubs is very simple and, unlike my PA-28 which has 5 linked master cylinders, should be quite easy to bleed.

[karaka29211]

Thanks for the reply, please confirm the meaning of having the master cylinder piston "fully retracted"- does that mean that the toe brakes need to be depressed while the brake fluid is applied under pressure?

When the master cylinder piston is fully retracted there is a passage open to the reservoir. This port closes when the cylinder moves from the fully retracted position.

I would expect any fluid pumped in at the bleeder valve to pass through the master cylinder, fill the tiny reservoir, and spill on the floor.

Unless I had specific instructions to the contrary I'd insert a close fitting tube in the top of the reservoir to catch the fluid.

The brake system on the Carbon Cubs is very simple and, unlike my PA-28 which has 5 linked master cylinders, should be quite easy to bleed.

[Andy]

Thanks for the reply, please confirm the meaning of having the master cylinder piston "fully retracted"- does that mean that the toe brakes need to be depressed while the brake fluid is applied under pressure?

The master cylinder port is open to the reservoir when the brake pedal is not pressed and the maximum length of the piston rod is exposed outside the master cylinder body. This is how the fluid in the reservoir is allowed to enter the brake system. As the pedal is pressed the reservoir port is closed and piston pressurizes the fluid in the brake line.

(In hindsight I can see that "retracted" may not have been the best word to use but it does describe the position of the piston in the cylinder.)

[Pete D]

Correct, you can add a hose into a can off the revivor tube (with the cap out) and pump up from the bottom until you have fluid overfilling through that hose into your can.

Andy, I agree with you, the PA28 5 master cylinder system is one of the most complex brake bleeds I've ever seen!

When the master cylinder piston is fully retracted there is a passage open to the reservoir. This port closes when the piston moves from the fully retracted position.

I would expect any fluid pumped in at the bleeder valve to pass through the master cylinder, fill the tiny reservoir, and spill on the floor.

Unless I had specific instructions to the contrary I'd insert a close fitting tube in the top of the reservoir to catch the fluid.

The brake system on the Carbon Cubs is very simple and, unlike my PA-28 which has 5 linked master cylinders, should be quite easy to bleed.