Bleeding air out of brakes

[FlyDave]

Last  year when we changed the brake pads in my plane (Bravo with dual brakes) we had a problem getting the left brake on the left side to come back up completely. It was soft after bleeding it quite a bit but finally came mostly back up - but never completely right.

Over the time between then and now the brake would get soft, I'd add fluid and it would come back up but was still a little soft. A few weeks ago it got really soft and would not come back up.

I read all about other peoples brake woes on MooneySpace as well as brake issues on other sites and attempted numerous resolutions on soft/spongy brakes. I tried every solution I could find but to no avail. That friggin' left peddle on the left side was not coming up!

I reviewed the issue with a friend (partner in another plane) and he said "let's try an old motorcycle trick".

An air bubble will move freely across a consistent surface but where the shape of the inside of the brake line changes a bubble will stop - especially when that change in internal brake line is at a high point in the system or a portion of the system.

He got under the wheel well and found the point where the flexible hose goes into the rigid metal brake line (see attached pic) and said let's bleed it here. I got in the pilots seat, pumped up the left brake peddle and he eased the fitting loose and tightened it back up when I had the peddle completely pressed. We did this 2 times and voila, nice stiff brake peddle that had been soft all the way to the floor.

I hope this helps other people get past similar brake problems. It was quite frustrating - there had to be a solution and there is (at least for me).

 

Happy Braking!

 

Dave

[Piloto]

Looks like a bubble was trapped in the line close to the master cylinder. Thanks for the tip. Another way of bleeding the brakes is by pumping hydraulic fluid thru the caliper fitting. The bubbles will come out on the reservoir in the tail cone. I use an oil squitter with a hose as a pump. Works pretty well.

José

[FlyDave]

Looks like a bubble was trapped in the line close to the master cylinder. Thanks for the tip. Another way of bleeding the brakes is by pumping hydraulic fluid thru the caliper fitting. The bubbles will come out on the reservoir in the tail cone. I use an oil squitter with a hose as a pump. Works pretty well.José

Jose,

I pumped over a pint of brake fluid up from the capiler but it didn't make a difference. The bubble was trapped by the heavier fluid and was not moving.

Dave

[Guitarmaster]

Awesome!!! Thanks for sharing!!

[Mooneymite]

I love stories with happy endings.

That's a good tip....thanks for sharing.

[cliffy]

Cool tip -never knew it

[Guest]

Over time Mil H 5606 hydraulic fluid will thicken and become almost syrupy. This can cause troubles with bleeding as well as draggy brakes.

Sometimes I will use the 2 person bleeding method to pump old fluid out through the calliper bleeder screw until the fluid is thin.

Clarence

[Alan Fox]

I have had good luck with compressing the calipers in and pushing everything back up through the reservoir...pumping them out and then compressing them again , generally after three or four cycles the brakes are rock solid....all the air gets pushed back through the system and exits through the reservoir...