What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Trouble bleeding air from the brake system

B

BigJohn

Well Known Member
I tried all afternoon to put the brake fluid in the system and get rid of the air. Needless to say I lost the air war! I followed the Matco procedures exactly - several times. I was using the pressure pot that I borrowed from my friendly FBO. It drives the fluid in through the bleeder at about 10 psi.

On the first try I was all excited as I watched the red stuff work its way through both master cylinders and out into the reservoir. Thought I had it made. Then the little sneaky bubbles started working their way out of the cylinders and into the tubes. And no matter what I tried, the bubbles stayed. Tried pumping more fluid upward through the system, no go. Tried old fashioned bleeding from the top down, no go.

How did you earlier guys ever get the air all out?
 
air bubbles

The tank must not be pressurized till just before you bleed the brakes. If it sits pressurized air enters the oil then when you bleed the brakes a few minutes later the air starts coming out of the oil leaving bubbles in the lines.
I have made this mistake before and took awhile to figure out where the air was coming from.
Ric
 
First time

I bled from the bottom up per Matco; got all the air out of the master cylinders but then some reappeared ABOVE the cylinders. Apparently it worked its way on up ito the reservoir. Second time, after fixing seepage, I could NOT get flow up through the system. An old-time A&P looked at the system and said "You'll never get fluid up through 4 master cylinders!" He bled top down, with about 10 psi airpressure put into the system, and that worked just fine. Just check often to be sure there's still fluid in the reservoir.

Wayne 120241/143WM
 
yankee-flyer said:
I bled from the bottom up per Matco; got all the air out of the master cylinders but then some reappeared ABOVE the cylinders. Apparently it worked its way on up ito the reservoir. Second time, after fixing seepage, I could NOT get flow up through the system. An old-time A&P looked at the system and said "You'll never get fluid up through 4 master cylinders!" He bled top down, with about 10 psi airpressure put into the system, and that worked just fine. Just check often to be sure there's still fluid in the reservoir.

Wayne 120241/143WM
Click to expand...

I don't know what was causing your trouble but the old timer was wrong this time. It does work from the bottom up. That is why the company (Matco) that manufactured the brakes, and the people that wrote the construction manual tell you to do it from the bottom up.
 
I just did my brakes again not too long ago as my parking brake was leaking and had to disconnect all lines. I just bought a cheap pump for transmission fluid at the local auto store and pushed the fluid from bottom to top. It did not even need bleeding, all four pedals were as stiff as it could get and has not gone soft since I did it (40+ hours)

It was my second time using this type of pump and it was very easy, just have some one watch the reservoir as I pushed too much fluid and it over flowed on top.
 
One final test... before reaching for that cold brew...

When you think you are done, the brakes work, pedals feel firm, and the wheels won't turn with brakes applied, release the pedals and check for drag.

After releasing the brakes, if the wheels do not spin freely, guess what, you still have bubbles in the line somewhere. The puck is still extended, thanks to an air bubble.
 
rvbuilder2002 said:
I don't know what was causing your trouble but the old timer was wrong this time. It does work from the bottom up. That is why the company (Matco) that manufactured the brakes, and the people that wrote the construction manual tell you to do it from the bottom up.
Click to expand...

Scott,

I believe you, and apparently I am doing something wrong. There are bubbles of air an inch or two long in the top of the loops between the pilot and copilot sides. They refuse to move, no matter how much fluid I pump through from the bottom. Can you give us a hint on the proper procedure that will work here?
 
Is it ok to offer some ideas?

BigJohn said:
There are bubbles of air an inch or two long in the top of the loops between the pilot and copilot sides.
Click to expand...

Is it possible that some remnant from flaring/cutting alum lines remained in the line and has now flowed into a critical junction, preventing fluid from passage?

Picture a coronary occlusion.

If all else fails, you may have to open/disassemble and/or check EVERY aspect of the system to find the chunk of "flotsam" that's blocking the fluid. EVERYTHING include brake cylinders that have tiny orifices.

Some people recycle brake fluid and to those I caution to run the recycled fluid thru an auto body paper paint strainer.

You could always build the device Ernst Freitag made in 2005. Here is a photo of Ernst's clever design.

braikebleedingpressurec.jpg


His post is somewhere on this website but if you send me your email address I will email you his complete article.

Hope this helps.
 
MrNomad said:
Is it possible that some remnant from flaring/cutting alum lines remained in the line and has now flowed into a critical junction, preventing fluid from passage?

Picture a coronary occlusion.

If all else fails, you may have to open/disassemble and/or check EVERY aspect of the system to find the chunk of "flotsam" that's blocking the fluid. EVERYTHING include brake cylinders that have tiny orifices.

Some people recycle brake fluid and to those I caution to run the recycled fluid thru an auto body paper paint strainer.

You could always build the device Ernst Freitag made in 2005. Here is a photo of Ernst's clever design.

His post is somewhere on this website but if you send me your email address I will email you his complete article.

Hope this helps.
Click to expand...

Barry, thanks for the suggestions.

I don't believe there is anything blocking the flow. Fluid travels freely and overflows the reservoir when pumped in the bottom. It's the air that doesn't move. Inexplicibally it moves a little but stays put in the line.

I AM recycling the fluid and straining it through a very fine paint filter.

My email is [email protected]. Please send the article.

John
 
I make my bleeders out of one or two gallon garden sprayers. I've made half a dozen over the years and they work fine. Cut off the hose near the sprayer wand and epoxy on a length of vinyl hose (clear so you can see). Bleed slow. Too fast causes problems. Those stuck bubbles in the upstream lines can be worked out by hand tilting the hoses. Tapping the calipers & cylinders with a wrench or something while bleeding helps dislodge bubbles. I just bled my 10 bottom up and it worked fine the first try. Sometimes though it will take several tries. I have spent whole days on something like a Piper Arrow. Have actually had to cycle the gear while bleeding. A little jiggle on the pedals while bleeding can help also.
 
How about connecting a long piece of .25" (or suitable size) hose to the bleeder screw and put the other side into your reservoir and keep pumping and watch the fluid get cycled thru. This will make bleeding easy and perhaps the bubbles make themselves thru eventually.
 
disconnect the lines

I disconnected the brake lines between the pilot and copilot master cylinders and bled one side, then connected the lines and bled the other side.
Joe
 
BRAKE BLEED

I HAVE HAD TO BLEED SOME MATCO BRAKES FROM TOP DOWN. USUALLY ON A RV-4 THAT HAS THE MASTERS MOUNTED UPSIDE DOWN. I INSTALL A FITTING ON THE RES. AND PRESSURIZE, THEN OPEN EACH BRAKE BLEEDER. MAKE SURE BOTH PEDDLES ARE PULLED FULLY BACK.
 
DENMACRES said:
I HAVE HAD TO BLEED SOME MATCO BRAKES FROM TOP DOWN. USUALLY ON A RV-4 THAT HAS THE MASTERS MOUNTED UPSIDE DOWN. I INSTALL A FITTING ON THE RES. AND PRESSURIZE, THEN OPEN EACH BRAKE BLEEDER. MAKE SURE BOTH PEDDLES ARE PULLED FULLY BACK.
Click to expand...

That's the way Piper installs them on all of the pa 28 models. And you do bleed them from the top down with no problems. When I rebuilt my master cyl's in my Piper (5 of them) it took me about ten minutes to bleed the brake system by myself..................

When they are mounted "up side down", to rebuild them all you have to do is remove the one bolt on the end of the shaft and remove the snap ring and pull the entire plunger out of the body without removing any of the fluid lines. I think it is just a better way of installing the cyl's.

Why did Van mount them the way he did on the 6,7 and 9???
 
Last edited:
Just to let you know....

I think (fingers crossed) I finally got all the air out of the system. But it wasn't easy. When pumping fluid from below, those darn bubbles would come down the tubes, appear to enter the bottom of the clinders, but not come out the top. Air seems to get trapped in the cylinder. No amount of tapping, repositioning, pumping, etc. would push those bubbles out. Finally expelled the air by positioning the bubble right at the bottom of the cylinder, then loosening the tubing connection enough to let out the air and some fluid.

Man! I hope those bubbles don't come back tomorrow!
 
You must log in or register to reply here.
Back
Top