Brake bleeding

[peter425]

Tthe  left brake pedal in my 231 lost all hydraulic fluid. There was evidence that fluid had leaked past the piston o-ring in the brake assy. I am replacing the o-ring and I am back bleeding the brake system through wheel cylinder bleeder valves using pressure pot. Using this method is there a need for pumping the brake pedals? Service manual states that the brake pedal should be "pulled back" (section 12-20-05).  Any helpful suggestions out there from folks that have experience with brake bleeding mooneys. Does raising nose wheel off the ground help? What will be indication that the master cylinder needs servicing? Thanking you in advance for your help. peter lamberty N322DB

[jetdriven]

We have been fooling with the brakes for a year now. We let all the fluid run out of the left side overnight, and since then, the pedals are spongy.  Dan at LASAR said to put the tail on the ground to assist bleeding. We are going to OH the master cylinders and bench bleed them, then bleed with the tail on the ground this time to get it right on.

[OR75]

what do you mean by putting the tail on the ground ? does it really make a difference in containers levels ?

[jetdriven]

You tie the tail down as low as you can get it or hold it down whle bleeding the brakes. I was told this angles the master cylinders enough to get the air purged better.

[testwest]

Peter, if you wind up losing the ability to make pressure after replacing the o-rings and servicing the fluid in a short period of time down the road, it is definitely time to replace that master cylinder. This happened to us, we kept losing one of the brakes, the master cylinder o-rings were replaced, it would work for awhile, then fail again. Once the master cylinder was pulled out, scoring marks were easily seen in the barrel, which were prematurely failing the o-rings. One new master cylinder, problem gone.

 

If you service the brake fluid yourself, a pressure pot with a good bit of 5606 is helpful. The brake line has a high point in the wheel well and I am pretty sure one could trap an air bubble in there, leading to the spongy brake feel. Pushing in a bunch of fluid "should" alleviate that problem.

 

If you have a cooperative AMT, you can do a lot of this yourself. It is messy work, but you certainly gain a better knowledge of your airplane by wrenching on it.

[Bolter]

I chased a brake problem for over a year.  I would be great with brakes, and then one would go soft on the pilot side, sometimes both.  The co-pilot brakes would stay firm, as the fluid would drain from one set of lines before the other.  But there was actually a leak found on the co-pilot brakes as well, which seemed unintuitive at the time.  In the end, we replaced the o-rings in all 4 master cylinders and replaced some lines.  All were old, probably original from 1983.  Each item done one at a time, always convinced we found the problem.  The reality, and my point, is that you may have accumulated multiple leak points.  Having all belly panels removed helped to find some pin hole leaks during bleeding.

 

-dan

[jetdriven]

FWIW in a week we are stripping down the master cylinders, honing and overhauling them, and then bench bleeding the master cylinders and then bleeding the brakes on the plane. Our brakes have been spongy for a year since we let the fluid run out while we fixed a brake caliper.  I will report back with findings.

[N601RX]

I rebuilt all 4 of my master cylinders last year and did not have any problems with the bleeding as others have reported.  The fluid flowed through the system easily.  Here is some other info I dug up in the process.  The Gerdes A-110-37 and Cleveland 10-49 are the same cylinders.  Cleveland bought out Gerdes sometime in the late 70's.  Spruce sells a repair kit that will work with either of these.  I  have some spare master cylinders if anyone needs one.  Also the factory drawings for the copilot brakes allows substituting the Gerdes or cleveland cylinders in place of the original Paramount cylinders on older planes.

 

https://www.aircraftspruce.com/search/search.php?s=199-516&x=0&y=0

[OR75]

fwiw, i did bleed my brakes this afternoon.

used a plastic syringe fitted with a 1/4 in OD clear vinyl tubing. you may need to use a step down larger clear vinyl tube if the syringe is large (helps not to have to refill it too many times). cost of syringe was 1.50 at tap plastics. vinyl was 12 cents a foot.

i removed the brake fluid can and adapted a clear vinyl tubing to an overflow beaker.

open the bleed valve several turns and push fluid up slowly.

if the 5606 does not move, you need to go inside the plane and move the brake pedals by hand is fine.

repeat until there are no more air bubbles going through the tubing into the beaker.

close the bleeding valve. change wheel. repeat above. the brakes work great.

it is a messy job, so dress accordingly.

[jetdriven]

FWIW in a week we are stripping down the master cylinders, honing and overhauling them, and then bench bleeding the master cylinders and then bleeding the brakes on the plane. Our brakes have been spongy for a year since we let the fluid run out while we fixed a brake caliper.  I will report back with findings.

Overhauled master cylinders, bench bled, installed, and bled again. No dice, the brakes still suck. Any ideas?

[bumper]

Overhauled master cylinders, bench bled, installed, and bled again. No dice, the brakes still suck. Any ideas?

A small garden sprayer can be converted into a *power* brake bleeding pot. This allows you to get a fair amount of volume which helps remove air bubbles from any high spots.  A 1/8" pipe thread nipple with clear overflow tube takes the spent fuid from fluid reservoir into a jar so you can tell when fluid is clean and bubbles stop. If the brake hose is not at or near the top of the caliper during bleeding, then it's good to remove and position caliper so hose is at top - - this helps expel any air in the caliper. -  Be sure the use a suitable clamp to keep piston in place while bleeding or you'll really have a mess! 

[romair]

when I had my brake problem, I asked Don Maxwell - this is one of the things he considered

 

"it
could be the statoseal inside the master cylinder. This seal floats and is
sealed when you apply the pedal making the fluid go to the wheel cylinders.
When you release the pedal, this seal floats and allows the fluid from the
wheel cylinder to return to the reservoir"

 

I am not sure how this plays in light of overhauled cylinders, but just a thought?

Stefan

[N601RX]

The kit I mentioned above comes with a new statoseal.  The Cleveland cylinders uses a small spring to keep the statoseal seated against its sealing surface. 

[N201MKTurbo]

I have found that if you pump your brakes while up high, say above FL100 it will work all the air out of the system. Besides what else do you have to do while motoring along up there, it'll give you something to do.

[OR75]

Overhauled master cylinders, bench bled, installed, and bled again. No dice, the brakes still suck. Any ideas?

 

 

Jetdriven:

see the description I did above.

 

In summary:

 

Remove the hydraulic reservoir and sink the pvc tubing into a hydraulic beaker (so you can see the air bubbles out and when the system breathes in, it will fill with hydraulic ratehr than air.

 

It can be done by 1 person but much easier to get someone to help: while one is injecting fluid up the brakes, other person can monitor the beaker and shake the brake pedals so tjat the fluid moves. 

[isaacpr7]

I just finished doing my first anual inspection and the AD for the squirly nose gear was applied. This completely fixed the problem; however, when I tried fast taxying to test it out I noticed it pulled to the right. I found this to be weird because it never did this before. I then remembered that the left caliper had to be bled because it leaked fluid during tire removal. It took a bunch of fluid to service the system. After doing some research I suspected that the aircraft was pulling to the right because the left caliper still had some trapped air in it like most of you guys have suggested. What I ended up doing was pumping the brakes multiple times during take off nose high attitude (without stalling off course) and this seemed to work because it does not pull to the right anymore and the rudders are even again.

[Mooneymite]

I try to avoid having to bleed the system. At each annual, I drain about an ounce of the old brake fluid from each brake and refill the reservoir. Maybe not as good as a complete flush and refill, but a lot simpler.

[Mckipper]

 

 

 Rebuilt all the master cylinders 12 months ago - recently started with the left peddle soft again - eventually traced the fault to the Park Brake Value - new o rings and problem solved - amazing how quick the fluid drained through the park brake value.

 

More relevant - when we rebuilt the masters, we used compressed air to completely drain the old fluid - and it was ugly - almost jelly like, and bleeding was difficult before, and a breeze after - we have made a decision to do a 24 month fluid drain and replace schedule from now on.