More Brake Issues

[AZOutlaw]

I think I've read every brake thread, worked on mine a lot, and still can't hold in place during a run up.  Here's where I'm at.  Bled the brakes the old school/pickup truck method with someone pumping and opening and closing the bleed drains.  This was a great first step as we got some gunk out of the bottom and didn't push it back through the system.  We then noticed a leak on the flap pump and the parking brake valve.  Took the flap pump apart and replaced o-rings and did the same with the brake valve.  Filled up the reservoir and then started pumping fluid in from the bottom.  Pumped some out the "T" by the flap cylinder.  I now have great flap movement and no leaks but still can't get the brakes good.  We connected a barbed fitting and a long piece of tubing to the top vent hole on the reservoir and ran that into a container on the floor.  I could pump from either brake and fill that line with fluid.  But here's the strange part. About 15 seconds after stopping the pump and closing the bleeder, air bubbles would start coming out the top of the reservoir into the line.  Any idea where this Air would come from?  I think it's a sealed up system.  The last thing I noticed......the park brake won't hold the plane at even 1000-1200 rpm but with the park brake engaged, my pedal brakes are much stronger.  Any ideas?

I'm thinking of rebuilding master cylinders next but the brakes don't seem to leak down and feel solid on the pedals. 

[N601RX]

I think much of the problem comes from the cylinders being horizontal and the outlets on the side. This allows air to get trapped in the upper part of the cylinder. I replaced my original paramount cylinders with the newer style Cleveland cylinders. These have a extra passageway machined in the end to help get the air out. I used a $8 pump up sprayer from lowes garden dept filled with fluid to bleed mine. That was the basis of my suggestion to go ahead and replace all the seals and any questionable hoses in the system at once and be done with it rather that do them one at a time every 6 months.

[duke]

you have air in the system. park is simply a line lock, and when engauged simply closes the brake line and holds pressure on brake piston. Have someone pump brake while bleeding from bottom, this works for me. By the way, do you have brakes on copilot side? If so bleeding ca be a real PIA.

[Andy95W]

Simple test for air in your brakes: pump the brakes 2-3 times. If the pressure increases, you've got air. If not, you've got more troubleshooting to do.

If one brake is significantly more powerful than the other, you will need to replace the o-rings in your master cylinder(s).

I had the same issue with my M20C. I rebuilt my brake cylinders, calipers, and parking brake valve. Nothing. I replaced my pads. Still nothing. I put a pair of calipers to my discs and found they were significantly thinner than spec.

Turns out, Mooney changed the brakes sometime between 1964 and 1967. If your brake pads have three rivets, yours are the earlier ones. If 2 rivets, the later (thinner) ones.

You can't just look at the Aircraft Spruce Catalog, it can lead you down the wrong path.

Long story short: bought the right discs, brakes are 100% now.

BTW, my parking brake still doesn't hold well, and I'm okay with not using it.

[RobertGary1]

I've hear that you don't want to pressure bleed them but to vacuum bleed them. I've actually never bled a mooney system so I can't swear to it myself.

[cliffy]

Lets start at the beginning-

When you press both brakes are they both hard and near the top of the pedal push?

Does either one of them slowly bleed down as you keep pressure on?

Is either one of them soft and spongy?

The reservoir is not a "closed" system. It has air at the top and with the can on the ground fluid will drain back out of the line bringing air with it.

Have the wheel cylinders ever been opened, cleaned and new orings installed?

How old are your flexible brake hoses at the wheels?

How old are your brake pads?

What condition is your brake disc in? Is it too thin from wear?

When you bleed the brakes do you have any air coming out with the fluid?

All these have a bearing on how well the brakes work.

More information is needed to help you.

[AZOutlaw]

Just wanted to answer a few questions and provide an update. 

No, I do not have co-pilot brakes.  Good for bleeding but potentially bad for my passengers and the aircraft should I pass out.

 

The brake pedals seem good.  Firm, near the top, don't bleed down when held. 

Not sure on the cylinders or hoses but they do not leak. 

Discs, or rotors, seem good and smooth.

Brake Pads....well this is one of my problems.  I was told by two people that they looked fine including during my annual.  I finally got frustrated enough and pulled them off myself.  They are shot.  I just started polishing the tops of the rivets but can't see or feel any grooves in the rotors.  I think I caught that just in time and will probably solve the problem. 

Air in the system.....this one I can't figure out.  I believe it is a closed system the way I have it plumbed to bleed.  I realize there is air, and a vent, at the top of the reservoir, but this is where I'm pushing fluid out of the system.  I can push a solid stream of fluid all day long, but as soon as I stop, air bubbles show up as seen in the picture attached.  I have no leaks anywhere and I would think if air can get in, fluid must be able to get out.  I can only assume that the siphon created by this hose going all the way to the floor is pulling a little air through an O-ring or fitting.  Make sense to anyone else?  My hope is the new pads will fix all and I'll keep a lookout for leaks and check fluid regularly.

Thanks All!

[N601RX]

Which master cylinders do you have?  Is it the original paramount which are black steel or the newer Gerdes/Cleveland which are aluminum? The newer ones are easier to bleed.  Its likely the air is getting trapped in the upper half of the master cylinder.  It will help greatly if someone sets in the plane and pumps the pedals slowly while the other person pushes fluid up through the system.  Are you using some type of pressure pot to push the fluid?

[AZOutlaw]

I have the old paramount master cylinders and yes on the pressure pot.  I noticed that when I go at a slow steady pace I'll get 2 -1/2" air bubbles about every 12" of fluid.  Now that my calipers are off and dangling waiting for new pads, I did find a leak in one of the hose fittings.  This could surely let air in. 
Now to order hoses and wait for UPS to carry on.

[Tmack1]

I just had mine looked at because I would see a small wet spot on the caliper every once in a while and they said I needed new line since they have no been replaced for about 12 years and when they took every thing apart I had 2 lovely cracked calipers that were the cause of the wet spot this trip to the shop for an engine monitor just keeps getting more expensive lol

[cliffy]

AZOutlaw When was the last time your wheel calipers were apart cleaned and new orings?Cgeck your log book. If it has never been done now is the time. Not difficult not expensive, Do you have the tools to rerivitthe brake pads on or will you A&P be doing it?

[N601RX]

I just had mine looked at because I would see a small wet spot on the caliper every once in a while and they said I needed new line since they have no been replaced for about 12 years and when they took every thing apart I had 2 lovely cracked calipers that were the cause of the wet spot this trip to the shop for an engine monitor just keeps getting more expensive lol

The entire calipar assembly is very expensive. If I remember correctly around $700 each. I found you could buy just the new housing and then use the other parts off the old one to build up a good calipar for a little over $200 each.

[Tmack1]

Ya I got new housings for 250 each and new rotors new lines and 11 new lord mounts for the gear since he called me back and said they need replaced also never ending but it will be nice when it's done and I hope no more phone calls from the shop lol

[Tmack1]

I don't think anything has really been replaced in about 20 years I just taking care of someone else's neglect The Lord mount are original from what I can see in the log books

[AZOutlaw]

Cliffy, they were done a few years back when it had a very extensive annual. I took one apart yesterday when I found the leaky hose fitting. It looked great. I did order new O rings since I need to remove the hose, I might as well replace those 75 cent parts too. My A&P stopped by yesterday with his rivet tool so all good there. I've been working with him but he just hasn't been available a lot. He witnessed the air in the system issue and said he would be back to help when I got the new hoses.

[cliffy]

That sounds good.When I had mine apart the first time they hadn't been apart in 30 years. It was nothing but red jelly inside. Bet you have good brakes when you're done.

[AZOutlaw]

I now have great brakes and even a strong parking brake.  It was a lot of headaches, maybe a few choice words, but I did contain all tool throwing.  I believe we finally tracked it down to the brake lines just above the calipers.  There's a 36" flexible piece here and we think it was letting a small amount of air in as we pumped fluid up from the bottom.  I just kept pumping, but it was pulling air with it.  They never did leak fluid until we removed the calipers and they were dangling by the hose.  The lines we took off were old and crusty.  I don't know if they were the originals on a '65 but I guess they could have been.  Thought they had been replaced not long ago,  Learned a lot about the whole system so it's all good.  Had a flap pump issue too (in another thread) and flaps are great now as well.    A few more parts and repairs and it'll be an Ovation.

Thanks to all for the tips and information!!

[carusoam]

"A few more parts and repairs and it'll be an Ovation." -AZO

Same damned thing happened to me...

Took 10 years or so.

[Yetti]

Would the collective wisdom happen to know the I.D. of the 303/stratoflex line that is used in the wheel well to the caliper?

[AZOutlaw]

I believe the line is called a -4 size which is 1/4" ID and 1/2" OD.

[scottfromiowa]

I now have great brakes and even a strong parking brake.  It was a lot of headaches, maybe a few choice words, but I did contain all tool throwing.  I believe we finally tracked it down to the brake lines just above the calipers.  There's a 36" flexible piece here and we think it was letting a small amount of air in as we pumped fluid up from the bottom.  I just kept pumping, but it was pulling air with it.  They never did leak fluid until we removed the calipers and they were dangling by the hose.  The lines we took off were old and crusty.  I don't know if they were the originals on a '65 but I guess they could have been.  Thought they had been replaced not long ago,  Learned a lot about the whole system so it's all good.  Had a flap pump issue too (in another thread) and flaps are great now as well.    A few more parts and repairs and it'll be an Ovation.

Thanks to all for the tips and information!!

I lived all of this...

Nice to have great brakes and flaps isn't it?

44 years was long enough for those parts...