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4 weeks of trying to bleed. Rebuilt master cylinders, calipers, park brakes, replaced as braided lines, and gone thru gallons of fluid. Bleed up and back. Pressure from the caliper nipples (15 psi) back through the system. Also raised the nose and bleed both ways. 

Currently have a vaccum pump running. What next?

Oh it's a single station pedal brakes.

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Welcome aboard Grady...

MS has a few threads on what works...

But it depends a lot on what you have...

The most challenging brake system to bleed is probably any one that has co-pilot brakes...  adding the extra hardware makes it that much more challenging...

 

Speaking of challenging...

You sound quite knowledgable about what you have, and what you have done...

You sound like you are looking for that one missing detail...

How are you going to convey what you are missing?

How is anyone else going to know?

 

Expect many people to try and help...

The more info you deliver up front, the better off you will be...

Got any pics?

Have you rebuilt any of the master cylinders?

Changed out any seals on anything?

Or is this a few decades old?

 

When it comes to bubbles... getting them to move can be done a few ways... can you fly the plane?  In some cases, people have gotten the bubbles to move by using various attitudes and altitudes...

PP thoughts trying to help, not a mechanic...

Best regards,

-a-

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As I said, master cylinders, calipers, parking brakes, were rebuilt. That means all new seals. The 156 stainless braided lines from the master cylinders were replaced. 

(Change of attitude)-The nose was raised 12 inches (nose high) and pressure bled from the from caliper and also from the back to the front.

This work has been completed in the last 4 weeks using several gallons of new fluid. Oh there are no leaks.

Presently running a vaccum pump on the system overnight. 

I'm conveyed all that's been done asking what have I missed?  My test is, will the parking brake hold ac at 2500 rpm. I've talked with other owners and find that most have soft brakes and don't know it.

My background: US Army aviation maintenance officer/test pilot with 33 years service. Mooney owner 26 years. Flying for 55 years....

Thanks for reading and your thoughts.

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Grady,

Thanks for your service!

Thanks for adding the additional details...


I have no idea if my parking brake will hold back 310hp... :)

@2500rpm, it is still 280...

If it fails... 0 to airborne is only seconds away...

 

While we wait for your answers to arrive...

Have you had any luck with the search function?

Best regards,

-a-

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Linings are good, near new.

The pedals are firm and not soft. I sat in a J model and found what solid feels like. What I'm thinking I still have a small amount of air in the system and have tried most of the methods prescribed to remove air. To include removing most panels for visual checks.  Once again I have no leaks.

The master cylinders were both rebuilt and bench tested. Their rod movement is 3/4 of an inch with pressure applied. It all sounds correct, but still has me baffled.  Oh I can hold the ac up to 2400 rpm. It's something little.

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1 hour ago, N231BN said:

If the linings are new have they been burnished?

Are the discs grooved?

If the pedals are solid it's not air.

This^^^^^^^^

I didn’t break my new pads in aggressively enough and they wouldn’t hold during runup no matter how hard I pressed on the pedals. Had to do it again and get them hotter. Procedure is also in Service Manual.

521162289_Screenshot2021-01-11at9_22_18AM.thumb.png.cc9e166574c2dc612d8481004e992f22.png

 

 

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16 hours ago, Grady said:

The pedals are firm and not soft. I sat in a J model and found what solid feels like. What I'm thinking I still have a small amount of air in the system

If the issues isn't from a lack of conditioning the pads, as mentioned above, you may well have some air in the system since you mention yours aren't as firm as another J model you tried. I have dual brakes which are very challenging to get air out and what I finally figu to get the last bit of air out was that I had to remove the cotter pins from the master cylinders so I could lower them and turn them sideways to get fitting on top to bleed them. In their installed position I could not get all the trapped air out. But once I had them hanging from their hoses, still connected, I could twist to get the fittings on top, as well as tap with the handle of screwdriver and push in the piston to free up bubbles all while I had opened the pressure pot to push fluid up from the caliper to the reservoir. A clear line from the junction of the pilot MC's showed the bubbles being freed and moving up as I did all this (tapping and pressing on the piston with my hand without much force). Personally, I found overly aggressive force while bleeding just makes things worse - such as stomping on the brake from the cockpit while fluid was being pushed up.    

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I have a single system. And yes there must be air in the system. 

You cannot move the cylinders when the lines are connected at the ends. That includes turning them sideways. There is no allowance to do that. You cannot switch left and right cylinders. The cylinders were bench tested when rebuilt. They were installed with the cylinders full. 

No bubbles were observed in the lines at the cylinders, parking brake, or calipers.

I've had a vaccum pump running for 22 hours without improvement.

I'll think some more on your thoughts and try bleeding again. Thanks for your insight and findings.

Grady

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Grady,

You have had this plane for decades...

Is this brake challenge caused by the recent overhaul of all the parts you mentioned?

Everything was working well beforehand?

 

Give extra attention to the process described by Kortopates above.

When it comes to minute mechanical details to make things work... Paul comes with all of the proper mechanical background...  and He has done it before...

 

As far as trying to get air out of the system using a vacuum pump for hours...

I’m not sure what to expect from that... the air isn’t dissolved in the brake fluid...  if it exists, it has floated to the top of some area...   the vacuum would allow the bubble to increase in size pretty quickly...   

But, without any motion, the bubble may not move very much...

 

What a super challenging problem this is...

It’s extra memorable...  I remember the first time Kortopates described the effort he went through...

Good luck with your next steps...

PP thoughts only, trying to help out...

Best regards,

-a-

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Planning on playing around with the cylinders tomorrow with an extra set of hands. There isn't much room or play in the area. Crossed fingers. Will report back.

Thanks all.

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On 1/11/2021 at 12:59 PM, kortopates said:

If the issues isn't from a lack of conditioning the pads, as mentioned above, you may well have some air in the system since you mention yours aren't as firm as another J model you tried. I have dual brakes which are very challenging to get air out and what I finally figu to get the last bit of air out was that I had to remove the cotter pins from the master cylinders so I could lower them and turn them sideways to get fitting on top to bleed them. In their installed position I could not get all the trapped air out. But once I had them hanging from their hoses, still connected, I could twist to get the fittings on top, as well as tap with the handle of screwdriver and push in the piston to free up bubbles all while I had opened the pressure pot to push fluid up from the caliper to the reservoir. A clear line from the junction of the pilot MC's showed the bubbles being freed and moving up as I did all this (tapping and pressing on the piston with my hand without much force). Personally, I found overly aggressive force while bleeding just makes things worse - such as stomping on the brake from the cockpit while fluid was being pushed up.    

Well I just spent 35 minutes telling what I had done and had the text lost in space.

A summary

I worked on the LH MC as you detailed. after much tapping and twisting no bubbles were seen. There was 13 PSI brake pressure applied through the caliper.

We next cracked the brake line fitting and had some bubbles pass through the clear line, through the "T" and up the feed line.  More tapping and rotating on the MC.  No more air bubbles. next we put the pins back in and test the 'feel of the pedals'.  I couldn't feel anything different.

Gosh I wish I hadn't loss my first text....When we moved the MC rod there is some free play (3/8ths inch) an then its solid.  When we bench tested the MC, there was no movement and the MC was solid.

I'll try the same with the RH MC tomorrow. I have brakes, but what is the correct amount of stop?  I pushed against the AC with the brakes applied and it doesn't move. period.  I set the parking brake and pushed the plane.  That's not right. 

Thanks for getting me going in the right direction.

Grady

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45 minutes ago, Grady said:

Well I just spent 35 minutes telling what I had done and had the text lost in space.

A summary

I worked on the LH MC as you detailed. after much tapping and twisting no bubbles were seen. There was 13 PSI brake pressure applied through the caliper.

We next cracked the brake line fitting and had some bubbles pass through the clear line, through the "T" and up the feed line.  More tapping and rotating on the MC.  No more air bubbles. next we put the pins back in and test the 'feel of the pedals'.  I couldn't feel anything different.

Gosh I wish I hadn't loss my first text....When we moved the MC rod there is some free play (3/8ths inch) an then its solid.  When we bench tested the MC, there was no movement and the MC was solid.

I'll try the same with the RH MC tomorrow. I have brakes, but what is the correct amount of stop?  I pushed against the AC with the brakes applied and it doesn't move. period.  I set the parking brake and pushed the plane.  That's not right. 

Thanks for getting me going in the right direction.

Grady

Glad you got some air out cracking the lines, but I suspect there is still some left in the MC. In addition to taping with the fittings on top, also move the MC rod while in the rotated position and that may also free some bubbles up. You'll only be able to push it in by hand maybe 1/8" - I don't recall anywhere near 3/8" unless there was a lot of air. The amount of freeplay you have the when the MC are in position and pressing from the brake pedals varies with the MC model. The original ones used in the K were very tight. The newer larger capacity ones being used have more freeplay.

"I pushed against the AC with the brakes applied and it doesn't move. period.  I set the parking brake and pushed the plane.  That's not right. "

That really sounds like the parking brake lever was pulled without pressing firmly on the brakes. Which would not lock the brakes up. Recall the parking brake just holds the brakes in the position of the applied pedal force. If that was done properly, and the parking brake is not holding the applied pressure, then you'll have to replace the 4 o-rings in the parking brake (4 is from memory).

Good luck!

 

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13 minutes ago, kortopates said:

Glad you got some air out cracking the lines, but I suspect there is still some left in the MC. In addition to taping with the fittings on top, also move the MC rod while in the rotated position and that may also free some bubbles up. You'll only be able to push it in by hand maybe 1/8" - I don't recall anywhere near 3/8" unless there was a lot of air. The amount of freeplay you have the when the MC are in position and pressing from the brake pedals varies with the MC model. The original ones used in the K were very tight. The newer larger capacity ones being used have more freeplay.

"I pushed against the AC with the brakes applied and it doesn't move. period.  I set the parking brake and pushed the plane.  That's not right. "

That really sounds like the parking brake lever was pulled without pressing firmly on the brakes. Which would not lock the brakes up. Recall the parking brake just holds the brakes in the position of the applied pedal force. If that was done properly, and the parking brake is not holding the applied pressure, then you'll have to replace the 4 o-rings in the parking brake (4 is from memory).

Good luck!

 

All seals and O rings were replaced on the MC, parking brake, and calipers. (Earlier text)

MC rod was turned and pressed per your suggestion. MC was turned sideways and tapped.

I think you can compress the internal MC spring more than 1/8th inch, at least on this one was 3/8s inch.

How much brake fluid  pressure should i push in the system? This is the pressure side of the brake system. 

Thank you again

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Very good, I can't say on the pressure in PSI. I use one of these from ATS https://aircraft-tool.com/shop/detail.aspx?id=225DX&AspxAutoDetectCookieSupport=1

I just pump it up till the pressure is pretty firm (20-40 pumps) and then connect it to the caliper. When I am ready to bleed I open the bleeder port on the caliper and then roll on up to the MC's on the creeper to rotate, tap and work the rod etc. (doing this as a one man operation).  But it fills a pint catch container I have connected to the reservoir within about 3 minutes. The actual PSI I don't know, but I wouldn't think very much. You're earlier mention of 15 psi sounds reasonable if its pushing fluid through it pretty quickly.

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Lost typing...

Doesn’t happen very much anymore...

But when it does...  it is highly likely to still be in the system...

Click in the blank box like you are ready to type again... if it is there, it magically reappears...

Including when the iPad runs out electricity after two warnings... 10 minutes left, five minutes left... :) 

Best regards,

-a-

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Grady,

Checking your procedure for setting the parking brake...

Paul had mentioned it above...

It is one of those things that gets ‘forgotten’ over time... it doesn’t work like any car I have ever owned... :)

Best regards,

-a-

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On 1/13/2021 at 10:15 PM, kortopates said:

Glad you got some air out cracking the lines, but I suspect there is still some left in the MC. In addition to taping with the fittings on top, also move the MC rod while in the rotated position and that may also free some bubbles up. You'll only be able to push it in by hand maybe 1/8" - I don't recall anywhere near 3/8" unless there was a lot of air. The amount of freeplay you have the when the MC are in position and pressing from the brake pedals varies with the MC model. The original ones used in the K were very tight. The newer larger capacity ones being used have more freeplay.

"I pushed against the AC with the brakes applied and it doesn't move. period.  I set the parking brake and pushed the plane.  That's not right. "

That really sounds like the parking brake lever was pulled without pressing firmly on the brakes. Which would not lock the brakes up. Recall the parking brake just holds the brakes in the position of the applied pedal force. If that was done properly, and the parking brake is not holding the applied pressure, then you'll have to replace the 4 o-rings in the parking brake (4 is from memory).

Good luck!

 

On 1/13/2021 at 11:01 PM, kortopates said:

Very good, I can't say on the pressure in PSI. I use one of these from ATS https://aircraft-tool.com/shop/detail.aspx?id=225DX&AspxAutoDetectCookieSupport=1

I just pump it up till the pressure is pretty firm (20-40 pumps) and then connect it to the caliper. When I am ready to bleed I open the bleeder port on the caliper and then roll on up to the MC's on the creeper to rotate, tap and work the rod etc. (doing this as a one man operation).  But it fills a pint catch container I have connected to the reservoir within about 3 minutes. The actual PSI I don't know, but I wouldn't think very much. You're earlier mention of 15 psi sounds reasonable if its pushing fluid through it pretty quickly.

Got back to the ac today. After knocking the 2 bubbles out of the right MC yesterday and moving the rod, we turned our attention to the parking brake rigging. As I've said ALL calipers, MCs, parking brake, and braided lines were replaced.

We checked the parking brake rigging and made adjustments. Turned out we didn't get full travel of the arm.  we moved the module. THat little adjustment allowed more travel of the arm AND working parking brake.

At 2600 RPM the brake held the AC....no movement. Proving also the pedal brakes now hold at 2700 rpm..  So problems solved.

That trick  of removing the MC pins, twisting the rod while tapping the cylinder isn't written in the service manual, but should be. Guys you may want to print this and place it in your books.

I think most people don't get this involved with the ac. I like a challenge and this one was challenging and called for going outside of the box.  I want thank those offered their thoughts and suggestions.   So if you have soft pedals or your parking brake won't hold your ac at high RPM, you have a problem.

Grady M20K

 

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Great details shared, Grady!

:)

Don’t be surprised when people send you a message asking for this sliver of important advice you just outlined...

Thanks for taking the time to document all those details...

I put a link on Mooney.com   In the maintenance forum....

Have a look... https://www.mooney.com/forums/topic/mooney-brake-bleeding-procedure-additional-details-to-be-considered/

The Mooney factory site is a new and growing method of communicating with the factory...   I’m still trying to figure it out...

Best regards,

-a-

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