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Is M20C brake bleeding possible?


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I had to reseal my master cylinders and noticed the in/out fittings are in the side of each cyl. (Horizontal position when mounted in airframe) To make problems worse is the inlet port is a 1/16” orifice further lowering the escape port during bottom up bleeding. Hard lines also prevent manipulation of each cyl. for allowing air to rise. 
  so far haven’t attempted anything but just wondering what kind of treat I’m in for. Is pre bleeding cylinders and plugging ports with mineral grease a “thing” or futile attempt?

 

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You gotta bleed them by injecting fluid at the bottom with an overflow reservoir attached to top of brake fluid reservoir.   There are several detailed discussions here on MS.  Getting air out of horizontal cylinders is a trick also described here.   Search using google:   bleeding brakes site:mooneyspace.com

 

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I've even heard of people tying the tail to the ground to try to encourage the bubbles to go to the front of the cylinders, or tapping on the cylinders during bleeding to break them loose.   I usually have to combine bottom-up and top-down bleeding to get it completely done, but I've seen more big bubbles come out during bottom-up.   That's on my J model, but they're all similar.

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My J is the same, with orifices on the side of the cylinders, and I had heard stories so I worried.

But I had no problems at all, the reason why I feel pretty sure is because my bleeder looks like an insect sprayer and you pressurize it with a pump, attach it to the bleeder nipple at the bottom of the slave cyl and open the valve, then you get a steady flow of fluid, it’s the steady flow that I believe does the trick, if you do the oil can route you get squirts of fluid, start, stop and I believe a constant flow flushes out the bubbles better.

https://www.aircraftspruce.com/catalog/lgpages/hydraulicBleedertank.php

I drained the tank in the back, then bled the left brake until the tank overflowed, disconnected the bleeder and moved to the right brake, drained the tank and bled until it overflowed again, sucked fluid out until it was at the right level and have had perfect not soft brakes since.

I think flushing the system ever so often if you use 5606 is important as that stuff given enough time turns into a gel.

If you use 83282 then that’s not an issue, plus it’s fire resistant.

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1 hour ago, A64Pilot said:

My J is the same, with orifices on the side of the cylinders, and I had heard stories so I worried.

But I had no problems at all, the reason why I feel pretty sure is because my bleeder looks like an insect sprayer and you pressurize it with a pump, attach it to the bleeder nipple at the bottom of the slave cyl and open the valve, then you get a steady flow of fluid, it’s the steady flow that I believe does the trick, if you do the oil can route you get squirts of fluid, start, stop and I believe a constant flow flushes out the bubbles better.

https://www.aircraftspruce.com/catalog/lgpages/hydraulicBleedertank.php

I drained the tank in the back, then bled the left brake until the tank overflowed, disconnected the bleeder and moved to the right brake, drained the tank and bled until it overflowed again, sucked fluid out until it was at the right level and have had perfect not soft brakes since.

I think flushing the system ever so often if you use 5606 is important as that stuff given enough time turns into a gel.

If you use 83282 then that’s not an issue, plus it’s fire resistant.

 Did you start with empty masters? I would feel better if you did with no bleeding issues. I might be a little ocd.
  I understand pressure bleeding but fail to see how fluid can possibly return through the masters with enough turbulence to mix air from upper areas of a horizontal cylinder and exit through the inlet orifice located at 3 o’clock. Even tilted nose up 45deg. It would require a 90deg. Roll each way and that still wouldn’t remove all air from the delivery side of the master piston through the piston center valve. 
 I guess sometimes I have to except things as good enough until they’re not. 
 Everything I read about about this is how long it took but somehow it worked out in the end without knowing the reason why. 

 

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Like @A64Pilot mentioned above, the trick is to push enough fluid through (with out stopping) from the bottom (caliper). I've done mine several times and never had an issue

side note: I use an oiler (shown below), and clear tubing between the oiler and caliper so I can make sure I'm not pumping air into the system, I also use clear tubing (4 foot or so) from the reservoir to a catch can on the hangar floor, laying under the plane you can watch for the air bubbles to stop showing in the tube going to your catch can, a few more pumps and close off the bleeder...keep the fluid moving up and out until no more bubbles

image.png.4cb56e3ee9d146e8279a1510b24ed91e.png

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2 hours ago, Kelpro999 said:

 Did you start with empty masters? I would feel better if you did with no bleeding issues. I might be a little ocd.
  I understand pressure bleeding but fail to see how fluid can possibly return through the masters with enough turbulence to mix air from upper areas of a horizontal cylinder and exit through the inlet orifice located at 3 o’clock. Even tilted nose up 45deg. It would require a 90deg. Roll each way and that still wouldn’t remove all air from the delivery side of the master piston through the piston center valve. 
 I guess sometimes I have to except things as good enough until they’re not. 
 Everything I read about about this is how long it took but somehow it worked out in the end without knowing the reason why. 

 

Obviously it can be done, but you’re prudent to be cautious and think it through.  The only time I’ve broken down on the road was a master cylinder leak.  I found a mechanic on the field who had the proper O rings on hand and rebuilt the brakes the next morning.  I had soft/squishy/50% effective left brakes until my home mechanic spent an hour with the plane tilted back working on it.  It was fine after that.  So clearly it can be done ok, but, yes, it can be a pain if you’re in a rush.

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On 11/24/2022 at 7:05 PM, Kelpro999 said:

 Did you start with empty masters? I would feel better if you did with no bleeding issues. I might be a little ocd.
  I understand pressure bleeding but fail to see how fluid can possibly return through the masters with enough turbulence to mix air from upper areas of a horizontal cylinder and exit through the inlet orifice located at 3 o’clock. Even tilted nose up 45deg. It would require a 90deg. Roll each way and that still wouldn’t remove all air from the delivery side of the master piston through the piston center valve. 
 I guess sometimes I have to except things as good enough until they’re not. 
 Everything I read about about this is how long it took but somehow it worked out in the end without knowing the reason why. 

 

Yes empty as in dry, I had replaced the O-rings and Statoseal, had them both off, of course when you remove them the tank drains.

It worked, no mushy pedal at all, either side, maybe I just got lucky, but don’t believe it, depending on how much you pump the pump on my bleeder the higher the pressure, no way could you get the volume or pressure from an oil can that the bleeder ball can deliver.

You could build your own of course from an insect sprayer but I suspect the pump seals and maybe even the tank wouldn’t last long, 5606 eats up some types of plastic and rubber.

I’ve seen one built from an old propane tank, use shop air to build the pressure, 10 PSI is plenty. I just bought one though, an empty refrigerant tank would make a nice one.

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12 hours ago, A64Pilot said:

Yes empty as in dry, I had replaced the O-rings and Statoseal, had them both off, of course when you remove them the tank drains.

It worked, no mushy pedal at all, either side, maybe I just got lucky, but don’t believe it, depending on how much you pump the pump on my bleeder the higher the pressure, no way could you get the volume or pressure from an oil can that the bleeder ball can deliver.

You could build your own of course from an insect sprayer but I suspect the pump seals and maybe even the tank wouldn’t last long, 5606 eats up some types of plastic and rubber.

I’ve seen one built from an old propane tank, use shop air to build the pressure, 10 PSI is plenty. I just bought one though, an empty refrigerant tank would make a nice one.

 Construction of a pressure pot won’t be a problem but I’m beginning to wonder if 100% air free is desirable since it appears impossible given master cylinder design, installed configuration and current bleeding procedures. ? Perhaps this “trapped air” helps with brake modulation and park brake function.?. I may try both ways when my ocpd and hoarder supplies collide. I still have other hoses to replace and components to rebuild before returning to this issue.  
I very much appreciate your input on this matter 
  

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15 minutes ago, Kelpro999 said:

 Construction of a pressure pot won’t be a problem but I’m beginning to wonder if 100% air free is desirable since it appears impossible given master cylinder design, installed configuration and current bleeding procedures. ? Perhaps this “trapped air” helps with brake modulation and park brake function.?. I may try both ways when my ocpd and hoarder supplies collide. I still have other hoses to replace and components to rebuild before returning to this issue.  
I very much appreciate your input on this matter 
  

Some folks believe that after bleeding the brakes, if you pump the brakes while doing some  steep climbing turns, you can get the air out of the Master cyl.

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2 hours ago, 0TreeLemur said:

Some folks believe that after bleeding the brakes, if you pump the brakes while doing some  steep climbing turns, you can get the air out of the Master cyl.

Hammerhead comes to mind 

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2 hours ago, Kelpro999 said:

 Construction of a pressure pot won’t be a problem but I’m beginning to wonder if 100% air free is desirable since it appears impossible given master cylinder design, installed configuration and current bleeding procedures. ? Perhaps this “trapped air” helps with brake modulation and park brake function.?. I may try both ways when my ocpd and hoarder supplies collide. I still have other hoses to replace and components to rebuild before returning to this issue.  
I very much appreciate your input on this matter 
  

Air in the brake line is never desirable.   The hydraulic fluid won't transmit full pressure to the brake caliper until all of the bubbles are compressed, which may just delay application of the brakes or in bad cases means you have to pump the brake pedal multiple times before you'll get braking action.   

While the orientation of the brake master cylinders does make it a little trickier to bleed than some systems, they're not impossible and they won't work properly with air in them.

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I’m sure that when Mooney built these planes, they got them bled.  It’s a matter finding and expelling the last of the air bubbles.  I’ve found that in many cases the air is at the top of the main wheel wells, where conveniently Mooney put a union between the metal line in the wing and the flex hose to the gear.  You can expel air here.

To prove which half of the system contains air, take the line off the pressure side of the master cylinder and install a line cap.  Now pump up the brakes via the pedal and crack the cap loose to expel any air, when it’s solid you know the master cylinder has no air.  Quickly remove the line cap, and reinstall the line, open the union in the wheel well and pump the pedal until fluid comes out at the union, pump fluid up from the wheel cylinder to the union, when there is no more air secure the union.

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 MS is the greatest resource anyone could wish for. I  appreciate everyone here when working through problems or just late night reading. 
  This topic is  an attempt to head off imaginary problems headed my way during this project. While I haven’t yet filled, bled and tested this system it may very well have no issues at all (Fingers crossed). It’s also very hard to believe mounting a “vertical brake cylinder” with a reduced inlet orifice horizontally as an oversight and not by design allowing some trapped air for modulation purposes. I kind of believe nose up bleeding will “firm” the pedal and nose down bleeding will soften the pedal. (From an air bound starting point)
This is going to be interesting

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13 hours ago, M20Doc said:

I’m sure that when Mooney built these planes, they got them bled.  It’s a matter finding and expelling the last of the air bubbles.  I’ve found that in many cases the air is at the top of the main wheel wells, where conveniently Mooney put a union between the metal line in the wing and the flex hose to the gear.  You can expel air here.

To prove which half of the system contains air, take the line off the pressure side of the master cylinder and install a line cap.  Now pump up the brakes via the pedal and crack the cap loose to expel any air, when it’s solid you know the master cylinder has no air.  Quickly remove the line cap, and reinstall the line, open the union in the wheel well and pump the pedal until fluid comes out at the union, pump fluid up from the wheel cylinder to the union, when there is no more air secure the union.

I’ve used that union after caliper reseal and it worked perfectly. I’ll be doing some bleeding as you suggest along with some unrealistic bench bleeding for comparison. I think I might be going a little overboard with this not yet a problem I have going on.
 Thank you for your input!

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First suction bleed down to purge the jelly old fluid. Don’t push that into the master cylinders. Then bleed up with a pressure bleeder to purge air. In my experience you won’t get it all. Then pull into a 20 degree pitch up and pump the brake peddles. Maybe a couple times. Then you’ll get the air out. 

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35 minutes ago, RobertGary1 said:

First suction bleed down to purge the jelly old fluid. Don’t push that into the master cylinders. Then bleed up with a pressure bleeder to purge air. In my experience you won’t get it all. Then pull into a 20 degree pitch up and pump the brake peddles. Maybe a couple times. Then you’ll get the air out. 

There’s quite a bit of gooey mess in all hyd. Valves and lines. After replacing all soft lines I’ll circulate fluid end to end with master cyl. bypass lines in place. That should dissolve most of it. I’ll try “pitch up” during bleed testing and report findings. Thanks for input 

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Oiler, clear hose from the lowest point or caliper works every time. Just make sure your clear hose stays on the bleed port and have another clear hose off the reservoir to clean container. You or somebody helping you can see the air come out. It's a bit hard sometimes on your hand.     

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If you dont want to spend three days , pump up the brakes with the pedals , and crack the lines where the flex line , meets the hard line , in the wheel well , It is the highest point in the system , there is this new thing called "Gravity" ... It will gravity bleed out at that fitting , you will see bubbles come out with the fluid , when you stop seeing bubbles , tighten the lines , and see if you have a pedal , if not , let it sit for a few minutes , and crack the line again ,  They will bleed , unless the fluid is so old , it has solidified.... The air wil always collect , at the highest point in the system...   Tilting up the plane does nothing... 

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RobertGary1 has the correct procedure especially if you have not bled the brakes in a while. A couple of years ago LASAR had a special on the STC that allows you to swap the calipers to the front to get them out of the airstream when the gear is up. When I took the calipers apart they were full of 5606 jelly. After I cleaned them up and swapped them over, I then bled them from the caliper to the reservoir. Worked great, no air.2075D4A5-9DAD-48ED-BD43-998FFFEF87B2.jpeg.f9a45d8fe5207246d2e9b47519f12f20.jpeg

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33 minutes ago, Alan Fox said:

If you dont want to spend three days , pump up the brakes with the pedals , and crack the lines where the flex line , meets the hard line , in the wheel well , It is the highest point in the system , there is this new thing called "Gravity" ... It will gravity bleed out at that fitting , you will see bubbles come out with the fluid , when you stop seeing bubbles , tighten the lines , and see if you have a pedal , if not , let it sit for a few minutes , and crack the line again ,  They will bleed , unless the fluid is so old , it has solidified.... The air wil always collect , at the highest point in the system...   Tilting up the plane does nothing... 

  At this time the masters are still out of chassis yet to be installed. The low pressure side of the system including flaps are filled with Tar. I don’t think any of it has ever been flushed. That’s 60 yrs. But I’ve added too the reservoir and was able to bleed at the wheel well fitting after a caliper reseal. I get that “tilting” the masters will only slightly alter the trapped air volume but I’m curious to feel the difference if at all. I expect to reseal the park and flap valves after the tar is dissolved. Good deeds never go unpunished.

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1 hour ago, 65MooneyPilot said:

RobertGary1 has the correct procedure especially if you have not bled the brakes in a while. A couple of years ago LASAR had a special on the STC that allows you to swap the calipers to the front to get them out of the airstream when the gear is up. When I took the calipers apart they were full of 5606 jelly. After I cleaned them up and swapped them over, I then bled them from the caliper to the reservoir. Worked great, no air.2075D4A5-9DAD-48ED-BD43-998FFFEF87B2.jpeg.f9a45d8fe5207246d2e9b47519f12f20.jpeg

Yea, when I first resealed one cylinder it seamed like it was working with low viscosity wet grease. I’ll check and consider the STC. Thanks

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