**Solved: Can't bleed brakes from bottom up

[Skates97]

During annual we found the right brake master cylinder was leaking some and my AP/IA wanted it resealed. We got the o-rings for it and I took it apart, replaced the o-rings, put it all back together and back in the plane and then tried to bleed the brakes from the bottom up. However, I can't get fluid to go up and through the master. With the bleeder loosened and the pot not hooked up if you pump the brake it squirts fluid out each time. Hook the pot up and try to send fluid back up through and no luck.

Thinking I'm missing something I had my AP/IA get the plane from the hangar yesterday to have him bleed the brakes, he said the same thing, he can't get fluid back through the master from the bottom and thinks I must have gotten something wrong when I was putting it back together. He can pull it off the plane to take it apart and look at it, but probably not until next week. Ideas from anyone that has run into this before? I may go by today and remove it for him and take it over to his hangar to have him look at it.

[JimB]

I'm sure you checked it but the parking brake isn't on/closed right? There really isn't much to get "wrong" with the o-rings that would prevent fluid flow.

Edited January 29, 2021 by JimB

[Skates97]

Yes, parking brake is off. The master is pretty simple and I had everything laid out on the table along with the schematic so pretty sure it all went back together the same way it came apart. Plus it pumps fluid out, just can't bleed from the bottom up. 

He just did brakes during an annual on another Mooney and bled the brakes on it from the bottom but couldn't get mine to take fluid. 

[JimB]

20 minutes ago, Skates97 said:

Yes, parking brake is off. The master is pretty simple and I had everything laid out on the table along with the schematic so pretty sure it all went back together the same way it came apart. Plus it pumps fluid out, just can't bleed from the bottom up. 

He just did brakes during an annual on another Mooney and bled the brakes on it from the bottom but couldn't get mine to take fluid. 

Weird. I'll be interested to know what you find. 

[Phil Thomas]

Have you made sure that the pedal on that master cylinder isn't pressed in at all? I've had issues on other planes where the pedal was binding and slightly depressed causing fluid to not be able to flow back when bleeding from the bottom.

[Skates97]

37 minutes ago, Phil Thomas said:

Have you made sure that the pedal on that master cylinder isn't pressed in at all? I've had issues on other planes where the pedal was binding and slightly depressed causing fluid to not be able to flow back when bleeding from the bottom.

Thanks, something to check on.

[EricJ]

I hesitate to mention it because it is a low probability event, but sometimes old flexible hoses collapse or clog up internally.   If they're old, it may be worth looking at.

Otherwise, do you have a mighty-vac or something (an assistant?) to try bleeding top down?

[Skates97]

53 minutes ago, EricJ said:

I hesitate to mention it because it is a low probability event, but sometimes old flexible hoses collapse or clog up internally.   If they're old, it may be worth looking at.

Otherwise, do you have a mighty-vac or something (an assistant?) to try bleeding top down?

Hoses aren't exactly new but look to be in good shape. I think they were replaced within the last ten years by the prior owner but would need to take a look at the logs.

[Bolter]

If you crack the line at the master, you can see if you can flow that far.  Then progressively tighten and loosen fittings until you find what is blocking your flow.  Maybe old debris acting like a check valve.  Maybe flush lots of clean fluid top-down, so you have cleared the lines before filling bottom-up.  

When I was chasing air leaks in my brakes, hoses that looked good turned out to have little flaws.  I replaced 2 during the process.  

Just remember brakes are not required for flight :-) 

[47U]

Does you have the dual brakes?  Could the shuttle valve be preventing flow?

[MooneyMitch]

1 hour ago, 47U said:

Does you have the dual brakes?  Could the shuttle valve be preventing flow?

I learned about shuttle valves during my last fluid replacement.   

One of my valves had a damaged O ring and would not allow complete bleeding. Wound up pulling remaining hair from my already thinned head of hair over this.....

However, the shuttle valves did not prevent fluid from being introduced at the calipers.

A blockage of some sort me thinks for Richard.

Looking forward to the finish line with this mystery..... luv MooneySpace!! 

[Skates97]

2 hours ago, Bolter said:

If you crack the line at the master, you can see if you can flow that far.  Then progressively tighten and loosen fittings until you find what is blocking your flow.  Maybe old debris acting like a check valve.  Maybe flush lots of clean fluid top-down, so you have cleared the lines before filling bottom-up.  

When I was chasing air leaks in my brakes, hoses that looked good turned out to have little flaws.  I replaced 2 during the process.  

Just remember brakes are not required for flight :-) 

Nope, but they tend to come in handy on the ground. 

1 hour ago, 47U said:

Does you have the dual brakes?  Could the shuttle valve be preventing flow?

 

Nope, just pilot side.

[Hank]

2 hours ago, Bolter said:

Just remember brakes are not required for flight :-) 

They sure are handy for stopping at the end of flight. Even better is having functional brakes on TWO wheels! Just slowly, slowly refilled mine on the right side, as it had nothing while the left brake worked. That landing to meet my IA was interesting . . . .

So check your master cylinder. Mine was so low I could barely see fluid with a flashlight under the panel. 

[carusoam]

We have a new brake expert around here...

Started a thread similar to this,  couple of weeks go....

Only, it was specific to M20Ks...

See if @Grady is stopping by the neighborhood...

Best regards,

-a-

[Skates97]

Solved

I took off a few hours early from work and headed over to the airport stopping by my AP/IA's hangar to borrow his little hand pump pot. The system was working fine before I rebuilt the master cylinder and since the only thing I touched in the system was the master cylinder it made sense that somewhere in there was the problem. I removed it and given the fact that the fluid from the reservoir side was draining out until I put a plug in the line there was no blockage there. I hooked up the pot at the caliper and gave it a couple of pumps and the fluid ran out of the end of the line where it hooks up to the master cylinder, no blockage there.

I removed the snap-ring and pulled the shaft out. Everything looked like it was in the right place and in the right order. There's a cotter pin that goes through 89 and also the end of 86. I removed the cotter pin to remove 86 and when I did found that I didn't have oring #87 seated all the way in 86. There is a little groove in 86 that it is supposed to be all the way down in. Because it wasn't seated all the way it was actually sealing the gap between 86 and 83 and not letting any fluid pass back through. I got 87 seated all the way in, reassembled, and put it back in the plane.

Hooked up the pot at the caliper and it easily pumped fluid back up through this time. A few pumps at a time and then checking the level in the reservoir, a few pumps, check level, once it had raised the level almost all the way I snugged the bleeder needle back down, and removed the line to the pot. Checked the brakes, not mushy but good and firm. Pulled the plane out, started it up, brakes held fine. After letting the engine warm up ran it up to 2,200 rpm and brakes still held fine. All is well.

[MooneyMitch]

Good job Richard!  Congratulations and I think I should win the thread prize !! 

It’s sooooo great when your airplane is all happy again!! 

[RLCarter]

I’d bet good money you had it correct the 1st time but rolled out during assembly 

[hammdo]

Great job! I normally use ‘red’ rubber (brake) grease when doing mc, and calipers. Good for o-rings and assemblies like that.. considering we used that for our race cars, I’d trust it...

https://www.amazon.com/GENUINE-Corrosion-Oxidation-Resistant-TS-2-34-04/dp/B01L63SXSU/ref=asc_df_B01L63SXSU/?tag=hyprod-20&linkCode=df0&hvadid=242122067968&hvpos=&hvnetw=g&hvrand=8000407970440824286&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9026794&hvtargid=pla-568759645110&psc=1

http://www.redrubbergrease.com/

-Don

[N201MKTurbo]

1 hour ago, hammdo said:

Great job! I normally use ‘red’ rubber (brake) grease when doing mc, and calipers. Good for o-rings and assemblies like that.. considering we used that for our race cars, I’d trust it...

https://www.amazon.com/GENUINE-Corrosion-Oxidation-Resistant-TS-2-34-04/dp/B01L63SXSU/ref=asc_df_B01L63SXSU/?tag=hyprod-20&linkCode=df0&hvadid=242122067968&hvpos=&hvnetw=g&hvrand=8000407970440824286&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9026794&hvtargid=pla-568759645110&psc=1

http://www.redrubbergrease.com/

-Don

Probably OK, but different chemicals react weird sometimes. 5606 is quite a bit different than DOT 3/4 brake fluid. I would just lube the parts with 5606 before assembly.

[hammdo]

True, the grease is nice and designed for hydraulic fluids. Used it for years. But would agree 5606 is ‘safe’ bet... 

-Don

[carusoam]

Nice follow up Richard!

Thanks for writing all the detail.

Best regards,

-a-

[PT20J]

Thanks for letting us know. I guess the old pilot adage to undo the last thing you did applies to maintenance too! 

Skip

[Yetti]

If you are using an oil can from the bottom.   Pump 15 times rapidly.   Tends to shove the air bubbles up.  Sometimes must go to 30 pumps.    Oh and use a Turkey Injector to pull fluid out of the reservoir

[RobertGary1]

Also if its been awhile since the system was flushed I'd do a top down bleed to push out the old jelly fluid. Bottom up for air, top down for flush (away from the master).

 

-Robert