Brake Bleeding - Help please!

[Awful_Charlie]

Could do with a bit of wisdom for the community here. Just come out of Annual, where I got new brake pads, but one calliper had to come off to clean up and replace the seals, and the master cylinder got new seals at the same time. My A&P spent several hours with a pressure bottle forcing fluid up from the bottom, but the results weren't great. I helped him pump stuff down from the inside using the pedals whilst he operated the bleed screw, and it was still no better. We went back to the pressure bottle and forced another gallon through the system, and got a few more bubbles to show in the reservoir return line, but the action is still far from good.

 

Has anyone got a good method for purging all the air out of the lines? We are considering making an adapter up for the bleed nipple so as to be able to push a higher flow, but so far this is driving us crazy! Another through is to do this on jacks so the flow from the master cylinders to the reservoir isn't 'downhill', but it seems like a long shot

 

TIA

 

Ben

[Mooneymite]

Do you have pilot/copilot brake pedals, or just one set of master cylinders?

[Awful_Charlie]

Yes, brakes both sides, It is the left hand brake that is causing us the problem, and it is equally bad from the P1 or P2 position

[Mooneymite]

Hmmmm. I have no experience with dual brakes. With single master cylinders, pumping fluid up from the bottom does the trick. Perhaps the dual installation is complicating the process?

[MB65E]

I've had good luck with bleeding brakes with the gear retracted...bleeding up from Bottom to top.

Using a pot with Constant flow and good pressure helps, I'm sure your using somthing acceptable.

Good luck.

-Matt

[MARZ]

Try depressing one position's pedal and bleed, then switch to the other and bleed

[Bolter]

Don't dismiss problems on the co-pilot side if you did not also rebuild those cylinders.  I chased bleeding issues for a long time.  Losing pressure in the pilot's brakes tracked down to (amongst other things) o-rings on the co-pilot brake maser cylinders.  This was especially unintuitive as the co-pilot brakes would still be firm after the pilot side was getting soft, though eventually both went soft when enough fluid was lost.  That was the last repair made, and then no problems for >2 years and counting...

 

As a side note, we played games with bleeding, pressurizing up, putting the plane on jacks with different ends high, and in the end, when everything was right internally, it could be bled just fine sitting on its gear.

[rangermb]

Had the same issue with my J. We thought that the fact that the brake cylinders being pretty much level were allowing air to hide. We jacked up the nose to get some angle working and out came the air.

[ovation0219]

Try plugging off the co pilot while bleeding pilot side and then reconnect and bleed co pilot side. that worked for me.

[N601RX]

Some of the master cylinders have a slot milled into the end piece that helps get the trapped air out. When reassembling this has to go up to be effective. Once their together you can't tell if its up or sideways unless you put a mark on the outside.

[N201MKTurbo]

219 has the right idea. With dual brakes air can get trapped in either master cylinder loop. When you bleed the system the fluid just flows around the air instead of forcing it through the system. Disconnect and cap off the lines from the resovior to one of the master cylinders and bleed the system from bottom to top. Then reconnect that one and cap off the other one and bleed again. This should get all the air out.

[N601RX]

I know Mooney has used 2 different set ups for the copilot brakes. The retrofit kit that mooney provided for the C-K models plumbs them up in series. When you press the pilot side brakes the fluid flows out of the pilot side master cylinder and through the copilot side master cylinder and then out to the respective wheel cylinder. There was also another setup they used that has them in parallel with a shuttle valve.

[Sven]

The brakes and flap pump are similar. Take a look at this thread and look for Shadrach's explanation and on page 2 for my pictures. I hope that helps.

 

-Sven

 

http://mooneyspace.com/topic/10208-flap-pump-questions/page-2

[Awful_Charlie]

Thanks everybody - keep 'em coming. I'll report this lot to Fritz tomorrow and see how it goes.

 

FWIW, I have the 'post shuttle valve' installation

[jeffschnabel]

always back bleed and pump them up from bleed screw on calipers. let gravity do the work of eliminating air bubbles.  see maint manual.  if dual brakes, you have to depress each set of peddles to move the shuttle valve into proper position to back bleed.  see maint manual.    if caliper leaking push puck out and put new o-ring in  before reinstalling I always look at bore and use a light scotch bright pad. they wont leak again for a long long time.  cleaning bore is essential or it will leak again.

[Marauder]

2 hours ago, jeffschnabel said:

always back bleed and pump them up from bleed screw on calipers. let gravity do the work of eliminating air bubbles.  see maint manual.  if dual brakes, you have to depress each set of peddles to move the shuttle valve into proper position to back bleed.  see maint manual.    if caliper leaking push puck out and put new o-ring in  before reinstalling I always look at bore and use a light scotch bright pad. they wont leak again for a long long time.  cleaning bore is essential or it will leak again.

Can you explain more on this shuttle valve? Are you talking about the valve in a dual brake system? I am having a bear of a time getting air out of my system that only has pilot side brakes. 

[mikeylop]

I rebuilt my master cylinders and to avoid bleeding issues, I submerged them in a small bucket of 5606 and pumped them several times until full, then capped them.  I installed then quicly connected them.  It made for easy bleeding.  Only took 5 mins to bleed each side. 

P.S.  I only have pilot side brakes

[jeffschnabel]

On ‎12‎/‎7‎/‎2018 at 12:57 PM, Marauder said:

Can you explain more on this shuttle valve? Are you talking about the valve in a dual brake system? I am having a bear of a time getting air out of my system that only has pilot side brakes. 

shuttle valve not installed on single sets of brakes. only some dual brake setups.   did you get it sorted out or are you still having issues ?

[RLCarter]

16 minutes ago, jeffschnabel said:

shuttle valve not installed on single sets of brakes. only some dual brake setups.   did you get it sorted out or are you still having issues ?

thought the shuttle valve was a Beech thing

[Marauder]

shuttle valve not installed on single sets of brakes. only some dual brake setups.   did you get it sorted out or are you still having issues ?

It’s gotten to a point of being flyable. Still feels a little softer than before but I can now stop normally and able to hold the brakes during run up.

The bleeding was a nightmare. Between trapped air, crappy bleeders and a few surprises it took way longer than it should have.


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