Hydraulic flaps not working in the cold - again. Electric flap conversion? Experienced shop?

[Oliver]

Hello,

We keep having problems with our hydraulic flaps in low temperatures.
It feels like we're pumping against against an air spring.

We had the hydraulic pump overhauled about two years ago as we were having the exact same issues during the winter.
Everything was perfect over the summer, the symptoms however reappeared as the temperatures dropped to around freezing.

Frankly, we are tired of this and don't see how we can fix this problem for good.

One option could be to convert it to electric flaps, what however appears to be a lot of work. I am also not quite certain of how we would even source the required parts, as I believe that the original conversion kit it not available anymore.

The other option would be to drop it off a shop who has experience with the hydraulic flaps.
We are based out of 1D2, just outside of Detroit, MI. Any recommendations for an experienced shop?

Oliver

Edited February 17 by Oliver
Typos

[cliffy]

If you did your pump the last time maybe you need to reseal the flap actuator this time.

It might be a good idea to replace the hose from the pump to the actuator also at this time

as its as old as the airplane. 

It really a very simple system for any A&P

[Ragsf15e]

1 hour ago, Oliver said:

Hello,

We keep having problems with our hydraulic flaps in low temperatures.
It feels like we're pumping against against an air spring.

We had the hydraulic pump overhauled about two years ago as we were having the exact same issues during the winter.
Everything was perfect over the summer, the symptoms however reappeared as the temperatures dropped to around freezing.

Frankly, we are tired of this and don't see how we can fix this problem for good.

One option could be to convert it to electric flaps, what however appears to be a lot of work. I am also not quite certain of how we would even source the required parts, as I believe that the original conversion kit it not available anymore.

The other option would be to drop it off a shop who has experience with the hydraulic flaps.
We are based out of 1D2, just outside of Detroit, MI. Any recommendations for an experienced shop?

Oliver

@Shadrach is a local expert and has a great thread with pictures.  Just from your description, he’ll probably have an idea and can point you to the thread.  Once working well, they are very reliable.  I had my F for 10 years in Spokane, wa (cold) and they were great.

[Oliver]

8 hours ago, cliffy said:

If you did your pump the last time maybe you need to reseal the flap actuator this time.

It might be a good idea to replace the hose from the pump to the actuator also at this time

as its as old as the airplane. 

It really a very simple system for any A&P

It probably doesn't hurt to also re-do the actuator and the hose between it and the pump, I however don't see how a leak there could cause the current symptoms.
I'm rather thinking that the pump somehow sucks air when it's cold, what is however strange since it doesn't leak any hydraulic fluid.

 

7 hours ago, Ragsf15e said:

@Shadrach is a local expert and has a great thread with pictures.  Just from your description, he’ll probably have an idea and can point you to the thread.  Once working well, they are very reliable.  I had my F for 10 years in Spokane, wa (cold) and they were great.

I know, most pilots seem to be happy with their hydraulic flaps, what makes it even weirder that we keep having these problems.

 

[takair]

How cold are you talking? How fast do the flaps come up in summer?  It might be that the little regulator screw needs adjustment. I can’t recall the details, but  I think it can make the difference and the optimal setting works in both climates. If your talking -40F, maybe a different story. 

[Ragsf15e]

I actually thought that “spring back” sort of feel from the pump handle was specific to having a tiny part installed backwards… @Shadrachwill know…

[cliffy]

If it feels spongy its got air in it

Air can get in anywhere- pump, actuator even a slightly loose hose fitting

If there is resistance on the up stroke the check valve could be blocked.

[Shadrach]

Oliver,

There are a host of small issues that might be causing your problem. My sense is that everything was not perfect over the summer but was acceptable enough for you to think it was functioning properly. The symptoms of having air in the system are exacerbated by the cold. We had a particular harsh winter here. The last time I flew my plane it was in the low teens and the system performed flawlessly. It’s not the system.

I will DM you my phone number. More effective to have a discussion over the phone.

Thanks to @Ragsf15e for conjuring me. I’m pretty scarce around these parts these days.

 

[Ragsf15e]

8 minutes ago, Shadrach said:

Oliver,

There are a host of small issues that might be causing your problem. My sense is that everything was not perfect over the summer but was acceptable enough for you to think it was functioning properly. The symptoms of having air in the system are exacerbated by the cold. We had a particular harsh winter here. The last time I flew my plane it was in the low teens and the system performed flawlessly. It’s not the system.

I will DM you my phone number. More effective to have a discussion over the phone.

Thanks to @Ragsf15e for conjuring me. I’m pretty scarce around these parts these days.

 

Don’t be scarce, I like seeing your opinions/ideas/techniques.  Although there are more important things than “social media” if that’s what MS is, we do like you here!

[Shadrach]

12 hours ago, Ragsf15e said:

Don’t be scarce, I like seeing your opinions/ideas/techniques.  Although there are more important things than “social media” if that’s what MS is, we do like you here!

It’s not that I’ve lost interest. I think I mentioned to you in a DM several months ago that I was embarking on a new professional endeavor.  Posting here has become a more delicate proposition for that reason. I still check in from time to time to see if I can be of help.

[A64Pilot]

Flush the system well, I mean really well.

5606 turns to syrup when it gets old in Summer temps and this Syrup turns to grease in cold weather, grease won’t pump well, pulling a Vacuum is likely the springy feel you have, and it will suck in air too.

Consider changing to 83282 (Aeroshell 31) but there are other brands, it won’t turn to syrup when it gets old. It just a new synthetic replacement and it’s 100% miscible with 5606 with no issues. 

It’s been around for a long time so if it were going to be a problem we would have known decades ago

Edited February 21 by A64Pilot

[Shadrach]

I switched to 83282 (Royco 782) the last time I did maintenance on my system.  That being said, 5605 vs 83282 never made an operational difference. Almost all of the problems that I have encountered with the Mooney flap system have been the result of someone, for some reason, deciding that the system needed an "overhaul."  As soon as humans disturb the system a host of potential issues come to the forefront.

[Oliver]

Thank you very much again for all your responses.

The flaps were working perfectly and only started to act up once the temperatures dropped to around freezing.
When we overhauled the pump, we alos very thoroughly flushed the system and filled it with fresh fluid.

Shadrach offered a chat, which I gladly accepted, before we rip everything apart again. 

[Shadrach]

9 hours ago, Oliver said:

Thank you very much again for all your responses.

The flaps were working perfectly and only started to act up once the temperatures dropped to around freezing.
When we overhauled the pump, we alos very thoroughly flushed the system and filled it with fresh fluid.

Shadrach offered a chat, which I gladly accepted, before we rip everything apart again. 

Look forward to speaking next week.

Just so we’re clear on working “perfectly”. 
 

 

[Oliver]

8 minutes ago, Shadrach said:

Look forward to speaking next week.

Just so we’re clear on working “perfectly”. 

I would say that's how ours were. Until they weren't.

Maybe they retracted a bit slower. They however also started to come down immediately and hydrolocked after a little over 4 strokes.
We however found it quite challenging to fine adjust the retraction speed as simply tightening the lock nut already impacts the speed.

[MichiganMooney1]

On 2/21/2025 at 10:42 PM, Oliver said:

Thank you very much again for all your responses.

The flaps were working perfectly and only started to act up once the temperatures dropped to around freezing.
When we overhauled the pump, we alos very thoroughly flushed the system and filled it with fresh fluid.

Shadrach offered a chat, which I gladly accepted, before we rip everything apart again. 

Yes. I live in SW MI also. I have had (and have today) the same experience in the cold. I am thinking that the fluid gets viscos at freezing temperatures and it "gulps" air. But reading these posts I have understood that the "spring back" of the handle indicates a vacuum in the system aft of the pump. I and my IA are struggling with the bleeding process and it looks like we will have to pressure/vacuum bleed it. If anyone has an answer to the cold temperature problem and as to why air gets into the system I would like to know. Just like your problem, they work great in higher temperatures but when it gets cold problems occur.

Thanks for your help.

P.S. Those leather seals in the pump piston are a joke. If anyone has a modern fix for this, it would be greatly appreciated!

[47U]

3 hours ago, MichiganMooney1 said:

P.S. Those leather seals in the pump piston are a joke. If anyone has a modern fix for this, it would be greatly appreciated!

Got a part number for the leather seal?  (I am probably confused… again.)

[M20F-1968]

On 2/18/2025 at 7:17 PM, Shadrach said:

Oliver,

There are a host of small issues that might be causing your problem. My sense is that everything was not perfect over the summer but was acceptable enough for you to think it was functioning properly. The symptoms of having air in the system are exacerbated by the cold. We had a particular harsh winter here. The last time I flew my plane it was in the low teens and the system performed flawlessly. It’s not the system.

I will DM you my phone number. More effective to have a discussion over the phone.

Thanks to @Ragsf15e for conjuring me. I’m pretty scarce around these parts these days.

 

I am in Boston and have never had a problem with the system in the winter.  It is a PITA to maintain and change pumps, but once it works it works.

Of great help is to make lines that access all the pressure pot fittings and fittings in the system.  I have a large pressure pot and a smaller one for the front.  

When filing the system, open it in the middle, hooking a line to the outflow of the pump, and push fluid forward bleeding it out the front.  Then rehook up the rear line to the pump, and push brake fluid forward and bleed in out the front.  The hardest part to prime is the pump itself.

John Breda

 

[MichiganMooney1]

On 3/18/2025 at 3:22 PM, 47U said:

Got a part number for the leather seal?  (I am probably confused… again.)

I found these online.

https://www.knots2u.net/he625-he1506-mooney-m20-series-hydraulic-flap-actuator-65-67-m20c-m20d-m20e-m20f/