Slow speed brake deployment lubrication or vacuum problem?

[RobertE]

It's winter in NorCal so I'm flying in near (but not quite) freezing temps, but lately I've noticed some hesitation in extension and retraction of the leaves.  If I just lubricate will that likely fix the problem?  Anything special I should know?  Thanks.

[carusoam]

Do the vacuum driven ones have a clutch like the electric ones..?

Accidently lubing the clutch would not be helpful.

cold temperature has a tendency to make polymer hoses stiffer. Stiff hoses may begin to not have an airtight fitting on their barbs.

Does one side operate differently than the other?  With the electric clutch the wear is individual.  One brake will stop operating before the other...

From the precise flight website, I couldn't find vacuum info.  But they have email and other contact information if you can't get an answer here...

https://preciseflight.com/resources/doc/541SMAN0001D.pdf

Hope this may help some,

-a-

[Piloto]

The vacuum servo rubber boot is less flexible in cold temps.

José 

[170driver]

I had the brakes on my Mooney retract asymmetrically last summer - pilot side took about a minute to stow away. Obviously not a temperature issue - I aimed a shot of Tri Flow at each pivot point, from the slot in the wing surface. All worked well after that, so no ill effects from lubrication.

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[N201MKTurbo]

You should remove them from the wings, take them apart and lube them properly.

[DonMuncy]

On my 231 with Precise flight electric speed brakes, infrequently, when I disengage them, after use, one of them will not retract all the way. I think it stays up about 1/2 inch or so. However, when the master is turned off, it retracts completely. Does anyone have any knowledge of the electrical circuit that would explain how turning  them off would not retract them completely, but switching the master off would. Because the master will cause them to retract, I have trouble believing it would be a lubrication problem. Thoughts?

[amillet]

I had the same issue Don.  Greg at Advanced Aircraft in Troutdale pointed out that Precise Flight recommends pulling the units out every 1000 hours and returning them to the factory.  We did this and they now work like new again

[amillet]

Cost for factory repair of speed brakes $1.2AMU for both

[carusoam]

That service includes changing out the clutches.  My O had about 1500 hours on the airframe before one of the brakes started to misbehave...

Best regards,

-a-

[DonMuncy]

Thanks for the info. This is one of those instances where I can choose when to spend that $1200.

[anthonydesmet]

Gents,

Had the same issue as RobertE last spring and when I went for my annual I contacted Dave Mollman at Precise Flight.  He sent me the ICA (Inspection for continued Air worthiness).  My mech and I pulled the boxes and inspected, cleaned and lubed IAW the ICA.  Large amount a gunk came out of the vacuum houses which was most likely preventing the vacuum system to work properly hence the slow deployment and retraction.  They work smooth as silk ever since and they were installed in 1993.  

I agree with Jose though about the cold but I still recommend first to look in your logbook and see the last time your brakes were checked out IAW the ICA.  If your brakes are fighting clogged lines and a lubrication issue you're really not helping them out in the cold weather.  My ICA is a part of my annual now. I have attached the ICA for my model speed brakes (100's).  If you don't know your model/serial number and its not in your logbook you can get the serial number off of one of the brakes by pulling the lower inspection panel.  You should be able to use an extended mirror and a flashlight. Call Dave and he will be able to tell you the model number, year they were installed and who installed them, assuming you're a Precise Flight owner.  He will also send you the correct ICA.  I also remember reading in a post on MAPA (might have been from Don Maxwell) that you can't use any type of lube so definitely do some research.

Don, not sure if this will help your issue though but Dave maybe able to walk you through it.  There maybe a mechanism that allows the complete removal of the vacuum pressure when all electrical power is removed however...meaning your lines still maybe clogged...but I am just spit balling....

doc00093120150629102302 (1).pdf

[DonMuncy]

 

 

Don, not sure if this will help your issue though but Dave maybe able to walk you through it.  There maybe a mechanism that allows the complete removal of the vacuum pressure when all electrical power is removed however...meaning your lines still maybe clogged...but I am just spit balling....

 

Are you saying the brakes are vacuum operated with electrical activation. If so, where does the vacuum come from. Uses engine vacuum pump, or has its own vac pump? Even though I have them, I know very little about them,

[N201MKTurbo]

Don,

The electric speed brakes have a motor to raise and lower them with limit switches to stop them in the extended and retracted position. They also have clutches that disengage the motors and allow the springs to fully retract them. The clutches are there for the asymmetrical deployment sensor to retract them if they are mismatched (not that big of a deal actually) When you turn off the master it disengages the clutches and allows them to fully retract, usually with a bit of a clunk. If they are not retracting fully, it is usually a stuck limit switch.

[WilliamR]

 

Are you saying the brakes are vacuum operated with electrical activation. If so, where does the vacuum come from. Uses engine vacuum pump, or has its own vac pump? Even though I have them, I know very little about them,

Don, Precise Flight manufactured two systems for their speed brakes; vacuum and electrically actuated.  Not sure which you have.  I know many/most of the 252s came with vacuum actuated brakes.  The vacuum source is from the engine driven vacuum pump, or if your also fortunate enough to have a standby electric driven vacuum pump, there too.

 

William

 

[aviatoreb]

If they are vacuum powered - 

the vaccum power is converted to mechanical power by filling rubber bellows.  I once had a small rip in my rubber bellows develop and that brake would not deploy well but still sort of worked.  The rubber needed to be replaced. It was not a big or expensive fix if I remember correctly.  It was 4 or 5 years ago.

[DonMuncy]

Thanks for the responses. I thought mine were all electric.

 

[RobertE]

Gentlemen: 

Excellent info.  I've determined I have vacuum style brakes and note that Precise Flight has only the newer, electrical maintenance manual on their website.  Anyone got the manual for the vacuum style?  I think the cables are too loose but don't know the proper amount of play.  Thanks.

[anthonydesmet]

Robert,

Give Dave Mullman at Precise Flight a call with one of your serial numbers. He will probably send you what you need.

If you just want the inspection procedure and install procedures and what you need to do for the ICA I uploaded it with my post above. If you cant get it to download let me know and I'll send it but not sure what series SB's you have or if your just looking for an entire manual or if PF has anything more than what I have.

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[RobertE]

Thanks very much.  I'll go to Precise Flight.  The document you earlier attached seems to be for the electrically activated brakes, not vacuum, or am I reading it wrong?

[kortopates]

1 hour ago, RobertE said:

Thanks very much.  I'll go to Precise Flight.  The document you earlier attached seems to be for the electrically activated brakes, not vacuum, or am I reading it wrong?

That's correct, the documentation Anthony posted is for older electrical speed brakes only which have nothing in common with the original vacuum brakes. There is no documentation to be had on the older vacuum brakes.

The original vacuum brakes contain a sealed bearing that can be replaced but entire brake must be de-riveted to get to  it - not an easy task. Since its a "sealed" bearing, lubing it isn't really recommended. The rubber vacuum bellows is no longer available from Precise Flight; one would have try to patch any leaks or tears (but I have not been down that road - mine from '86 still looks pristine). They still had springs and conduit cables the last time I talked to them not long ago. Installations from 80's would most likely be suffering from the conduits breaking down - they are just like bicycle cable and when the conduit gets brittle with age and falls apart it can prevent the cables from fully deploying the brakes and causes them to stick up since the little spring on the brakes are unable to fully overcome the friction in the ruptured conduit. Conduit cables are never going to need adjustment after installation - they don't stretch; appearance of such is pointing to a broken failing conduit cable.

The first step in diagnosing any speed brake issue is first determining which type/kind you have and then familiarizing yourself without how the system operates.

[RobertE]

Perfect.  Thanks.

[Guest]

The vacuum pot as well as the vacuum solinoid are located under the back seat, accessible by removing belly inspection panels.

The last one I fixed had a hole in the rubber boot, we sent it to Brittain Industries for replacement, quick and realatively cheap.

Once exposed you can actuate the brakes by pulling the cables individually.  Use of a motorcycle throttle cable lubricator will help with the cables.  The speed brake will likely have to be removed from the wing for cleaning and lubricating of the blades and pullies.

Clarence

Edited January 31, 2016 by M20Doc