What is the specs or Mooney Brake Fluid

[DavePage]

Fellow Mooney folks, is this the correct spec for the Brake / Hydro Fluid  Hydraulic Fluid MIL-H-5606A ?    I've got a 94' Bravo.

I'm about to order it from Aircraft Spruce.

Thanks and Happy Thanksgiving

[PT20J]

Yes. The newer spec is MIL-PRF-5606H, but it's the same thing.

If you are changing the brake fluid, you might consider Royco 782. It's a newer synthetic MIL-PRF-83282 fluid that won't congeal with age like 5606 which is a mineral oil. It is fully compatible with 5606, so you don't have to flush the system.

Edited November 28 by PT20J
Corrected ROYCO 782 not 582.

[Jackk]

5606 seems pretty standard issue.

 

 How old does it have to get before it goes bad?  Seems regardless of the fluid good to purge and replace every half decade or so?

[PT20J]

1 hour ago, Jackk said:

5606 seems pretty standard issue.

Yep, it's been around since the 1930s

1 hour ago, Jackk said:

How old does it have to get before it goes bad?  Seems regardless of the fluid good to purge and replace every half decade or so?

Good question. When I bought my airplane, the logs said the fluid had been replaced about 5 years before. When I drained some from the calipers, it was quite discolored and noticeably thickened. So, every year during the annual inspection I drain about half a cup out of each caliper and it's always a bit discolored. I suspect the heat from the brakes affects it. The fluid upstream wasn't noticeably thickened when I had everything apart to put new o-rings in the master cylinders and replace the flexible lines. But, since I had been draining some each year it was probably pretty new fluid. I don't know the system capacity but it's probably not much more than a pint. Some posters here have reported that 5606 gets pretty gooey after awhile. I'll be interested in other's comments.

The Air Force switched fluids primarily because 5606 is highly flammable.

[Shadrach]

@PT20J meant to say Royco 782.
 

My experience with 5606 mirrors that of @PT20J. 5606 degrades with use over time. How long will depend on use and environment. I have a large can of 5606 in my hangar that dates back to ‘04. It still looks fine. However in the past, fluid from that same can has shown to be slightly discolored at the caliper after 5-6 years in service. When I rebuilt my hydraulic flap actuator for the first time back in the early oughts, there was gelled fluid in the system. It could have been 35 years old. 

I switched to 782 about 10 years ago. Both the flaps and the brakes are a challenge to bleed, I want to minimize the need to open up those systems. For that reason, I want the most durable fluid I can get.

 

[PT20J]

1 hour ago, Shadrach said:

@PT20J meant to say Royco 782.

Oops, thanks for the correction, Ross. I’ve edited the original to avoid any confusion.

[Mooneymite]

Since my Mooney shared many similarities to a 1955 Ford, I always wondered why the brakes couldn't just use DOT 3, or 4.

[DavePage]

Are there any special techniques to bleeding the brakes, other than the depress pedal and open bleeder, close bleeder and release pedal?

Thanks in Advance !

[Ragsf15e]

31 minutes ago, DavePage said:

Are there any special techniques to bleeding the brakes, other than the depress pedal and open bleeder, close bleeder and release pedal?

Thanks in Advance !

Theres a lot of incense burning, balancing acts, low muttering, and some downright voodoo to get the last few bubbles.  
Id use google to search “mooneyspace brake bleeding” and sit down to read with a big cup of coffee.

[1980Mooney]

21 hours ago, PT20J said:

Yes. The newer spec is MIL-PRF-5606H, but it's the same thing.

If you are changing the brake fluid, you might consider Royco 782. It's a newer synthetic MIL-PRF-83282 fluid that won't congeal with age like 5606 which is a mineral oil. It is fully compatible with 5606, so you don't have to flush the system.

 

19 hours ago, PT20J said:

Yep, it's been around since the 1930s

Good question. When I bought my airplane, the logs said the fluid had been replaced about 5 years before. When I drained some from the calipers, it was quite discolored and noticeably thickened. So, every year during the annual inspection I drain about half a cup out of each caliper and it's always a bit discolored. I suspect the heat from the brakes affects it. The fluid upstream wasn't noticeably thickened when I had everything apart to put new o-rings in the master cylinders and replace the flexible lines. But, since I had been draining some each year it was probably pretty new fluid. I don't know the system capacity but it's probably not much more than a pint. Some posters here have reported that 5606 gets pretty gooey after awhile. I'll be interested in other's comments.

The Air Force switched fluids primarily because 5606 is highly flammable.

 

1 hour ago, Mooneymite said:

Since my Mooney shared many similarities to a 1955 Ford, I always wondered why the brakes couldn't just use DOT 3, or 4.

Back in the mid 90's, my plane was owned in a 4 owner partnership.  One of the partners, being helpful during a pre-flight check, noticed the brake fluid reservoir was low and decided to add fluid to the reservoir.  He added DOT-3 automotive brake fluid to the existing 5606 without telling the other partners or logging anything....

On a later flight, one of the other partners had one side of the brakes fail during landing.  Luckily, he kept it on the runway.  They told me it caused the brake fluid and system to gum up. After they had the brake system flushed, repaired and bled, it was the final straw that caused the partnership to break up.  They put the plane up for sale. 

Edited November 28 by 1980Mooney

[PT20J]

2 hours ago, DavePage said:

Are there any special techniques to bleeding the brakes, other than the depress pedal and open bleeder, close bleeder and release pedal?

Thanks in Advance !

The procedure is described in detail in the M20J (and presumably others) Service and Maintenance Manual. You pressure bleed from the calipers up and catch the overflow out of the reservoir until the bubbles stop.

[Yetti]

6 hours ago, DavePage said:

Are there any special techniques to bleeding the brakes, other than the depress pedal and open bleeder, close bleeder and release pedal?

Thanks in Advance !

I pull a fair amount down through the calipers..   with a mity mite.    Then with an oil can 25 pumps up from the caliper.    Refill and then 25 more.   The second person watching the oil reservoir is helpful.   sometimes another 25 pumps is needed after checking the pedal. 

There is one thread about creating a remote mount reservoir on the fire wall.    The Ovations have the reservoir mounted about mid way up on the baggage wall in the comm bay.    This should be above the parking brake. 

[cliffy]

"Brake fluid is NOT just  brake fluid-

Auto (Dot 3,4 or what ever) is a totally different chemical than AVITATION "Brake fluid" (5606)

Due to the materials in the seals and orings in aviation hydraulic systems  (for us little guys) automotive "brake fluid" will dissolve all the seals into a gooey mess thereby causing system failure. Never guess, always use what the maintenance manual says to use  or approved alternates.

Yes 5606  will turn to red jelly inside your calipers after a few years even if you bleed them every year. Disassemble, clean them out and reseal every 5 years or so to stay ahead of the curve.

SOME very old small aircraft actually used automotive brake fluids WAY back when.  And those I think were restricted to brake systems that actually had expanding rubber balloon shoe brakes. Like I said, a long time ago. 

Large modern aircraft  (Boeings, jets. etc) mostly use  phosphate ester fluids like "Skydrol" for its fire resistance. NEVER  even think of using that in our airplanes. Beside one of the side affects of working with Skydrol is- as they say- "mild eye irritation"  BULL CRAP!

If you get it in your eyes you are blind for hours from the pain!!!  Don't ask me how I know.

As a small aside-

Rolls Royce for decades used automotive "brake " fluid in their cars (they actually have hydraulic pumps (2) for brakes and suspension.

All worked fine until the 1980s when they decided to change to a fluid very similar to our 5606 all mineral oil fluid.

Many many Rolls Royce cars were damaged by using the traditional fluid rather than the newer mineral oil fluid. It costs thousands of dollars to repair a Rolls Royce if this happens. It was so bad that they designed a fluid reservoir to only accept a specific bottle hose design so the incorrect fluid could not be put in the car.  

[N201MKTurbo]

FWIW, 5606 will eventually turn into a yellow goo in the Arizona heat. I have only seen that in a 231 we resurrected after sitting in a hangar at Sky Harbor for 10 years.

When we opened the door the first time, everything in the hangar was covered with about a 1” thick layer of a combination of Arizona dust storm and jet exhaust.