M20J parking brake question

[PT20J]

I recently did an insurance checkout for a new owner in a really nice 1978 M20J. It was kind of a nostalgia trip since my first Mooney 35 years ago was a 1978 J. Anyway, the seller had mentioned that he didn't trust the parking brake. I've always found the parking brake to be pretty good, so I tried and it worked fine. Until we wanted to taxi, that is. Then the left brake dragged. After half a mile of taxiing and repeated applications it eventually released. I've never had to deal with the intricacies of Mooney brakes, but looking at the IPC it seems that the parking brake valve cuts off fluid return to the reservoir for BOTH master cylinders. So, I'm at a loss to understand why the left brake hung up. Anyone have any ideas?

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[EricJ]

Yes, the parking-brake valve is single-input, single-output, so there's no differentiation between the sides other than one caliper may be more sensitive than the other to getting sufficient pressure release.    I've never bothered with mine, so I don't know the answer to the question.    Maxwells did my pre-buy and a bunch of work when I bought the airplane.    The parking brake valve was one of the squawks they'd identified, and Don indicated that they're bespoke units that are expensive to replace, so they just rehab them as best they can.   He pretty much said it'll sort-of work, but don't rely on it especially on a slope.    I think I've used it twice since I've owned the airplane and it wasn't great.    I think they're just generally not a great system.

[PT20J]

31 minutes ago, EricJ said:

Yes, the parking-brake valve is single-input, single-output, so there's no differentiation between the sides other than one caliper may be more sensitive than the other to getting sufficient pressure release.    I've never bothered with mine, so I don't know the answer to the question.    Maxwells did my pre-buy and a bunch of work when I bought the airplane.    The parking brake valve was one of the squawks they'd identified, and Don indicated that they're bespoke units that are expensive to replace, so they just rehab them as best they can.   He pretty much said it'll sort-of work, but don't rely on it especially on a slope.    I think I've used it twice since I've owned the airplane and it wasn't great.    I think they're just generally not a great system.

Interesting. The one in my 1994 J is rock solid, but I notice that Mooney changed the valve at S/N 24-0764. I'm betting that the fluid is old and thick and needs to be flushed.

[kortopates]

it could be old O-rings needing replacement or the even the rigging cable slipping or not being secure. Takes very little effort to rebuild them and re-rig the cable. In the process of doing do the issue should become apparent.


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[Bartman]

I remember having mine worked on about 15 years ago. They found the hydraulic fluid had turned to gel and after flushing the entire system it worked, but I have never used it. I am either in my hangar with a chock or on the ramp with chock on the nose, and if anything more than a fuel stop or meal they are on all 3 wheels. In fact, the line personnel usually ask me to be sure the parking brake is disengaged. 

Long story short my parking brake is used so infrequently that I do not trust it to engage, or to disengage, therefore I do not use it. 

[Hank]

The first annual after my IA retired, the new guy was so proud of himself for "fixing" my parking brake. I'd owned her for more than a decade, had never used it and wasn't sure if one was even installed. He also didn't ask, just did it--a small item from the many points of contention that year. Haven't been back . . . And I've had nothing but leaking brakes since then, but never before. Hopefully the current fix [try #3] will turn out to be the winner.

As far as I know, that genius was the only one to use the parking brake, and when I picked it up after annual and couldn't taxi was the first time that I [eventually] ever saw it on and let it go.

I do carry lightweight chocks made from 2" x 2" aluminum angle rescued from the trash at work--they live on the hatrack.

[PT20J]

I must be the only one that uses my parking brake. I sometimes park on unlevel ground and use it to prevent rolling until I get chocks under the wheels. I've found the parking brake on both my 1978 J and 1994 J to work really well.

[Fly Boomer]

On 5/8/2023 at 10:08 PM, PT20J said:

Interesting. The one in my 1994 J is rock solid, but I notice that Mooney changed the valve at S/N 24-0764. I'm betting that the fluid is old and thick and needs to be flushed.

Sounds right.

[A64Pilot]

I never use parking brakes, in fact I’m so much against them that I don’t think they should even be installed, only ones I’ve seen that were any good were on the Thrush, those were installed inline with each master cylinder that was right beside your knees, very easy to remove or replace, I just ignored them.

I don’t like them because if you lock the parking brakes when they are hot, the trapped fluid can heat up and expand and pressures go way up, causing leaks, and because when locked they are in contact with the hot disc, the caliper heat goes way up degrading the O-rings and decomposing the fluid.

Plus more than one tailwheel has gone over on its back or ground looped due to a stuck on parking brake.

But lastly I’m going on my tirade to convince people to STOP USING 5606, it’s an old antiquated fluid that turns to sticky goo with age and causes all kinds of problems, that you can completely eliminate.

For goodness sake replace it with 83282, which does NOT turn to goo and is just a much better choice, it’s been around since the early 80’s, it’s not new and there is NO downside to it, just upsides. It mixes with 5606 perfectly there is no perfect flushing required or anything.

https://www.aircraftspruce.com/catalog/lgpages/aeroshell08-14635.php

On edit, if your a person that flies in temps more than -40F then you need 85257, I’ve never used it myself, I assume it’s harder to find and cost more but don’t really know.

 

[Fly Boomer]

1 minute ago, A64Pilot said:

I never use parking brakes, in fact I’m so much against them that I don’t think they should even be installed, only ones I’ve seen that were any good were on the Thrush, those were installed inline with each master cylinder that was right beside your knees, very easy to remove or replace, I just ignored them.

I don’t like them because if you lock the parking brakes when they are hot, the trapped fluid can heat up and expand and pressures go way up, causing leaks, and because when locked they are in contact with the hot disc, the caliper heat goes way up degrading the O-rings and decomposing the fluid.

Plus more than one tailwheel has gone over on its back or ground looped due to a stuck on parking brake.

But lastly I’m going on my tirade to convince people to STOP USING 5606, it’s an old antiquated fluid that turns to sticky goo with age and causes all kinds of problems.

For goodness sake replace it with 83282, which does NOT turn to goo and is just a much better choice, it’s been around since the early 80’s, it’s not new and there is NO downside to it, just upsides.

https://www.aircraftspruce.com/catalog/lgpages/aeroshell08-14635.php

 

Totally with you regarding the 5606, but I think @PT20J nailed the best use for parking brake — just long enough to exit the airplane and get chocks in place.  Then release.

[Nippernaper]

The OP symptoms sound exactly like the trouble I had after acquiring my '78J.  After having the master cylinders rebuilt system flushed, etc., it turned out the left master cylinder on the pilots side would physically conflict with another component when fully depressed, and become hung-up, unable to release.  This was not a hydraulic issue, but a physical conflict between components which would prevent the cylinder from retracting.  When you apply the parking brake, you have a tendency to push harder on the brakes then just about any other time, and this led to the issue only showing up when using the parking brake.  You might want to have the owner check this.

[Pinecone]

11 hours ago, PT20J said:

I must be the only one that uses my parking brake. I sometimes park on unlevel ground and use it to prevent rolling until I get chocks under the wheels. I've found the parking brake on both my 1978 J and 1994 J to work really well.

I use mine.  I set it before start, during runup, and before shutdown.  Mine holds fine, but for runup, I guard the pedals.

After shutdown, I may release it, but with me in the seat in case it rolls.

[Hank]

2 hours ago, Pinecone said:

I use mine.  I set it before start, during runup, and before shutdown.  Mine holds fine, but for runup, I guard the pedals.

For runup, I just hold the brakes. Same as when I was a student in the old 172.

[201Mooniac]

15 hours ago, PT20J said:

I must be the only one that uses my parking brake. I sometimes park on unlevel ground and use it to prevent rolling until I get chocks under the wheels. I've found the parking brake on both my 1978 J and 1994 J to work really well.

Not the only one, I use it similarly and find it works well

[1980Mooney]

17 hours ago, PT20J said:

I must be the only one that uses my parking brake. I sometimes park on unlevel ground and use it to prevent rolling until I get chocks under the wheels. I've found the parking brake on both my 1978 J and 1994 J to work really well.

Me too. I use it all the time - works great for over 24 years without overhaul.  

[GeeBee]

On 5/9/2023 at 10:19 PM, PT20J said:

I must be the only one that uses my parking brake. I sometimes park on unlevel ground and use it to prevent rolling until I get chocks under the wheels. I've found the parking brake on both my 1978 J and 1994 J to work really well.

Same here. It is there for use until you chock, just like the POH says.

 

[Yooper Rocketman]

On 5/9/2023 at 9:19 PM, PT20J said:

I must be the only one that uses my parking brake. I sometimes park on unlevel ground and use it to prevent rolling until I get chocks under the wheels. I've found the parking brake on both my 1978 J and 1994 J to work really well.

I use mine all the time like described above.  

Tom

[Echo]

I used mine every run up instead of standing on brakes.  Worked great in a 80 J/Missile.

[sleeper-319]

On 5/9/2023 at 7:19 PM, PT20J said:

I must be the only one that uses my parking brake. I sometimes park on unlevel ground and use it to prevent rolling until I get chocks under the wheels. I've found the parking brake on both my 1978 J and 1994 J to work really well.

I use mine on occasion for the same reason (Unlevel ground). It works fine. As kortopates says, they are really simple mechanically, and very easy to overhaul.