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Parking brake issue


bmcconnaha
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1990 m20J.  

Can someone tell me if I am doing something wrong? To engage:  Push brakes down, pull parking brake on.  To disengage: push brakes again, push knob In.  

Problem:  brakes drag still after parking brake is released.  It's a pretty significant drag.  Plane will still roll, but not easily.  Only way to get it released is to really stand on the brakes with the parking brake engaged, and then push the knob in.  

Will bleeding the brakes improve the action? Or, is that down the wrong road?

TIA,

     Bryan 

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I bought my C in 2007. Never used the parking brake . . . . Although one IA was so proud of himself when he "fixed it" at the only annual he did for me (owner assist nit allowed; charged for work that I declined; charged for additional work like the brakes that was never mentioned; his brake "repair" started a leak; etc.).

If it ain't leaking, for God's sake don't start bleeding your brakes!

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6 hours ago, bmcconnaha said:

1990 m20J.  

Can someone tell me if I am doing something wrong? To engage:  Push brakes down, pull parking brake on.  To disengage: push brakes again, push knob In.  

Problem:  brakes drag still after parking brake is released.  It's a pretty significant drag.  Plane will still roll, but not easily.  Only way to get it released is to really stand on the brakes with the parking brake engaged, and then push the knob in.  

Will bleeding the brakes improve the action? Or, is that down the wrong road?

TIA,

     Bryan 

Over time the brake fluid in the system turns to syrup particularly in the wheel cylinders.  We connect a pressure pot to the reservoir and open the bleeders on the wheel cylinders until clear fresh fluid runs out.

Clarence 

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8 hours ago, bmcconnaha said:

1990 m20J.  

Can someone tell me if I am doing something wrong? To engage:  Push brakes down, pull parking brake on.  To disengage: push brakes again, push knob In.  

Problem:  brakes drag still after parking brake is released.  It's a pretty significant drag.  Plane will still roll, but not easily.  Only way to get it released is to really stand on the brakes with the parking brake engaged, and then push the knob in.  

Will bleeding the brakes improve the action? Or, is that down the wrong road?

TIA,

     Bryan 

There is no reason to push the brakes to release. It is just a valve that holds pressure. It will release the pressure if you just open the valve. 
 

On my old Cessna, it has a little mechanism that that locks the master cylinder shafts. You need to push the brakes to release it.

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20 minutes ago, Fly Boomer said:

Clarence, how do you connect the pressure pot in a way that avoids introducing air into the system?

There is always some amount of "air" in the reservoir but the air is above the fluid so it doesnt go into the system. Its basically just a power bleeder most likely. Pressurize the container and it forces fluid out the lines as if you were lightly pressing the brakes. Most of these systems have fluid that they add via siphon as fluid leaves the reservoir but as long as you dont let it get empty you will not add air to the system.

In fact there needs to be an air gap in the reservoir or as the system gets hot the fluid will expand and start to drag the brakes. I've seen several motorcycles at the track get their brakes stuck on because the owner added fluid to the very top before a track day. Fluid expands and the brakes stick on as the pressure builds.

This is for cars but it does the same thing: https://www.motiveproducts.com/collections/import-power-bleeder-kits/products/0100-european-bleeder
 

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If the fluid isn’t too old and you are patient, you can just open the bleeders and let it drip out by gravity. Often the fluid is good after draining half a cup or so. If it takes much than that, it’s probably best to replace it all. Be sure to keep the reservoir full.

Skip

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Someone mentioned it earlier, but you don't have to push the brakes to release them. At least in my 85J. Push the brakes, pull the handle and they are set. Push the handle and they are released. I lock my brakes for engine start up and then again at run-up.

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7 hours ago, Fly Boomer said:

Clarence, how do you connect the pressure pot in a way that avoids introducing air into the system?

The filler on most aft mounted reservoirs is a 1/8” NPT female.  I screw a fitting into this hole, connect my pressure bleeder to it and open the bleeders at the wheel cylinders.

Clarence

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On 6/23/2022 at 3:49 AM, rgpilot said:

It's best not to use parking brakes

I was trained that way too, but I wonder what the conventional wisdom on that is. Are the o-rings more prone to fail from using them than not? My mooney actually did develop a leak at parking brake soon after I bought it. The overhaul was pretty easy though.  

 

 

 

 

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I was trained that way too, but I wonder what the conventional wisdom on that is. Are the o-rings more prone to fail from using them than not? My mooney actually did develop a leak at parking brake soon after I bought it. The overhaul was pretty easy though.  
 
 
 
 

As far as I can tell, the parking brake on our Mooney’s came from an old MTD lawn tractor. It’s not very robust and ironically, it was stamped with “Made in China” (I kid you not).

In the 31 years I have owned my Mooney, no one has gotten it to work. I often wondered if there are other valves that can be used.

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When Maxwells did the PPI and subsequent repairs on my airplane they said they'd fiddled with the parking brake valve and gotten it to work as well as it was going to, which they warned me was probably not going to be enough to trust it to hold the airplane on an incline.  They indicated that they wear internally, can't be effectively overhauled, and are too expensive to justify replacement.    So, basically, I just never use it.  ;) 

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