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Brakes and master cylinder


FastTex

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I know this topic has been discussed multiple times but here is my situation:

- Reseal kits applied to both brakes

- Left brake, even after multiple attempts by my A&P to bleed, still need push down a lot to work

- The recommendation is to replace the master cylinder which appears to be worn out

-  Part number I got is 850012-501

- Asked Spruce: no joy.

- Asked Lasar: that old part is no longer available but Mooney makes a retrofit kit (p/n 940076-000) $2537.14!

Is there any other place? Also, even if I find one at the salvage yard, how do I know it works?

 

Any idea/suggestion is welcome!

Thanks.

 

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4 hours ago, FastTex said:

I know this topic has been discussed multiple times but here is my situation:

- Reseal kits applied to both brakes

- Left brake, even after multiple attempts by my A&P to bleed, still need push down a lot to work

- The recommendation is to replace the master cylinder which appears to be worn out

-  Part number I got is 850012-501

- Asked Spruce: no joy.

- Asked Lasar: that old part is no longer available but Mooney makes a retrofit kit (p/n 940076-000) $2537.14!

Is there any other place? Also, even if I find one at the salvage yard, how do I know it works?

 

Any idea/suggestion is welcome!

Thanks.

 

Ask the person making the recommendation what they believe is wrong with the original (but newly resealed) cylinder that will be remedied by replacing it.  Was the cylinder bore rough or corroded? Our brake cylinders are simple devices. The internal seals wear but there is little else to fail. Your MX should have identified any other issues when the cylinder was apart. If no issues were identified during reassembly, the cylinder was either misassembeld or the mechanic has failed to bleed the system (likely) which is no easy task. Throwing $2500 at a new cylinder is not going to make it easier to bleed and it will likely piss you off when the same challenge manifests itself. 

Ask your mechanic if he has applied vacuum to the top of the system. Mooney brakes can be a challenge to bleed especially if don’t know what you don’t know.

Edited by Shadrach
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I doubt your master cylinder is "worn out"    There are only 3 or 4 O rings in a "reseal Kit"    depends on the cylinder.

You would be good to search google mooney space master cylinder.   You will find the cleavland part numbers for the master cylinders that fit your plane.   Pretty sure your S&M manual will help you out.   Also the cleaveland manual is online.  The attached one may work for you.

 

cleveland_wheelbrakes_mm.pdf

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One other thought.  It should be pretty easy to verify if the brake cylinder is the problem.  It may take additional hose and a few extra fittings but your mechanic should be able to bleed and cap the output on the cylinder to ops check.  Opting to order a new cylinder before verifying the existing cylinder is soft would be malpractice in my humble opinion.

Edited by Shadrach
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Just now, Shadrach said:

  Opting to order a new cylinder before verifying the existing cylinder is soft would be malpractice in my humble opinion.

Especially since replacement is over $2500, and it still won't be right until it's bled properly.

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4 hours ago, Andy95W said:

Especially since replacement is over $2500, and it still won't be right until it's bled properly.

I was having trouble bleeding the [angled] master cylinder for the clutch in my truck [which also has a low spot in the tubing, by design!] after replacing it. AutoZone sold me a prefilled assembly, no bleeding required. Does no one do this for airplanes???

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It would actually be pretty easy to pre-fill the actuator prior to installation.  (And its definitely a good idea when it comes to the hydraulic flap actuator).

The problem with the brakes are the brake lines between the master cylinders and the calipers- they aren't a downhill run the entire way to the calipers.  So the problem remains that if you can't flow enough brake fluid, you'll never quite get the last little bit of air out.  (I bet if you could suspend a Mooney at a 45° nose up angle and then bleed the brakes, we wouldn't be having this discussion.)

I don't remember if it was Ross, Rich, or Yetti, but someone mentioned flying the airplane in nose-high banked attitudes and manipulating the brake pedals to help the remaining air rise through the system.  It seemed to help mine when my right brake was a little bit softer than the left.

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3 hours ago, PilotCoyote said:

When you say “push down a lot”, can you clarify whether you mean increased pedal travel or relatively high pedal pressure, or both?

As far as salvage yards go, a reputable one will refund 100% if part doesn’t work.

In order to break, instead of tapping the pedal (like the right one) you need to "travel" the left pedal way more...

 

 

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3 hours ago, FastTex said:

In your guys experience how many hours should it take to replace the master cylinder?

Is the plane already opened up? Getting to them is more work than replacing them. They are held in by two cotter pins and two brake lines. If you have it opened up it only takes a few minutes to change them. If you are talking starting with the plane all together, it could take 3-4 hours or more if bleeding is a PITA.

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5 hours ago, FastTex said:

In order to break, instead of tapping the pedal (like the right one) you need to "travel" the left pedal way more...

 

 

This is an air issue and that air is likely downstream of the master cylinder. You need to put vacuum on the system. Other things may work over a period of time (high altitude flight, high AOA, etc) but your best bet at getting the air to evacuate the system is to put a vacuum on the reservoir and actuate the cylinder in question several times.

Edited by Shadrach
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5 hours ago, FastTex said:

In your guys experience how many hours should it take to replace the master cylinder?

Read cleavland manual and find the Oring numbers, Panel off, remove cylinder, 3 new orings in cylinder, replace cylinder.   Clean up center panel for leaked fluid, replace panels.   Probably took me 2 hours or less.   Bleed brakes was about 30 minutes for 2 guys.   One pumping, one managing the fluid in the reservoir. 

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  • 1 year later...

The part that seals off the high pressure side that applies pressure to the system does not come

in the rebuild kit. It looks like leather inside of the head of the nail shaped brass part. I installed an o-ring

in it but it wont seal off. This o-ring was smaller than the shaft o-ring. This is the part that gives everyone

trouble. I don't have a solution.

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