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Thread: Tripacer stock expander tube brake assembly procedure question...

  1. #1
    Crash's Avatar
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    Default Tripacer stock expander tube brake assembly procedure question...

    All,

    During a recent flight, my brakes failed... Was a puckering moment for sure. It was due for an annual anyway, so my mechanic and I got to work and tracked the trouble to the left gear -- fluid was seeping out of the expander tube at an alarming rate, so time for O-rings... I think the recent cold snap did me no favors.

    We got it apart and back together, but we have, of course, been stumped by the brake bleeding issue... I think I'm going to mod the bleeder block with Dennis' mod. That said, when you reassemble the cylinder and pistons, is there a recommended way to do that? Should you keep the 'top' piston out and once it's all back together fill it with fluid and insert the piston with the bleeder screw open (and lots of towels)? Or am I just inviting more air into the system... This is about all that stands between me and a flying Tripacer again.

    On the plus side, the mechanics think she's a beautiful bird and in great condition.

  2. #2
    Administrator Steve Pierce's Avatar
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    Default Re: Tripacer stock expander tube brake assembly procedure question...

    I think your terminology is off a bit. The expander tube brakes are on Cubs and Pacers and consists of a rubber expander tube with small brake pads (pucks) around it so when you apply the brake the fluid swells the tube (expander tube) pushing the brake puck into the brake drum on the wheel. From your discription and my knowledge of Tri-Pacers I think you have a drum brake that consists of two brake shoes being pushed out with a piston. Did you look at the bleeding procedure in the Tri-Pacer Owners Manual? From my memory it just takes a fitting to adapt to the existing bleeder fitting. I believe there is a thread on this site as well. Might do a Google search "bleeding Tri-Pacer brakes site:shortwingpipers.org".

  3. #3
    Administrator Steve Pierce's Avatar
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    Default Re: Tripacer stock expander tube brake assembly procedure question...


  4. #4

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    Default Re: Tripacer stock expander tube brake assembly procedure question...

    Here is a picture of a disassembled expander tube brake (minus the actual tube and plus a set of liners):
    Attached Images Attached Images

  5. #5
    Crash's Avatar
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    Default Re: Tripacer stock expander tube brake assembly procedure question...

    Quote Originally Posted by Steve Pierce View Post
    I think your terminology is off a bit. The expander tube brakes are on Cubs and Pacers and consists of a rubber expander tube with small brake pads (pucks) around it so when you apply the brake the fluid swells the tube (expander tube) pushing the brake puck into the brake drum on the wheel. From your discription and my knowledge of Tri-Pacers I think you have a drum brake that consists of two brake shoes being pushed out with a piston. Did you look at the bleeding procedure in the Tri-Pacer Owners Manual? From my memory it just takes a fitting to adapt to the existing bleeder fitting. I believe there is a thread on this site as well. Might do a Google search "bleeding Tri-Pacer brakes site:shortwingpipers.org".
    Steve -- Ha; as I was searching around and looking for examples I jumped to the conclusion that what is on the tripacer was an expander tube (expansion of fluid in the tube to push the pistons out); I couldn't imagine a more primitive mechanism that would be effective on an airplane. As I've mentioned previously, my experience with Pipers is the Tripacer and newer.

    As for bleeding; I scoured all of the material available to me, including the POH. As suggested: the best way to do it is with a pressure bleeder and a vented screw; I just couldn't find a vented screw (Well, the best way is probably to put disc brakes on it... but I digress).

    As for the pressure bleeder, I rigged up my own based on a vacuum bleeder I use on motorcycles -- I found a 1/8" nylon tube coupler, and trimed it to fit into the hole. From there, got a mason jar to use as a pressure vessel and cut two holes in the lid, inserted some rubber grommets, and ran a tube from the bleeder block and my adapter into the jar. Then I just filled the jar with hydraulic fluid and used a tower bicycle pump as my pressure source, with a "beach ball" inflator adapter in the other hole. At the master cylinder, found a nylon fitting to attach to a hose and screw into the filler hole and ran that into a cup. Worked like a charm and was very easy to control the fluid flow -- took about 5 minutes and a 1/2 cup of fluid to bleed the brakes. Got a LOT of air out of the system.

    Now just need this snow to move on so we can complete the annual...

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