Seneca - brake bleeding - HELP!

Seneca - brake bleeding - HELP!

Hi folks

I have a PA34-200T, and it's proving to be almost impossible to bleed the brakes.

Does anyone have any sure-fire way to bleed the brakes on this plane?  It's apparently a lot harder than it has any right to be - any help would be much appreciated.

Thanks!

Kevin

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Re: Seneca - brake bleeding - HELP!

If the brake lines on a Seneca are similar to a PA28, then brake bleeding will be a PITA.

I can't remember all the details, but brakes are best bled "in reverse", by using a pressurized source of brake fluid at the brake cylinders, and then flushing the air upwards to the fluid reservoir.

Alternatively, you can create a closed loop of brake fluid by running a line from the reservoir to the brake cylinder. Pumping the brakes circulates the fluid and allows air to escape at the reservoir.

There are two good reference articles that you should read in Light Plane Maintenance: Oct/2005 and Aug/2007.....both deal with bleeding Piper brake systems. Good luck.

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Re: Seneca - brake bleeding - HELP!

My PA28 was really hard to bleed after replacing Master Cylinder seals. We started with the parking brake handle, then right main, then left. I was told that air could get trapped in the parking brake handle when the system was opened, so we made sure to operate the handle to bleed.

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Re: Seneca - brake bleeding - HELP!

Bleeding Cherokee brakes has always been a point of frustration.  However, I read about a technique that works very well and I have been successful with it every time I have tried.  Ironically, this technique is the subjects of an artile in this month's Pipers magazine.

Fist you will need to get some clear plastic tubing.  I can't remember the diameter, but you want it to fit over the brake bleeder screw.  For the PA28 you should have about 25 feet, but for the seneca you may need a bit more.

- Cut this length of tube in half so you have one for each wheel cylinder.

- Attach one side of the tube to the bleed screw.  Use safety wire around the lip of the tubing to ensure it will not pop off the screw.

- Using masking tape or duct tape to secure the tubing, run the tube up to the wing leading edge, toward the fuselage and over the top, then down the windscreen into the brake fluid resevoir.  (NOTE: This is for the PA28.  I don't know where the resevoir for the Seneca is located, but the idea it to run the tube into the resevoir while ensuring the the tube rises above the resevoir elevetion at some point.)

- Make sure that the resevoir is full.

- Open the bleed screws.

- Get in the plane and alternately pump the hand brake and toe brakes about 3 to 5 times.

- Top off the resevoir (much of the fluid will now be in the tubes.)

- Get back in the plane and start pumping the hand brake and toes brakes alternately while watching the fluid in the tubing.  Do this until you no longer see any air bubbles in the tubes.

- When the tubes run clear with fluid (no air) the system should be well bled.

- Close the bleed screws.

- Using a jar (or something) to capture the loose fluid, remove the tubing from the resevoir first.  Have the tubes drain into your jar.

----IMPORTANT---- DO NOT Remove the tubing from the bleed screws while the other ends are still in the resevoir.  If you do, they will syphon all the fluid out of the resevoir and you will have to repeat this whole thing all over again.  (Ask me how I know ;-)  ).

- Remove the other ends of the tubes form the bleed screw and raise them above the level of the ends draining into your jar to avoid spilage onto the ground.


I read about this technique on this site first about 4 years ago, but I could not locate the thread for you.  That said, it works really well and it's fast.  Good luck, and let us know how it works.

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Re: Seneca - brake bleeding - HELP!

Take a tip from the Piper Service Manual, unhook the toe cylinders from one end and tip them up to purge the air from them while bleeding.

PITA, but you'll get there.

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Re: Seneca - brake bleeding - HELP!

Run Clear tubing from all bleeders at both wheels at same time to a tee above reservoir and the center of the tee into res cap tube. Fill all tubes and res. Two people pump all four pedals all at same time - 4 down, 4 up, until no bubbles in tubing. Start pumping the hand brake first to make sure it's fully bled,10 pumps, then the pedals.

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Re: Seneca - brake bleeding - HELP!

Run clear tubing from all bleeders at both wheels at same time to a tee above reservoir and the center of the tee into res cap tube. Fill all tubes and res. (5606 hydraulic fluid is not good to drink when you suck tubes to fill them from can)  Two people pump all four pedals all at same time - 4 down, 4 up, until no bubbles in tubing from wheels. Start pumping the hand brake first to make sure it's fully bled,10 pumps, then the pedals.

720 252 3912 Walt Wills A&P, IA, CFII, MEL 30 years in Aviation
In GOD's Lap Aviation aircraft Maintenence
Front Range Airport FTG
Denver (Watkins) Colo

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Re: Seneca - brake bleeding - HELP!

Not all Pipers have the hand brake or a reservoir cap tube, but the method of pumping all pedals at same time still applies if master cylinders are tied  (plumbed) together. Pump the hand brake first if the airplane has a hand brake master cylinder. 
The Senecas have a pull handle hand brake which holds the fluid
pressure after foot braking is applied.
You can have someone hold the tee discharge into the res or hold it some other way.

Walt, In GOD's Lap FTG

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Re: Seneca - brake bleeding - HELP!

Make certain that you are not missing the 3/16inch spacer on the axle of the affected wheel.  This is the spacer that goes between the wheel and trunion.  If it is missing, it will give the same symptoms as air in the brake line.

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Re: Seneca - brake bleeding - HELP!

If the above doesn't work, and if you're asking because the brakes have gotten progressively weaker, check the thickness of the brake discs. If the discs are worn under size, you may spend days trying to bleed them - and not be successful.

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Re: Seneca - brake bleeding - HELP!

As the owner of a Seneca II I had the same problem. The only way I foud to remedy the problem was to remove the cylinders on both the toe brakes and the hand brake, replace the seals and fill with fluid mil-h-5606 prior to reinstalling them. This was the only way that would work for me even after reverse bleeding wouldnt remove air from the cylinders.

C Collum A&P, Pvt Pilot

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