Brake Bleeding problem

H. Paul Shuch is a Light Sport Repairman with Maintenance ratings for airplanes, gliders, weight shift control, and powered parachutes, as well as an independent Rotax Maintenance Technician at the Heavy Maintenance level. He holds a PhD in Air Transportation Engineering from the University of California, and serves as Director of Maintenance for AvSport of Lock Haven.

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BrianL99
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Brake Bleeding problem

Postby BrianL99 » Sat May 07, 2016 5:12 pm

My airplane has been in the shop way too long and we still can't seem to get the brakes bled.

I have a Sting Sport, with brakes only on the Pilot side and it has an emergency brake.

We've tried applying pressure through the Reservoir and bleeding conventionally.

We'd tried applying pressure through the reservoir and suction to the bleeder.

We've replaced the Master Cylinders twice. It's a dual brake system, operating off one reservoir.

We've drained all fluid and re-filled with pressure from the brake caliper, forward. The reservoir fills, but we still have air bubbles.

The emergency brake is a simple "on/off toggle switch" on the brake line. If the emergency brake is ON, we have full braking. As soon as we release the emergency brake, we have a squishy pedal. This leads us to believe there's some "leakage", forward of the emergency brake toggle ... but we surely can't find it.

Help !

3Dreaming
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Re: Brake Bleeding problem

Postby 3Dreaming » Sat May 07, 2016 9:36 pm

Some brake systems are easy to bleed, and others not so much. For example, Piper Cherokee brakes can be real hard to get the air out of, especially with 5 master cylinders. Sometimes the cylinders on the pedals can trap air inn the top of the cylinder. On those you have to have the cylinder lying flat when pumping fluid through from the wheel cylinder.

Something else that could be going on is a bad line that is expanding when you apply pressure.

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FastEddieB
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Re: Brake Bleeding problem

Postby FastEddieB » Sun May 08, 2016 6:42 am

Possibly not relevant here, but...

On motorcycles, I have found it helps to have the caliper pistons pushed all the way back into their bores. It seems that in some installations air in the caliper can be hard to bleed.

It may be wise to clean the exposed portion of the pistons first. Otherwise the grungy parts could possibly damage seals.

Suction to the bleeder works well, but I see you've tried that. Pushing fluid in through the bleeder also works.

Good luck - I know how frustrating it can be.
Fast Eddie B.
Sky Arrow 600 E-LSA • N467SA
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roger lee
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Re: Brake Bleeding problem

Postby roger lee » Sun May 08, 2016 8:08 am

Whose brakes are they. There are different ways to bleed some brakes. The most common for most brake systems is from the bottom up. There are a couple of brake systems out there that take a special procedure and there is no written documentation to do it. The Gobosh is one of them.

Most systems should be bled from the nipple on the bottom of the caliper. The fluid is then pressurized up through the system into the reservoir.
The best and cheapest tool to do this can be had from Ace hardware. It is a 1 gal. pump up bug sprayer. Take off the front nozzle and just slide on some tubing. Pour the fluid in the pump, pump it up and attach the tube to the bottom of the caliper nipple. Then open the nipple on the caliper a couple of turns, press the trigger on the pump and the high speed fluid flow will flush out all air and charge the syste, Put an empty water bottle with a tube on it up on the reservior to catch the over flow. I usually waste maybe 1 ounce. The high speed flush carries air out. Using a slow hand operated oil can is too slow and many times leaves air in the system. The Ace pump is a bout $10 and well worth the money. I can bleed brakes in a few minutes this way. Give me an email address and I can send you a couple of pictures.

let me know whose brakes they are and I may be able to help.
Roger Lee
Tucson, Az.
LSRM-A, Rotax Instructor & Rotax IRC
(520) 574-1080 (Home) Try Home First.
(520) 349-7056 (Cell)

BrianL99
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Re: Brake Bleeding problem

Postby BrianL99 » Sun May 08, 2016 8:18 am

roger lee wrote:Whose brakes are they. There are different ways to bleed some brakes. The most common for most brake systems is from the bottom up. There are a couple of brake systems out there that take a special procedure and there is no written documentation to do it. The Gobosh is one of them.

Most systems should be bled from the nipple on the bottom of the caliper. The fluid is then pressurized up through the system into the reservoir.
The best and cheapest tool to do this can be had from Ace hardware. It is a 1 gal. pump up bug sprayer. Take off the front nozzle and just slide on some tubing. Pour the fluid in the pump, pump it up and attach the tube to the bottom of the caliper nipple. Then open the nipple on the caliper a couple of turns, press the trigger on the pump and the high speed fluid flow will flush out all air and charge the syste, Put an empty water bottle with a tube on it up on the reservior to catch the over flow. I usually waste maybe 1 ounce. The high speed flush carries air out. Using a slow hand operated oil can is too slow and many times leaves air in the system. The Ace pump is a bout $10 and well worth the money. I can bleed brakes in a few minutes this way. Give me an email address and I can send you a couple of pictures.

let me know whose brakes they are and I may be able to help.


That's pretty much what we've tried Roger, but using a "hand operated pump can". Perhaps we didn't get the brake fluid pushing through fast enough? I'll have to pick up a bug sprayer this morning.

I fly a TL Ultralight Sting, but I'm not sure who makes the brake system.

Thanks!

roger lee
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Re: Brake Bleeding problem

Postby roger lee » Sun May 08, 2016 12:19 pm

I'm sitting at a yard sale right now. I'll try and post some pictures a little later. If you have any questions call me. The little hand pumps don't do very well for getting air out. To slow and the fluid just goes around the air instead of forcing flushing it out.
Roger Lee
Tucson, Az.
LSRM-A, Rotax Instructor & Rotax IRC
(520) 574-1080 (Home) Try Home First.
(520) 349-7056 (Cell)

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FastEddieB
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Re: Brake Bleeding problem

Postby FastEddieB » Sun May 08, 2016 3:16 pm

Harbor Freight sells a "Pittsburgh" brand bleeder, that sucks from the bleeder. About $35 but needs an air source.

Made short work of a rear brake line on a BMW motorcycle that I could not get bled any other way.

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Fast Eddie B.

Sky Arrow 600 E-LSA • N467SA

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BrianL99
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Re: Brake Bleeding problem

Postby BrianL99 » Sun May 08, 2016 6:57 pm

Who ever thought brake bleeding could be such an adventure!

Thanks for all the advice guys, we'll try again this week.

roger lee
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Re: Brake Bleeding problem

Postby roger lee » Mon May 09, 2016 8:22 am

Brake flush pump. Best thing ever and easy to use and works like a charm for about $10
Attachments
Brake Flush 002.jpg
Brake Flush 002.jpg (212.1 KiB) Viewed 1858 times
Brake Flush 001.jpg
Brake Flush 001.jpg (204 KiB) Viewed 1858 times
Roger Lee
Tucson, Az.
LSRM-A, Rotax Instructor & Rotax IRC
(520) 574-1080 (Home) Try Home First.
(520) 349-7056 (Cell)

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drseti
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Re: Brake Bleeding problem

Postby drseti » Mon May 09, 2016 8:46 pm

FastEddieB wrote:Harbor Freight sells a "Pittsburgh" brand bleeder, that sucks from the bleeder. About $35 but needs an air source.


Thanks, Eddie. Just bought one. $27.99 with the customary 20% off coupon.
The opinions posted are those of one CFI, and do not necessarily represent the FAA or its lawyers.
Prof. H. Paul Shuch, Ph.D., CFII, LSRM-A/GL/WS/PPC, iRMT
AvSport of Lock Haven
fly@AvSport.org
http://AvSport.org
http://facebook.com/SportFlying

roger lee
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Re: Brake Bleeding problem

Postby roger lee » Tue May 10, 2016 8:22 am

I don't think you'll find a suction style bleeder to work as well as a pressure bleeder.

First you'll have to keep an eye on the reservoir and air wants to go to the high points so as the fluid is sucked downward air still wants to travel upward. The slower suction type bleeder won't move the fluid fast enough to make the procedure efficient or quick. The suction type bleeder is for more specific applications. I think you may find it more difficult. I have tried them and they are frustrating to get a good job in any decent time frame. Our brake systems were meant to be flushed from the bottom up. You'll also need more equipment. All I need is the pump and a empty water bottle and it doesn't leave a mess.

Here is a test. I can bleed both calipers on a plane with my pump in about 15 min. total and never have any air bubbles. I only waste about 1 oz. of fluid and the reservoir is always full and you'll never have to watch it to make sure you don't have a low level.
Roger Lee
Tucson, Az.
LSRM-A, Rotax Instructor & Rotax IRC
(520) 574-1080 (Home) Try Home First.
(520) 349-7056 (Cell)

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FastEddieB
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Re: Brake Bleeding problem

Postby FastEddieB » Tue May 10, 2016 1:31 pm

roger lee wrote:I don't think you'll find a suction style bleeder to work as well as a pressure bleeder.

...The suction type bleeder is for more specific applications.


I think the key is there is no "one size fits all".

The couple of times I've needed to bleed the brakes on the Sky Arrow, feeding the fluid in through the caliper bleeder screw worked just fine. All I had handy was a medium syringe, but it got the job done.

But as I've said, it seems some pockets of air in some systems resist that method. At that point sometimes a suction bleeder can make all the difference.

Can't hurt to have both systems available for that one time one's "normal" way just isn't getting the job done!
Fast Eddie B.

Sky Arrow 600 E-LSA • N467SA

FastEddieB@mac.com

BrianL99
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Re: Brake Bleeding problem

Postby BrianL99 » Wed May 11, 2016 6:36 am

So we tried Roger's methodology yesterday ... semi-successful.

After about 20 minutes of pumping fluid up from the brake caliper, we took out the seat to trace the brake line.

Under the Pilots seats, we found a "hump" in the brake line, that routed the line up & over the wing spar ... that "hump" was full of tiny bubbles.

We temporarily re-routed the line and were able to get out "most" of the bubbles ... we still have some, we can't get to move through the system.

We even tried to bore out an old fitting to use on the caliper, so we could generate more pressure, but weren't successful with that.

So as of yesterday (haven't checked today), I have reasonable brakes, with some tiny bubbles in the lines.

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FastEddieB
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Re: Brake Bleeding problem

Postby FastEddieB » Wed May 11, 2016 7:37 am

Brian,

Again, maybe try that Harbor Freight item. I worked for hours on that BMW and could not get all the air bubbles out. The suction bleeder sucked out a large amount of air bubbles, large and small, and within 10 or 15 seconds was pulling nothing but fluid.
Fast Eddie B.

Sky Arrow 600 E-LSA • N467SA

FastEddieB@mac.com

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drseti
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Re: Brake Bleeding problem

Postby drseti » Wed May 11, 2016 7:59 am

Tom is right that pressure bleeding from the bottom up generally works best - but there are exceptions. So, I'm with Eddie that the suction method is worth a try.
The opinions posted are those of one CFI, and do not necessarily represent the FAA or its lawyers.
Prof. H. Paul Shuch, Ph.D., CFII, LSRM-A/GL/WS/PPC, iRMT
AvSport of Lock Haven
fly@AvSport.org
http://AvSport.org
http://facebook.com/SportFlying


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