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I've got an odd behavior in my '78 J that's causing a lot of head scratching at the moment.  My left brake will gradually start to drag, and eventually lock up when taxiing, especially during long taxis.  Even when only using the right brake, the left one will start to drag, and progressively get worse.  If you let the plane sit for 1/2 hour, it frees up.  My A&P checked the calipers (they were free), and the master cylinder (no sign of problems).  I'm very careful not to ride the brakes.  With the plane in the hangar I've been able to move the plane freely.  Hop in and just tap the brakes, and then the left starts to drag.  I'm trying to avoid a shotgun approach to fixing this, but don't have any ideas on what to check next.  Any thoughts from the MS crowd?

Tom

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You tap the brakes... and the problem begins... How far back do you want to look?

why is the mechanic not pointing to the problem?

What would cause the progressive getting worse?

sounds like temperature is the only thing changing. That is pretty local.

what allows the brakes to reset, after they have been used? Also very local.

Sounds like dirty or worn guides are not allowing the pads to open after they clamped shut...

Somewhat unusable until you get this cleaned up...

See if @M20Doc has some insight...

 

PP thoughts only, not a mechanic...

 

Best regards,

a

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Are the rotors warped?  Do the rotors drag and/or make an uneven sound when you rotate the wheel by hand?  A sufficiently warped rotor would drag a little bit when cold, but the problem could worsen as the dragging produces more heat until it eventually binds somewhere

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jack it up and spin the wheel.   Change the fluid.

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39 minutes ago, LANCECASPER said:

Have the brakes been bled recently? The brake fluid gets dark and thick with age and heat

No, I don't think they've been bled in quite some time.  I purchased the plane in August, and it hasn't flown a lot lately.

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30 minutes ago, jaylw314 said:

Are the rotors warped?  Do the rotors drag and/or make an uneven sound when you rotate the wheel by hand?  A sufficiently warped rotor would drag a little bit when cold, but the problem could worsen as the dragging produces more heat until it eventually binds somewhere

No signs of warped rotors; smooth action when braking, even when you don't want it!

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45 minutes ago, carusoam said:

You tap the brakes... and the problem begins... How far back do you want to look?

why is the mechanic not pointing to the problem?

What would cause the progressive getting worse?

sounds like temperature is the only thing changing. That is pretty local.

what allows the brakes to reset, after they have been used? Also very local.

Sounds like dirty or worn guides are not allowing the pads to open after they clamped shut...

Somewhat unusable until you get this cleaned up...

See if @M20Doc has some insight...

 

PP thoughts only, not a mechanic...

 

Best regards,

a

Yes, I don't like landing and only being able to use the right brakes!  Mechanic said guides were clean and not binding.  I get the feeling these are not very complicated systems, so this should be a simple fix. 

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Drain the fluid because you can...

Expect the fluid to be really dark red... and gloppy...

check your logs to see how old the fluid is...

know where the reservoir is?  Got access panels above the cowl...?

avoid letting air getting into the system...

Best regards,

-a-

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To set the parking brake, the brakes have to be held down first...

the parking brake will hold that pressure in the system...

having some air in the system is going to account for some added interesting behavior...

-a-

 

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Another thing to look at is the caliper itself. The piston will gum up after time with old fluid. That could cause it not to release and stick but free up later. Might be worth disassembling the caliper and cleaning the internals then refill with fresh fluid and bleed like others have mentioned here.

I found mine quite gummy inside a few years back when I replaced all my flexible hoses in the hydraulic system.

David

Edited by Sabremech
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Again these aren’t complicated systems. The most you’re going to change is fluid and o rings most likely.  

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Sounds like either moisture or air in the caliper: either one will expand with heat and put the brake on, thus generating more heat and eventually locking the brake.  Expect also to see a warped rotor generating the initial heat that starts the cycle.  Alternate source of initial heat could be sticking caliper sliders, causing one pad to always be at least partially engaged.

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Old hydraulic brake fluid will turn to thick syrup over time.  I would connect a pressure bleeder pot to the top fitting of the reservoir, pump it up to 25-30 psi then open the caliper bleeder screws one at a time until fresh thin red fluid comes out, close the bleeder screw then repeat for the opposite side.

Clarence 

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5 hours ago, Nippernaper said:

 I get the feeling these are not very complicated systems, so this should be a simple fix. 

One of the easiest maintenance tasks on the plane is changing the pads.   3 tools and 15 minutes per side.   Bleeding is one of the harder.  Using a oil can from the bottom and 20 to 40 pumps should get the air out.

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I had a similar issue and it was the slave cylinder (the puck that presses on the brake lining)... a little corrosion and it wanted to stick 'on'.

Easy enough to disassemble, clean up, re-install, bleed...I believe new o-rings were needed.

Edited by Immelman

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Had the same thing happen to me. That hydraulic fluid came out like jello. Just take 15 minutes to bleed it  

-Robert

Edited by RobertGary1

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17 hours ago, M20Doc said:

Old hydraulic brake fluid will turn to thick syrup over time.  I would connect a pressure bleeder pot to the top fitting of the reservoir, pump it up to 25-30 psi then open the caliper bleeder screws one at a time until fresh thin red fluid comes out, close the bleeder screw then repeat for the opposite side.

Clarence 

pressure bleeders are a life saver - I just finished rebuilding the calipers on an '84 Honda Sabre someone gifted me as a project bike... 3 hours of manual bleeding later, and all the air still isn't out of it...  finally broke down and ordered a syringe bleeder (along with new steel lines for it), because my hand can't take another thousand pumps on the lever...

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these brakes are rather unusual. For the love of man dont ever let the system run dry or drain out. After spending perhaps 30 hours bleeding brakes, they are almost normal.

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I just laugh when I read stories of people trying to get the air out of their mountain brake lines.....    I have run mechanical disc since 2000

 

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I had the same issue on my karmann ghia. The brake line had collapsed internally and didn't let the brake pressure blead off normally. So it was fine after sitting a while, but once you started using the brakes they would drag and heat up. The fluid was like syrup and I had to force out a bunch of gunk with a vacuum pump and replace the soft brake lines. Bleading is a whole other story. Secret is to perform the correct magic rituals or have the right equipment. Like hot starting an io-360.

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On 10/9/2018 at 2:07 PM, LANCECASPER said:

Have the brakes been bled recently? The brake fluid gets dark and thick with age and heat

Replacing my brake fluid fixed a brake problem I had which seemed to just not be working as well.  It had gotten very thick over the years.  It took MANY hours and many flush/bleeding to get the old fluid out. 

Separately, my spouse's car had an issue with a caliper that was not fully resetting - it's a common bad design in her vehicle. 

You may need a new caliper or to clean the area around the caliper as mentioned to allow it to fully retract.

 

-Seth

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