Braking After Landing

[Andy95W]

53 minutes ago, 320KPH said:

. Fresh brake fluid is clear in colour.

Fresh brake fluid for our airplanes is a bright red color (MIL-H-5606A)

Everything else @320KPH said is right on and very good information.

[RobertGary1]

Yea as a Mooney owner who fly’s lots of other brands Mooney brakes are not what you get from most other brands. 

I’ve  never seen old fluid cause that issue. A flush is needed when the brakes release slowly. At annual you’ll see the pads as they have to come out when you remove the wheel. 

Most likely it’s just par for the course  

-Robert

Edited June 20, 2018 by RobertGary1

[jaylw314]

1 hour ago, 320KPH said:

Brake fluid is hygroscopic, it absorbs moisture fom the air and when the fluid is compressed the moisture can boil off, reducing pressure applied to the calipers. On motorcycles brake fluid is recommended to be changed annually.

Old brake fluid could therefore result in 'spongy" brakes and ineffective braking.

Flushing the system is recommended, rather than merely bleeding the brakes.

A vacuum pump system is available from auto supply shops for 'reveerse bleeding your brakes. with one of thes pumps bleeding or flushing brakes can be a one man operation.

If your brake fluid is discouloured, dark brown, your fluid is really old. Fresh brake fluid is clear in colour.

Conversely, it's hard to imagine a scenario where old brake fluid would get hot enough for long enough to boil off moisture.  At worst, we might stand on the brakes for what, 10 seconds?  The rotor will get hot, but I can't imagine there's enough time for the fluid to heat up in that time.  Afterwards, sure the brake fluid might heat up enough to get water vapor bubbles, but by that time you're taxiing.  It's not like automobile brakes where you might be standing on the brakes multiple times in a row.

Old fluid might cause corrosion from the absorbed moisture, but I can't imagine it would realistically affect braking performance.

[RobertGary1]

They should be pressure bled from the bottom up. 

 

-Robert

Edited June 20, 2018 by RobertGary1

[RobertGary1]

1 hour ago, jaylw314 said:

Conversely, it's hard to imagine a scenario where old brake fluid would get hot enough for long enough to boil off moisture.  At worst, we might stand on the brakes for what, 10 seconds?  The rotor will get hot, but I can't imagine there's enough time for the fluid to heat up in that time.  Afterwards, sure the brake fluid might heat up enough to get water vapor bubbles, but by that time you're taxiing.  It's not like automobile brakes where you might be standing on the brakes multiple times in a row.

Old fluid might cause corrosion from the absorbed moisture, but I can't imagine it would realistically affect braking performance.

In practice old brake fluid just tends to just become jelly like in aircraft. When you bleed it out you can squish it in your hand  

youre right that it’s not the same type of fluid or environment as a motorcycle 

-Robert

Edited June 20, 2018 by RobertGary1

[Guest]

1 hour ago, RobertGary1 said:

They should be pressure bled from the bottom up. 

 

-Robert

But if you’re trying to displace old fluid, why not pump it out the bottom?  It’s way closer to the bleeder port than the reservoir.

Clarence

[RobertGary1]

1 hour ago, M20Doc said:

But if you’re trying to displace old fluid, why not pump it out the bottom?  It’s way closer to the bleeder port than the reservoir.

Clarence

If there was also any air in the caliper you’re not likely to get it from a suction bleed at the bottom 

I suppose if there is no concern for any air then it doesn’t really matter  

-Robert 

Edited June 20, 2018 by RobertGary1

[Guest]

1 hour ago, RobertGary1 said:

If there was also any air in the caliper you’re not likely to get it from a suction bleed at the bottom 

I suppose if there is no concern for any air then it doesn’t really matter  

-Robert 

Assuming that the issue with sluggish brakes is gelled fluid in the hot part of the system(the caliper) then simply pumping fluid from the reservoir through the master cylinders and out the bleeder at the caliper would be the shortest method of displacing gelled fluid with fresh fluid.  Done it more than a few times.

Clarence

[DonMuncy]

3 minutes ago, M20Doc said:

Assuming that the issue with sluggish brakes is gelled fluid in the hot part of the system(the caliper) then simply pumping fluid from the reservoir through the master cylinders and out the bleeder at the caliper would be the shortest method of displacing gelled fluid with fresh fluid.  Done it more than a few times.

Clarence

I assume if you find a spongy brake, you would conclude likely air in the line, and you would not do it that way.

[Guest]

3 minutes ago, DonMuncy said:

I assume if you find a spongy brake, you would conclude likely air in the line, and you would not do it that way.

Correct, then it would require bleeding.

Clarence

[Tom 4536]

Thanks for all the input. I definitely can't lock up the brakes. They do hold just fine during the runup.

[steingar]

I bet my M20c has the same brakes at the OP’s F and the same as the newer aircraft. If I’m right, what works fine for me will be less effective for a heavier airplane, and even less so for the newer ones. Same amount of braking power for more mass.

[320KPH]

I really am surprised that the fluid in some of these birds is solidifying. how old must the brake fluid be?

If the moisture in the fluid leads to corrosion in the caliper cylinders, the pistons would take more force to move and may end up either not working effectively or nnot retracting properly, which I knew of in one Mooney thereby locking the brakes.  Conversely the master cylinders may be obstructed or contaminated making it difficult to apply full braking pressure.

The discs on the Mooney are relatively small compared to a motorcyc;le brake disc, and there is a lot of friction built up stopping 2500 lbs worth of metal moving at 60 mph. Someone with a slide rule could probably work out how much heat is generated ( let me point out here that I realise that you don't just hit the runway and stand on the brakes)

If the brakes initially bite, THEN go spongy, this would be the symptom indicating old fluid boiling off.

If the fluid is not changed in ten years, I suspect it would be goop in the system preventing the brakes from working effectively.

Edited June 22, 2018 by 320KPH
corrected landing weight

[neilpilot]

58 minutes ago, 320KPH said:

If the fluid is not changed in ten years, I suspect it would be goop in the system preventing the brakes from working effectively.

^^^ This

[Bartman]

In 2008 my parking brake did not work. They flushed congealed fluid out of the system and the parking brake worked but it rarely gets used. Checked it this week and no longer holds.  Plan on flush the brake system again next oil change.  10 years it is. 

[Bartman]

So if this is a well known issue with Mooney brakes, is there a Service Bulletin ?

And why are we still using fluid known to degrade ?  Never heard of congealed brake fluid in an automobile. 

[steingar]

6 minutes ago, Bartman said:

So if this is a well known issue with Mooney brakes, is there a Service Bulletin ?

And why are we still using fluid known to degrade ?  Never heard of congealed brake fluid in an automobile. 

Most cars aren't on the road as for the length of time we keep aircraft around.

[Hank]

55 minutes ago, steingar said:

Most cars aren't on the road as for the length of time we keep aircraft around.

All of my cars are . . . . Always have been. I've only ever replaced one at single-digit age, and that was my first one after college. Are you saying that at some point I should flush and replace the brake fluid in my 1992 convertible?  They still work just fine.

[MyNameIsNobody]

3 hours ago, Bartman said:

In 2008 my parking brake did not work. They flushed congealed fluid out of the system and the parking brake worked but it rarely gets used. Checked it this week and no longer holds.  Plan on flush the brake system again next oil change.  10 years it is. 

I use my parking brake all the time during the run-up.  Beats standing on the brakes.

[steingar]

4 hours ago, Hank said:

All of my cars are . . . . Always have been. I've only ever replaced one at single-digit age, and that was my first one after college. Are you saying that at some point I should flush and replace the brake fluid in my 1992 convertible?  They still work just fine.

You have any 1962 model year cars around?  

[Hank]

1 minute ago, steingar said:

You have any 1962 model year cars around?  

Nope. But people here are saying to change the brake fluid in cars and planes every few years. I don't spend money for the sake of spending it, and try not to fix things that aren't already broken or giving indications that they may break. The brakes in my cars ans Mooney work just fine. I probably use the emergency brake in my truck every month or two (but used it parking in my driveway in WV), but have yet to use the parking brake in my Mooney in the eleven years that I've owned her.

[steingar]

Just now, Hank said:

Nope. But people here are saying to change the brake fluid in cars and planes every few years. I don't spend money for the sake of spending it, and try not to fix things that aren't already broken or giving indications that they may break. The brakes in my cars ans Mooney work just fine. I probably use the emergency brake in my truck every month or two (but used it parking in my driveway in WV), but have yet to use the parking brake in my Mooney in the eleven years that I've owned her.

I've owned all of my cars for a minimum ten years, and the minimum was just because I totaled the poor thing.  Average is closer to 14.  I've never bled the brakes on any of them nor have I had them bled, and yes they all worked fine.  I did bleed the brakes on my 1983 Goldwing, and boy did they need bled.  I own my bikes for an average of 10 years, and I've never had to bleed them either.  I used to because it was recommended, but never saw one that really needed it except the wing.

I don't use the parking brake in the Mooney, I'm always afraid I'll forget to undue it and try and take off with it on.  My cars have always been and will always be manual, so I use the emergency brake all the time.

[kortopates]

I bet my M20c has the same brakes at the OP’s F and the same as the newer aircraft. If I’m right, what works fine for me will be less effective for a heavier airplane, and even less so for the newer ones. Same amount of braking power for more mass.

You'd bet wrong. There was more than one version of single pick brakes used between your C and the midbody. The long bodies and Encore use a double puck brake. However, this doesn't improve braking action like you might think. It mainly improves how long the pads last. Same tires with same contact area, albeit more weight.


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[jaylw314]

7 minutes ago, kortopates said:

You'd bet wrong. There was more than one version of single pick brakes used between your C and the midbody. The long bodies and Encore use a double puck brake. However, this doesn't improve braking action like you might think. It mainly improves how long the pads last. Same tires with same contact area, albeit more weight.

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Also reduces how hot the brakes can get (more surface area)

[steingar]

15 hours ago, kortopates said:

You'd bet wrong. There was more than one version of single pick brakes used between your C and the midbody. The long bodies and Encore use a double puck brake. However, this doesn't improve braking action like you might think. It mainly improves how long the pads last. Same tires with same contact area, albeit more weight.

Same frictional area, more weight. The burden of being frequently correct is a heavy one.