chronically dragging brakes

GeorgeC

GeorgeC

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GeorgeC
Shortly after purchasing my plane in 2018, on a couple of occasions, my brakes would drag when taxiing after landing. I had them serviced and that cleared things up for a while. At annual a couple of months ago, they found that the plates were not floating properly on the guide pins, so they serviced them again. Since then, I've been lubing the pins periodically with dry moly spray.

Yesterday, the left side started grabbing on me again and got quite hot by the time I made it to my tiedown.

Is it time to start throwing parts at it?
 

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Who is the brake manufacturer? I had the same issue with the MATCOs that came on my plane. Once I switched everything over to Beringers, problem solved.
 
GeorgeC said:
my brakes would drag, they found that the plates were not floating properly on the guide pins, I've been lubing the pins periodically with dry moly spray.
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Not an A&P but have a fair bit of experience with automotive brakes. Not familiar with dry moly, for lubricating brake pins I use https://www.amazon.com/AGS-BK8-Brak...FL7EDS/ref=sr_1_1?crid=2CXV6PTLQXF92&dchild=1
Typically when brakes drag either the caliper is due for replacement or there is corrosion on the hardware.
Do the plates have good clearance and feel free?
 
Prior to my first annual, they cleaned the cylinders and pistons and replaced the orings.
At the second annual, "removed rust from [caliper pins] and rust from mounting bracket holes. lubricated and reinstalled".

Mine's not the only Cessna without wheelpants that lives outside, and the plane gets flown weekly.
 
Do you have the insulators installed (#18 in the diagram)? Are they in good shape? Omitting those will cause the brakes to drag. Not all Cleveland calipers require the insulators so it isn't uncommon for a mechanic to overlook them.
 
Personally, I would pull the wheels (Part 43, appendix A, C, 1) and play with the calipers. I would not be surprised if the answer was reasonably obvious - what slides easily, and what sticks. Are the pads wearing evenly...

But, I ain't no A&P.
 
After all that cleaning of corrosion on the pins and the holes on the torque plate, I would have to wonder if there isn't enough slop that the brake caliper can cock a bit, causing them to hang up at times.
 
Quite possibly None of the above.

The Cleveland master cylinders on a Cessna have a check valve in them that is supposed to open when the brakes are released and the master's piston hits the retracted stop. There are two springs in the master, the small one that forces the valve closed when the piston starts moving downward, and the large one that pushes the pushrod/piston nut back up on release. That large spring gets tired with age and loses its push, and it often won't push hard enough to force the valve open against the force of the little closing spring. Fluid remains trapped in the syem, and when the caliper gets warm from braking, the pressure builds enough to make the brake drag. You can fool all you want with the caliper assembly and get absolutely nowhere with this.

The diagnosis is to taxi and brake and get it warm and see if it will start dragging. If it does, stop and shut down and jump out and try to push the airplane. It will be hard. Then crack open the bleeder valve on the caliper and see if a bit of fluid squirts out. Close it and try to push the airplane again. It will likely move easily. The master is trapping fluid when it's not supposed to.

The manual needs to be consulted when servicing these things. There are specific things that are important, and that big spring must be installed correctly. Installers have been known to invert them, and now you have trouble.

Later versions didn't have that valve. The piston rose right out of the cylinder just enough that pressure couldn't be trapped.

upload_2020-5-3_10-41-51.png
 
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As ever, thanks everyone. Given the recent caliper mx, a local A&P suggested also suggested looking at the master cylinder springs/valves.

Do the flex lines have a practical calendar life? Every other piece of rubber I've encountered so far has been cracked.
 
Not sure if certified specs a particular fluid for brakes, but draggy brakes (hot) + possibly cracking lines is a recipe for a fire. I have converted to Royco 782 in my brakes and gear to lessen the possibility of a fire. Might research it and what you are currently using if you end up changing lines.
 
Hydraulic lines typically run on-condition. If they're not seeping or hardened like wood or the steel braid exposed and rusting they're usually ok. They should have a stainless data band on them with the manufacturing date. If they're 20 years old I'd replace them. The ones at the master cylinders are likely as old as the airplane. So often I've found stuff under the rudder bar covers that tells me that they haven't been off in decades. So how does one comply with "inspect all systems" if they aren't looking in there?
 
FORANE said:
Not sure if certified specs a particular fluid for brakes, but draggy brakes (hot) + possibly cracking lines is a recipe for a fire. I have converted to Royco 782 in my brakes and gear to lessen the possibility of a fire. Might research it and what you are currently using if you end up changing lines.
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The manufacturers specify MIL5606 fluid. That's Royco 756. Substituting anything else for 5606 is asking for legal trouble if nothing else. If there is no guarantee of compatibility you're on your own.
 
Dan Thomas said:
The manufacturers specify MIL5606 fluid. That's Royco 756. Substituting anything else for 5606 is asking for legal trouble if nothing else. If there is no guarantee of compatibility you're on your own.
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seems like a good example of what's wrong with the certified world.
 
Dan Thomas said:
Substituting anything else for 5606...
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FWIW: MIL-PRF-5606 and MIL-PRF-83282 are considered compatible. The main difference is 83282 is limited on the cold side and not as popular in GA so not all FBOs may have it if you need it. That's one reason some people don't switch over. To the best of my knowledge Cessna and Piper do not offer any guidance on switching to 83282. But there are other acceptable guidance sources that allow it. Here are a couple, but for some reason I couldn't get any links to work.
AC 43.13-1B, Para. 9-27(b):
"MIL-H-83282 is significantly more flame resistant than MIL-H-5606, but a disadvantage is the high viscosity at low temperature. It is generally limited to -40 �F. However, it can be used in the same system and with the same seals, gaskets, and hoses as MIL-H-5606."

Cleveland Technicians Service Guide, AWBTSG0001-21, Page 21:
"Hydraulic Applications - Use fluids compatible with the systemMIL-H-5606 / MIL-H-83282 (Red Oils)"

There were also several ADs issued for various reasons which required the change from 5606 to 83282 and per the AD it was a simple flush of the 5606 and re-service with 83282 fluid. It was through a helicopter AD that I learned of the compatibility. Considering an AD is "approved" data that pretty much backs up the above acceptable guidance. However, I only helped 2 people convert to 83282 in their aircraft as 83282 wasn't readily available unless they carried a can or two on board. Most didn't consider the fire danger issue enough to convert from 5606 on their little puddle jumpers.
 
Bell206 said:
FWIW: MIL-PRF-5606 and MIL-PRF-83282 are considered compatible. The main difference is 83282 is limited on the cold side and not as popular in GA so not all FBOs may have it if you need it. That's one reason some people don't switch over. To the best of my knowledge Cessna and Piper do not offer any guidance on switching to 83282. But there are other acceptable guidance sources that allow it. Here are a couple, but for some reason I couldn't get any links to work.
AC 43.13-1B, Para. 9-27(b):
"MIL-H-83282 is significantly more flame resistant than MIL-H-5606, but a disadvantage is the high viscosity at low temperature. It is generally limited to -40 �F. However, it can be used in the same system and with the same seals, gaskets, and hoses as MIL-H-5606."

Cleveland Technicians Service Guide, AWBTSG0001-21, Page 21:
"Hydraulic Applications - Use fluids compatible with the systemMIL-H-5606 / MIL-H-83282 (Red Oils)"

There were also several ADs issued for various reasons which required the change from 5606 to 83282 and per the AD it was a simple flush of the 5606 and re-service with 83282 fluid. It was through a helicopter AD that I learned of the compatibility. Considering an AD is "approved" data that pretty much backs up the above acceptable guidance. However, I only helped 2 people convert to 83282 in their aircraft as 83282 wasn't readily available unless they carried a can or two on board. Most didn't consider the fire danger issue enough to convert from 5606 on their little puddle jumpers.
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Good enough for me. Thanks.
 
FORANE said:
seems like a good example of what's wrong with the certified world.
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Well, there have to be limits, or people would use DOT3 automobile brake fluid in their airplanes and trash the entire system in an hour. There are countless ways that you can wreck something or increase the flight risks by making changes that look innocent. And people keep doing such things, so the regulators keep making more rules. Wrapping more chains around us all just because a few won't behave.

Earlier in my working life I was a shop foreman and staff instructor in a heavy duty brake component rebuilding plant. Air brake valves, actuators and compressors. Hydraulic brake master and boosters, both vacuum- and hydraulically boosted. We were kept plenty busy rebuilding the hydraulic stuff ruined when folks put motor oil in the brake reservoirs. The air brake stuff suffered mostly from dirt, either sucked in by the compressor through filters that should have been inspected or changed long before, or through the tractor/trailer gladhand couplers that were just dropped in the dirt once disconnected. That dirt would get blown throughout the entire system during the constant pressure/release of air. A compressor's life was measured in minutes once it started sucking in the clouds of dust at a construction site on on a logging road.

And at least half of it had nothing wrong with it at all. Nothing. Troubleshooting was a rare skill in that industry, too. Start throwing parts at the problem until it goes away.
 
Another thing for me to check: ensure that filler plugs are vented, sounds like not all of them are.
venthole.jpg
 
GeorgeC said:
Another thing for me to check: ensure that filler plugs are vented, sounds like not all of them are.
View attachment 85549
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A lot weren't. The air can get out of the reservoir without that hole, but there are two problems: it either has to escape around the cap threads, which are quite fine and get sealed up by 5606 as it dries and gums up, or around the shaft, which has no seal, and if the fluid is topped up high enough it's into the shaft guide in the cap and any pressure in the reservoir pushes oil out around the shaft and makes a mess. The system can't really build that much pressure without the vented plug.
 
It doesn't look like IRAN of the lock-o-seal and o-ring would be a big job, but shops sure seem reluctant to touch the masters.
 
GeorgeC said:
It doesn't look like IRAN of the lock-o-seal and o-ring would be a big job, but shops sure seem reluctant to touch the masters.
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That's because they've never had them apart and maybe don't even have a manual. They're not a big deal at all. Getting them out and back into the airplane is a bigger job than opening them up, cleaning them out and replacing worn stuff.
 
Left side was vented, right side was not.

Also, I figured out why my right pedal always felt a little notchy. I guess you could say it was out of round:
IMG_2111.JPG
Looks like the left wasn't far behind:
IMG_2112.JPG
Sigh.

Good thing I ordered period-correct pedals yesterday.
 
GeorgeC said:
Left side was vented, right side was not.

Also, I figured out why my right pedal always felt a little notchy. I guess you could say it was out of round:
Looks like the left wasn't far behind:
Sigh.
Good thing I ordered period-correct pedals yesterday.
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Old airplanes are fun.

The main pivot holes look pretty worn, too. McFarlane used to take in old pedals and bore those holes and bush them with bronze. Don't think they've done that for a few years now. They have a PMA for new pedals. With bronze bushings. https://www.mcfarlaneaviation.com/products/product/AP2000-01/
 
Shops seem busy, despite covid.

Replacing the pedals without removing the rudder bars was a pain in the neck.

It was easy to vent the plug with just a hand drill and a vise.

Parts are on order, having both master cylinders overhauled (and likely new flex lines) this weekend.
 
GeorgeC said:
Shops seem busy, despite covid.

Replacing the pedals without removing the rudder bars was a pain in the neck.

It was easy to vent the plug with just a hand drill and a vise.

Parts are on order, having both master cylinders overhauled (and likely new flex lines) this weekend.
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New main springs for the master cylinders? If the old ones are weak but not replaced, the problem will persist.
 
Dan Thomas said:
New main springs for the master cylinders? If the old ones are weak but not replaced, the problem will persist.
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Yes. They'll be opened up anyway, springs are cheap, and I am tired of playing roulette.
 
Dan Thomas said:
That's because they've never had them apart and maybe don't even have a manual. They're not a big deal at all. Getting them out and back into the airplane is a bigger job than opening them up, cleaning them out and replacing worn stuff.
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ABSOLUTELY. My A&P and I did the toe and hand brake masters on my Cherokee last year. Rebuilding them was ridiculously fast and easy. Getting them in and out if the plane was torture.
 
Update from mx: turns out they were Goodyear master cylinders. One of the piston return springs was broken. Two overhauled master cylinders on order...
 
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One of the piston shafts was also gouged and did not slide smoothly.IMG_2232.JPG
 
dtuuri said:
Oh man, I really hate to see anybody working around aircraft with a ring on... :(
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Concur...when going to work on the plane or the boat, I always apologize to my wife for leaving my ring home, but she gets it. Way rather come home with intact fingers and limbs and a beating heart to an intact ring.
 
The Goodyear master cylinders will join the shrine of airplane parts, Clevelands are installed now.
 
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