Bad timing...

In rec.aviation.owning Jay Honeck wrote:
Anyone know if it's possible for a brake to hang up and not release,
resulting in advanced wear like this?

Sure. Short answer: Check the flex line (rubber line) on that side.
If OK or not so equipped, see below.

Long answer:

When I got the engine running (for some value of running) in the first
car I've owned that's older than me, I of course had to take it around
the block. I had reasoned that its manual four-wheel drum brakes would
not respond as well as the power-assisted front disc, rear drum brakes
did on nearly every other car I had owned or driven. Still, when I got
to the stop sign just down the block, I was glad it was one of the
optional ones with the white stripe around it, because I got halfway
into the intersection before I stopped. When I let off the pedal and
tried to accelerate again, the car hesitated for a second, then there
was a ping! from one of the front wheels and the hesitation was gone.

At first I wondered if I was simply treading too lightly on the brakes,
so I got the car back up to 15 mph and literally stood on the pedal.
This still produced a rather anemic stop, so I was convinced something
was wrong. Again, as I tried to accelerate away, I was held back until
I heard the ping! from the front wheel. I carefully returned home to
investigate.

Online consultation with a group of enthusiasts brought a nearly
unanimous answer: The rubber lines in the brake system tend to
deteriorate on the inside as well as on the outside. Besides causing a
reduced flow of brake fluid and poor braking in general, a flap of
rubber will often form inside the line. This flap acts as a check valve:
when you stomp on the pedal and bring up the pressure in the system, the
fluid is forced past the flap and out to the wheel cylinder or caliper,
applying the brake. When you let off the pedal, the shoes or pads are
pushing back on the piston to return the fluid to the master cylinder,
but this pressure is not as great, and the flap is enough to prevent it
from returning. The result is that the brakes on that wheel stay
engaged. Eventually enough fluid may get back through to release the
brakes on that wheel - probably the ping! that I heard. Many people
said they liked to replace the flex hoses immediately on any old car new
to them, and then on a schedule of every 5 to 10 years thereafter.

After a little further inspection, I decided that although the master
cylinder and wheel cylinders were not original to the car, the flex
lines probably were. I ordered a new set, and when they arrived, I
swapped them out. I did a test on the old lines: with them lying on the
ground, not connected to anything, I hooked up my hand vacuum pump to
them. It should have been like sucking on a brand new soda straw, but
instead it was like sucking on a bottle - I could pull a 25" Hg vacuum
from either end of all the hoses. The brakes were probably only working
as much as they did because the hydraulic pressure in the system was
considerably higher, and could force a little fluid through the old
hoses. A road test with the new hoses proved much more satisfying; I
could reliably stop at both the optional and the mandatory stop signs.

One diagnostic for this problem in a car is to raise the wheels off the
ground and make sure they turn freely by hand. Then stomp on the brakes,
and make sure that the wheels don't turn. Finally, let off the brakes,
and see if the wheels turn freely again. If one of them doesn't, open
the bleeder valve on that wheel cylinder or caliper. If you get a spurt
of fluid from the valve and the wheel suddenly turns freely, then the
problem is probably in the lines or master cylinder. If the wheel is
still stuck, then the problem is probably in the wheel cylinder or
caliper.

An alternative way to see if a brake is dragging lightly is to travel in
a straight line for some distance, stop, then compare the temperatures
of the wheels from side to side. If you're optimizing for cheap, you
can check with a careful hand or wet fingertip. If you're optimizing
for shiny, this is a perfect excuse to buy one of those infrared remote
thermometers. If you can't travel in a straight line, one of the brakes
might be dragging more than lightly, or possibly the vehicle control
system is affected by ethanol.

I know that an airplane, in general, is not a car. On a Cessna 182, the
one airplane that I've been around the most, if you start at the wheels
and work in, the system is similar to a car. There is a pad moved by a
piston at the wheel. Then, there is some combination of hard line and
flex line that goes from the wheel back to the fuselage - the flex line
is there to account for relative motion between the wheel/landing gear
and the fuselage. Then it's hard line back to the master cylinder. The
mechanical linkage to operate the master cylinder is different, but the
principle is the same as in a car.

It could be that your airplane doesn't have any flex lines in its
braking system. In that case, you have to decide whether to go after
the wheel cylinder or the master cylinder next. You might be able to
swap existing parts from side to side to see if the trouble follows the
part or not. Or, tear down the parts from both sides, and play "One Of
These Things Is Not Like The Others."

Disclaimer: This is based on experience with braking systems on ground
vehicles. I don't have an A&P; I don't even have a TG&Y. Some of this
may not be allowable owner maintenance. Your mileage may vary.

Matt Roberds