Tost brake bolt shears off

I am wondering if others have experienced the shearing of a Tost brake
bolt resulting in brake failure - I'm speaking about the bolt which
extends from the hub and is secured to the aircraft frame (not
the bolt which extends for the wire lever attachment). I experienced
such a failure on my latest landing with a month-old Tost unit - I was
puliing more strongly than usual on the brake but not nearly as hard
as I could, and certainly not as hard as I would if it had been an
emergency situation. I was amazed that such could produce a bolt
shear - I would have thought that some other brake part would fail
before such a
relatively thick bolt would, but I am no mechanic. It makes me wonder
about the quality of the parts Tost is using. Is this a known/common
point of failure?

Jack Glendening

On Sep 1, 6:40 am, Jack Glendening wrote:
I am wondering if others have experienced the shearing of a Tost brake
bolt resulting in brake failure - I'm speaking about the bolt which
extends from the hub and is secured to the aircraft frame (not
the bolt which extends for the wire lever attachment). I experienced
such a failure on my latest landing with a month-old Tost unit - I was
puliing more strongly than usual on the brake but not nearly as hard
as I could, and certainly not as hard as I would if it had been an
emergency situation. I was amazed that such could produce a bolt
shear - I would have thought that some other brake part would fail
before such a
relatively thick bolt would, but I am no mechanic. It makes me wonder
about the quality of the parts Tost is using. Is this a known/common
point of failure?

Jack Glendening


I had not heard of that before. Is it possible someone substituted a
hardware quality bolt? Is it a disk brake or mechanical? The Tost disk
brakes used by DG are re-branded Cleveland parts available from
Aircraft spruce. Tost just changes the internal O-ring to make it
compatible with brake fluid. The Cleveland O-ring is for use with
hydraulic oil.

The head of the bolt I am talking holds the brake pad plates inside
the
brake hub with its thread end extending outside the hub for
attachment
to the aircraft frame. So it is an integral part of the brake
assembly as
it comes from Tost and I can't imagine anyone substituting for it. It
is
_not_ a single bolt simply used for attachment. Jack

On Sep 1, 8:50 am, Jack Glendening wrote:
The head of the bolt I am talking holds the brake pad plates inside
the
brake hub with its thread end extending outside the hub for
attachment
to the aircraft frame. So it is an integral part of the brake
assembly as
it comes from Tost and I can't imagine anyone substituting for it. It
is
_not_ a single bolt simply used for attachment. Jack

The same thing happen to a DG 400 in HI 2 mo ago

Tom

what kind of glider was this on? This would seem very unusual as literally
thousands of these wheels are in use on almost all glider types.
it would help to know this
tim

Please visit the Wings & Wheels website at www.wingsandwheels.com

"Jack Glendening" wrote in message
ups.com...
I am wondering if others have experienced the shearing of a Tost brake
bolt resulting in brake failure - I'm speaking about the bolt which
extends from the hub and is secured to the aircraft frame (not
the bolt which extends for the wire lever attachment). I experienced
such a failure on my latest landing with a month-old Tost unit - I was
puliing more strongly than usual on the brake but not nearly as hard
as I could, and certainly not as hard as I would if it had been an
emergency situation. I was amazed that such could produce a bolt
shear - I would have thought that some other brake part would fail
before such a
relatively thick bolt would, but I am no mechanic. It makes me wonder
about the quality of the parts Tost is using. Is this a known/common
point of failure?

Jack Glendening

Tim Mara wrote:
what kind of glider was this on?

This is a also a DG400. (the Tost assembly was purchased from W&W.) Jack

On Sep 1, 8:40 am, Jack Glendening wrote:
I am wondering if others have experienced the shearing of a Tost brake
bolt resulting in brake failure - I'm speaking about the bolt which
extends from the hub and is secured to the aircraft frame (not
the bolt which extends for the wire lever attachment). I experienced
such a failure on my latest landing with a month-old Tost unit - I was
puliing more strongly than usual on the brake but not nearly as hard
as I could, and certainly not as hard as I would if it had been an
emergency situation. I was amazed that such could produce a bolt
shear - I would have thought that some other brake part would fail
before such a
relatively thick bolt would, but I am no mechanic. It makes me wonder
about the quality of the parts Tost is using. Is this a known/common
point of failure?

Jack Glendening

Hi Jack - I believe you are talking about a 4.50 tire mechanical
(ie non-hydraulic) Tost brake? The wonder is not that the bolt
sheared, rather that your brake shoes (actually, the one shoe
doing any work) generated enough force to shear the thing.
I don't think this is a common point of failure (though another
post here recounts another incident). For these brake
assemblies modified to servo-actuate, the torque load
is carried through the cast aluminum hub from the cam
to this bolt, and the cast hub has been known to fail...

Make sure that the end of the bolt isn't sloppy where it
attaches to the gear fork, which maybe could provoke
a failure, replace the bolt, and never point the plane at
anything valuable whilst expecting this brake to stop it...

Hope this helps,
Best Regards, Dave "YO" ("Miss August")

Jack,
I believe you are describing the *anti-rotation* bolt
and I have seen them shear off when the hub was improperly
installed. This bolt must be mated with its receptical
on the side of the landing gear or the hub will spin
when brakes are applied, resulting in the hub spinning
almost 360 degrees before hitting the landing gear
with sufficient force to shear off the bolt.

This bolt must be mated before installing the axle
when re-installing the wheel. While we're talking about
wheels and tires, if after changing the tire, the axle
doesn't slide easily through the hub, you have probably
*pinched* the tube in between the hub halves.
JJ


At 00:48 03 September 2007, wrote:
On Sep 1, 8:40 am, Jack Glendening wrote:
I am wondering if others have experienced the shearing
of a Tost brake
bolt resulting in brake failure - I'm speaking about
the bolt which
extends from the hub and is secured to the aircraft
frame (not
the bolt which extends for the wire lever attachment).
I experienced
such a failure on my latest landing with a month-old
Tost unit - I was
puliing more strongly than usual on the brake but
not nearly as hard
as I could, and certainly not as hard as I would if
it had been an
emergency situation. I was amazed that such could
produce a bolt
shear - I would have thought that some other brake
part would fail
before such a
relatively thick bolt would, but I am no mechanic.
It makes me wonder
about the quality of the parts Tost is using. Is
this a known/common
point of failure?

Jack Glendening

Hi Jack - I believe you are talking about a 4.50 tire
mechanical
(ie non-hydraulic) Tost brake? The wonder is not that
the bolt
sheared, rather that your brake shoes (actually, the
one shoe
doing any work) generated enough force to shear the
thing.
I don't think this is a common point of failure (though
another
post here recounts another incident). For these brake
assemblies modified to servo-actuate, the torque load
is carried through the cast aluminum hub from the cam
to this bolt, and the cast hub has been known to fail...

Make sure that the end of the bolt isn't sloppy where
it
attaches to the gear fork, which maybe could provoke
a failure, replace the bolt, and never point the plane
at
anything valuable whilst expecting this brake to stop
it...

Hope this helps,
Best Regards, Dave 'YO' ('Miss August')

it would be most unusual that enough force could be supplied to shear the
anchor bolt unless it was not the proper anchor bolt ....
please send images of the wheel and bolt to myself and also to TOST

tim
Please visit the Wings & Wheels website at www.wingsandwheels.com



"Jack Glendening" wrote in message
...
Tim Mara wrote:
what kind of glider was this on?

This is a also a DG400. (the Tost assembly was purchased from W&W.)
Jack

Responding to several replies at once, yes this is the "anti-rotation"
nut on a mechanical Tost brake. Whether there should be any "wonder"
about the bolt failing depends a lot on how hard I was pulling on the
brake. While I braked harder than I normally do, it was with a
pressure I felt comfortable with and I was surprised that the brake
would break under those circumstances. I know I have on occasion
pulled harder on the brake in other gliders. And the failure did
_not_ occur at the time of maximum pull, so I guess some details of
this particular incident are in order.

The landing was on a old WW2 base with wide and long runways. I
misjudged my approach and landed faster than usual and beyond the
runway start markers where I normally touch down. I normally turn off
at the first turnoff (760 feet beyond the runway start) but did not
know if I could do that this time. So I pulled as hard as I felt
comfortable doing to see what would happen, intending that if I could
not get stopped by the first taxiway I would go to next one 300 ft
further down. But I did get slowed down enough to take the first
taxiway. I actually released pressure on the brake as I went into the
turn because I wanted to be sure of having enough speed to get to the
runway incursion markers on the taxiway (the turn is more than 90
degrees). After the turn was completed I could see I had more than
sufficient speed and tried to again pull on the brake but found no
response. So I think the bolt sheared during or just after the turn.
I found myself looking at the spinning prop of a facing airplane on
the same taxiway, just beyond a crossing (runway-paralleling) taxiway,
and thought "I'm going to have to do something drastic if this thing
does not stop before I get to that crossing taxiway!" Thankfully I had
correctly judged the speed needed prior to the turn and with full
spoilers I did stop about 20 feet beyond the runway incursion markers,
just before reaching the cross taxiway.

So possibly the additional side forces during the turn did something.
Another possibility is that heating of the brake by the heavy braking
prior to that point helped cause the bolt to fail. It has been
suggested by a private email that the bolt tempering may have been
faulty. FWIW the brake was newly installed by an aircraft mechanic
(not me) but one who has limited experience with gliders. I will plan
on taking some pictures the next time I visit the plane. All I know
at this point is that there is a nut on that bolt at the brake case
(as a spacer?) and the shearing occurred just outside that nut. I
assume that the missing bolt part was attached to the plate extending
from the fuselage for that purpose. I had had about 10 successful
landings since brake installation, but all with minimal braking.

My reason for bringing this failure to this forum was because I was so
surprised by the bolt breakage given the amount of force I applied, a
force I did not feel was undue based on my past experience with Tost
brakes, so was looking for comments by those who might have
knowledge/experience that I do not. I would be more understanding
about a bolt breaking if I felt I had pulled extremely hard. I really
believe that the force I applied was not unreasonable.

I would like to think my braking capability is limited only
by pad friction, not by the strength of some bolt or other part of the
brake! Certainly for my car that is the case - my car's braking is
not limited by part of my brake assembly failing. I certainly hope my
ailerons/rudders are that way - I don't want to think that if I yank
too hard on the stick my ailerons/rudder might break off ! If there
is some amount of pull beyond which a brake part will break, one will
never know just where that point is until a pull actually does go
beyond that point and the brake then breaks - so one never knows
exactly how much stopping power one has until after he's broken the
brake once.

Jack