DANGER: Trek multitrack 7300 (hybrid) aluminum bracket sheers off, rips apart entire rear end of bike

Hi,

Because this is a hybrid I'm not sure whether to place it in racing or
off-road. But here goes my story.

Saturday afternoon I was riding along a clean flat nature trail; no
sticks in the gears, no nothing. I was going at an even speed of
about 20-25mph in the next-highest gear when all of a sudden I hear a
*SNAP*, then something smashed into the rear spokes, causing an almost
instant stop. I was lucky I wasn't going downhill when this occurred,
or I would've flown over the handlebars.

It turns out that a small piece of the aluminum frame supporting the
gear shifter wore out due to metal fatigue. The shifter mechanism
ripped off the aluminum frame, got caught in the rear spokes, and
destroyed the entire rear end of the bike. Several spokes are broken
and/or bent. The shifter mechanism is bent in several places, the
shifter wire is shredded, and the front crank apparatus also has some
damage due to the sudden awkward pull on the chain.

I was not happy. I had to walk 8 miles home while contending with a
pair of minor stress fractures in the legs (I was biking because I
can't run for the moment). I've contacted the dealer but so far no
reply. This $420 bike is just barely over 2 years old, with less than
500 miles on it. I expected to get more than a dollar per mile for
this bike, and I'm really not happy with Trek's poor design of this
frame and model.

If the dealer or Trek will support the repair of this obvious
manufacturer's defect, I will keep you apprised.

Dan

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What's a "shifter mechanism", is it different than "gear shifter"? I
guess the "shifter wire" is just the cable and the "front crank
apparatus" is just the crank.

So in other words the rear derailer hanger broke off, the derailer got
caught in the rear wheel, a few spokes broke and you've got a bent
chainwheel.

Dan:

You cite the cause as "metal fatigue," but that *may* be premature.
The problem you note is not that uncommon (derailer goes into the
spokes), though the circumstances under which you experienced *were*.
Uusually, the rider shifts to the lowest gear (closest to the wheel) in
back and the rear derailer, the stops of which have not been correctly
set, smashes into the spokes.

It's really, REALLY unlikely that the derailer hanger (I think that's
what you are describing) failed initially and caused the rest of the
event.

What is the year and model of the bike? I ask because I want to know
if it has a "rapid rise" rear derailer. In that case, it's just barely
possible that the "snap" you heard was a cable letting go. If that is
the case, given your reported speed, the RD would have been pulled back
suddenly to the closest-to-the-spokes position, and could have smacked
into the spokes. That could have broken the derailer hanger. But
that's all speculation, based on it being that kind of RD.

(I assume from your description that the accident stopped you
*immediately*--in essence, that the rear wheel started to skid, as if
you had a locked rear brakes.)

Beware of describing this to your LBS as an "obvious manufacturer's
defect" and talking about "Trek's poor design," etc. Those sort of
statements will almost immediately place you in their mind as a
"JRA"--the sort of person who brings in a thoroughly trashed bike and
complains that they were "Just Riding Along" when the wheels fell off,
the handlebar fell off, the frame split in half, etc. LBSes generally
don't deal well with this kind of situation--it sounds like you're
preparing for a lawsuit.

Instead, take the bike in and explain the symptoms, then ask them what
*they think* happened. If it's a half-decent shop, this can be a very
positive experience.

Dan wrote:
Hi,

Because this is a hybrid I'm not sure whether to place it in racing
or
off-road. But here goes my story.

Saturday afternoon I was riding along a clean flat nature trail; no
sticks in the gears, no nothing. I was going at an even speed of
about 20-25mph in the next-highest gear when all of a sudden I hear a
*SNAP*, then something smashed into the rear spokes, causing an
almost
instant stop. I was lucky I wasn't going downhill when this
occurred,
or I would've flown over the handlebars.

It turns out that a small piece of the aluminum frame supporting the
gear shifter wore out due to metal fatigue. The shifter mechanism
ripped off the aluminum frame, got caught in the rear spokes, and
destroyed the entire rear end of the bike. Several spokes are broken
and/or bent. The shifter mechanism is bent in several places, the
shifter wire is shredded, and the front crank apparatus also has some
damage due to the sudden awkward pull on the chain.

I was not happy. I had to walk 8 miles home while contending with a
pair of minor stress fractures in the legs (I was biking because I
can't run for the moment). I've contacted the dealer but so far no
reply. This $420 bike is just barely over 2 years old, with less
than
500 miles on it. I expected to get more than a dollar per mile for
this bike, and I'm really not happy with Trek's poor design of this
frame and model.

If the dealer or Trek will support the repair of this obvious
manufacturer's defect, I will keep you apprised.

Dan

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On 28 Mar 2005 04:41:43 -0800, "Andy M-S"
wrote:

Usually, the rider shifts to the lowest gear (closest to the wheel) in
back and the rear derailer, the stops of which have not been correctly
set, smashes into the spokes.

I had been in the same gear for about an eighth of a mile before it
occurred. It was a very normal, straight length of trail and was
cruising normally.

It's really, REALLY unlikely that the derailer hanger (I think that's
what you are describing) failed initially and caused the rest of the
event.

I will show a picture of the aluminum support torn off the frame.
It's fuzzy but the blue part is the piece of the frame that's ripped
off. Is it normal for the derailer support to rip off the frame?

http://home.ptd.net/~vstevans/web/bike.jpg

What is the year and model of the bike? I ask because I want to know
if it has a "rapid rise" rear derailer. In that case, it's just barely
possible that the "snap" you heard was a cable letting go. If that is
the case, given your reported speed, the RD would have been pulled back
suddenly to the closest-to-the-spokes position, and could have smacked
into the spokes. That could have broken the derailer hanger. But
that's all speculation, based on it being that kind of RD.

The cable is still in place on the derailer (albeit the sheathing and
hair of steel are protruding in places from going around the wheel).
Even so, I cannot believe that a cable stuck in the gears would rip
apart the aluminum frame of the bicycle.

I sounded like I was ready for a lawsuit because I figured this would
be like trying to talk to a car dealer..."we're out of warranty, so
tough luck". And I was seriously considering buying a road bike for
the summer

Dan

On 28 Mar 2005 04:41:43 -0800, "Andy M-S"
wrote:

What is the year and model of the bike? I ask because I want to know
if it has a "rapid rise" rear derailer.

It was purchased in late 2002 (November). It's a Trek multitrack 7300
hybrid (blue)

Dan

If it has a rapid rise derailleur, the initial snap you heard may be
that a corroded cable broke, or the screw that clamps the cable to the
derailleur may have let go. Either case would send the derailleur
toward the spokes. If the stop wasn't set properly, it might then
slam into the spokes and do all the things that happened.

It is possible for the bike to shift normally even though the stops on
the derailleur are not set properly. In the case of a rapid-rise
derailleur, the shifter lets cable out to shift toward the bigger cog.
If the cable were adjusted so that the shifter stops the derailleur
instead of the stop screw stopping the derailleur, a sudden release of
the cable could cause the derailleur to go beyond its normal range.

Of course, if it isn't a rapid rise derailleur, none of this is your
problem.

If the dealer or Trek will support the repair of this obvious
manufacturer's defect, I will keep you apprised.

It is not at all obvious that this is a manufacturer's defect.
Misadjustment combined with cable failure could easily cause this sort
of thing to happen.

Dan wrote:

Hi,

Because this is a hybrid I'm not sure whether to place it in racing or
off-road. But here goes my story.

Saturday afternoon I was riding along a clean flat nature trail; no
sticks in the gears, no nothing. I was going at an even speed of
about 20-25mph in the next-highest gear when all of a sudden I hear a
*SNAP*, then something smashed into the rear spokes, causing an almost
instant stop. I was lucky I wasn't going downhill when this occurred,
or I would've flown over the handlebars.

It turns out that a small piece of the aluminum frame supporting the
gear shifter wore out due to metal fatigue. The shifter mechanism
ripped off the aluminum frame, got caught in the rear spokes, and
destroyed the entire rear end of the bike. Several spokes are broken
and/or bent. The shifter mechanism is bent in several places, the
shifter wire is shredded, and the front crank apparatus also has some
damage due to the sudden awkward pull on the chain.

I was not happy. I had to walk 8 miles home while contending with a
pair of minor stress fractures in the legs (I was biking because I
can't run for the moment). I've contacted the dealer but so far no
reply. This $420 bike is just barely over 2 years old, with less than
500 miles on it. I expected to get more than a dollar per mile for
this bike, and I'm really not happy with Trek's poor design of this
frame and model.

If the dealer or Trek will support the repair of this obvious
manufacturer's defect, I will keep you apprised.

Dan



Dan,

Given that TREK uses CAD/CAM and extensive quality control to design its
bikes, the metal fatigue on the derailleur hanger was most likely due to
damage that occurred in shipping or when the 16 year old mechanic who
put the bike together at the shop you got it from took it for a spin and
mashed it against a curb or something (believe it or not teenagers who
make minimum wage do stupid stuff like that).

One of the most common things in a crash is for the derailluer hanger to
get bent. And the way most people "fix" it is to bend it back, not
realizing that doing so causes substantial yet invisible metal fatigue.

So calm down on the CONSUMER PRODUCT WARNING thing unless you know for a
fact that defect originated in the manufacturing process.

Thanks,

Magilla

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Excellent point. People who are used to steel frames will bend back
derailer hangers; you can't do that with aluminum once it's been
damaged. If the hanger had ever been bent back, that could weaken it
to the point where failure might be possible.

BTW, this is why the Trek aluminum frames generally include
*replaceable* derailler hangers...if you bend it, you can replace
it--usually two or three small screws fasten the hanger to the frame.
I couldn't see well enough from the photo to tell, but there's no
chance that one or more of these screws had fallen out, is there?

On Sun, 27 Mar 2005 21:16:11 CST, Dan may have
said:

Hi,

Because this is a hybrid I'm not sure whether to place it in racing or
off-road. But here goes my story.

Saturday afternoon I was riding along a clean flat nature trail; no
sticks in the gears, no nothing. I was going at an even speed of
about 20-25mph in the next-highest gear when all of a sudden I hear a
*SNAP*, then something smashed into the rear spokes, causing an almost
instant stop. I was lucky I wasn't going downhill when this occurred,
or I would've flown over the handlebars.

It turns out that a small piece of the aluminum frame supporting the
gear shifter wore out due to metal fatigue. The shifter mechanism
ripped off the aluminum frame, got caught in the rear spokes, and
destroyed the entire rear end of the bike.

I find a different analysis more plausible; the rear derailleur cage
is much more likely to have snagged in the spokes, following the wheel
around and ripping the der support from the dropout in the process.
The der support tab has so little strain on it that it will not fail
due to "metal fatigue" even after an extremely long period in service.
There are at least three other ways by which the cited failure could
occur in my experience.

Several spokes are broken
and/or bent.

Quite typical of a spokejam due to der cage snagging.

The shifter mechanism is bent in several places, the
shifter wire is shredded, and the front crank apparatus also has some
damage due to the sudden awkward pull on the chain.

This should tell you something. Had the der mounting tab merely
failed, the der would have dropped off and hung from the chain, but
would not have been likely to get into the spokes; the der has to be
firmly mounted and the der cage extended (which won't be the case if
the der's mount breaks) in order for the cage to be able to grab the
spokes.

I was not happy. I had to walk 8 miles home while contending with a
pair of minor stress fractures in the legs (I was biking because I
can't run for the moment). I've contacted the dealer but so far no
reply. This $420 bike is just barely over 2 years old, with less than
500 miles on it. I expected to get more than a dollar per mile for
this bike, and I'm really not happy with Trek's poor design of this
frame and model.

If the dealer or Trek will support the repair of this obvious
manufacturer's defect, I will keep you apprised.

I suspect that failure analysis will determine that either the der had
been bent prior to the incident, putting its cage swing path into the
conincal region of the drive-side spokes, or that the der was stiff
due to congealed lubricant producing a motion pattern that put the der
into the spokes. I have had both types of failure occur; neither
would be a warranty matter.

Keep us informed in any event; it will be instructive for all
concerned if there's an actual defect involved.

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