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Old September 29th 09, 04:29 PM posted to rec.bicycles.tech
Tim McNamara
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Posts: 6,945
Default Broken steel road bike fork

In article
,
wrote:

On Sep 29, 5:42*am, jim beam wrote:
On 09/28/2009 09:37 PM, wrote:

So, I've been noticing that the front brakes of my road bike were
acting "grabby" in that the front would shimmy pretty badly just
as I'm coming to a stop. *The rims felt a little sticky, maybe
some Gatorade got on them and it hasn't really rained in a while.
*I cleaned the wheels last night and rode into work today. *It
was still bad, but didn't seem as bad. This has been going on for
a week, I didn't think anything of it. *I decided to not ride
after work and just come home, coming down the driveway, the
grabby-ness was really pronounced, so I figure that the brake
pads must be contaminated with something. When I took the wheel
off, my heart skipped a beat. *Without much effort, this is the
result:


http://www.bitrealm.com/misc/fork/p1000783.jpg
http://www.bitrealm.com/misc/fork/p1000784.jpg
http://www.bitrealm.com/misc/fork/p1000785.jpg


It was hanging by no more than 2mm of steeel. *I shudder when I
think of the roads I was about to go on, including one really bad
bump at the bottom. *I don't think it would have held together
and when you lose the front like this, it's going to be bad.


The shimmy was the wheel moving back and forth due to the fork
leg being fatigued. *There hasn't been any accident damage since
I put this fork on the bike. *The crack was almost all the way
through, starting from the BACK of the fork leg.


The crack initiating in the back of the leg is not unusual.

chrome plate is bad for fatigue - it contains many fatigue
initiators.


Chrome plating *can* result in embrittlement but does not necessarily do
so. Millions of bikes and other load bearing appplications are chromed
without such failures happening.

The reason for the failure seem pretty self-evident in the photo. Note
how the crack followed the shore line of the socket so perfectly, and
note the relative thicknesses of the metal. Note also the lack on a
reinforcement tang on the inside of the fork leg.

for the future, consider quality cfrp - unless abused, it's pretty
much "fatigue proof".


More clueless advice from "jim beam."

This fork was on the bike for about 8 years and had probably around
12K miles on it in that time.

I would like to find a 1" threaded replacement that has eyelets for
fenders, but they seem pretty thin on the ground. I can find the
exact same fork shown here (in black) that I could still buy. It was
a 200 mm steerer tube with 35mm of threading. Cut, it is 190mm with
25mm of threading. The one shown here was made for 27" wheels and I
just run long reach calipers. I had to have the crown race cut from
27 to 26.4mm.

If not, any 1" threadless forks with eyelets and room for fenders?


Harder to find these days since most aftermarket forks are aluminum or
CF, lack eyelets and are for 700C wheels (if the bike was made for 27"
wheels, going to a 700C fork will affect the geometry). But I would
think that any bike shop with a QBP account could order you a fork to
fit. Or you could have one made, but that would be expensive.
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