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I have broken two SRAM X.0 rear derailleurs where the plastic cable guide attaches to the aluminum parallelogram body. A third was broken in shipping. The bummer about this is that the black plastic guide is the derailleur's prime mover. Acting like a large lever, it swings the derailleur across the cassette cogs as the cable is taken in with each successive shift. Once cracked, the guide cannot do its job because, without being attached at both of its fixing points, it cannot derive sufficient stiffness to move the parallelogram.
Scroll down to read SRAM's report
 SRAM's X.0 rear derailleur up close. The black plastic guide extending behind the derailleur body is attached to the lower parallel link. When the cable is pulled, the guide levers the derailleur downwards and inwards. R. Cunningham photo
The last one I broke bent the derailleur's riveted aluminum backing plate and cracked the location at the pivot shaft. I bent the plate into position with a tire lever and zip-tied the guide to keep it on the pivot shaft--a MacGyver fix that turned my Santa Cruz Blur LT-C into a three-speed, but got me down the mountain.
The guide is attached by a single rivet, and at the derailleur parallelogram shaft--where the plastic cracked and failed. The Zip-tie held the guide in place quite well, but it also held the derailleur in the largest cogs. R. Cunningham photo
As the SRAM X.0 rear derailleur is my favorite, this potential problem has become a concern. Up until recently, I have never given the survivability of X.0 components a second thought, but now, I wonder about my derailleur each time I have a small spill or bash through the rocks. Of course, there is a remote chance that my three failures are the only malfunctions of SRAM's plastic guide--but that's unlikely, considering that the part is large, slightly built and exposed to the elements.
SRAM WEIGHS IN ON THE PROBLEM
I talked with SRAM's Eric Schutt about the issue this morning. Schutt is an absolute straight shooter, so I can take his word without running it through my new Fluffy-Marketing-Guy-Doing-Damage-Control-Filter (Radio Shack, $49.99, PC compatible only).
Schutt says that he called SRAM's warranty folks, the BlackBox program manager, and the bike rental guys in Whistler where they have a fleet of oft' crashed bikes with similar X.9 derailleurs, and nobody has even heard of a cable guide failure like mine. Eric (and I'll heartily agree) says that the X.0 rear derailleur has been extremely reliable and in service for nine years without an issue. It surprised him that I'd have such problems this far down the road. Still, three failures in as many months is a red flag to me--so I figured it warranted a post.
As embarrassing as this may seem, I'll have to chalk up my three derailleurs to fate and eat crow. In the remote chance that anyone has had a similar failure or wants to discuss this further you can log onto Ask RC on the home page and I'll pick it up from there. Thanks Eric.
--RC
The rivet that fixes the guide to the lower parallelogram is partly hidden behind the buckle of the Zip-tie.
R Cunningham photo
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