It's a cold and dreary day, and I'm on call w/the ambulance service, so it seemed like the perfect morning to have a go at installing the emergency hanger in the comfort of my basement. It works! I can vouch for that.
The practice run was well worth my time. Being broken down on the trail and being feasted upon my mosquitos is a lousy time to learn new skills. Simple tasks at home become surprisingly difficult when one is under pressure and being chewed up by bugs.
I began with a 2007 (I think) Rockhopper frame running a non-Shadow, XT derailleur and an eight-speed drivetrain:
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I pretended that my hanger was broken to the point where I was forced to remove it. I'm glad I did this, because it led to complications. However, if you do not remove the old hanger, then you may not have enough extra skewer to safely accommodate the width of the emergency hanger. In my case, the space I gained by removing the old hanger is what gave me the skewer-length to add in the emergency hanger.
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What I did not anticipate is that removing the old hanger resulted in the smallest cassette cog being too close to the chainstay. The small cog was unusable. The following photo shows the problem from one vantage point:
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And this next photo shows clearly how the removal of the original hanger allows the hub bolt to sit in the freed up space, thus moving the cassette too close to the chainstay. I could not physically rotate the pedals with the chain in place -- at least not without gouging and damaging the frame. I actually tried fairly hard. With the chain on that small cog, things were jammed up pretty good.
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To solve the problem, I gave up my high gear. The high-limit screw gave me just enough adjustment that I was able to configure the derailleur not to drop into the small cog.
The next photo illustrates another issue. Look at how the derailleur is rotated forward and jammed up against the chainstay:
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I was not able to prevent this forward rotation. IMHO, just live with it. We're installing an emergency hanger, after all.
Surprisingly, I did not need to adjust the low-limit screw. I also ran into the sort of shifting trouble that you would encounter from a bent hanger. So I threw on the hanger alignment gauge. This next photo shows how bad off the alignment was (thru no fault of the hanger):
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The hanger itself is perfectly flat. The problem is that Specialized did not design the
outside of the dropout to serve as an alignment surface. Clearly on this particular bike I was not going to get perfection in shifting.
I did get pretty good results though -- good enough that I would probably finish a ride. There were a couple of spots on the cassette where a click of the shifter would not cause a shift, and a couple of spots where I'd get a double-shift, but things worked well enough that I would probably finish a ride. At the very least, I'd be able to walk back home.
Hmmm....I guess another lesson-learned here is that the emergency hanger might not help if you just have a slight bend in your original hanger. If the original hanger is still usable, you probably are just as well off in sticking with it.
So it was an interesting experiment. I'm definitely better prepared now should I ever need to use the emergency hanger on the trail. It's going into my pack, for sure.
EDIT: I had to pull slack from the shifter cable after bolting the derailleur onto the emergency hanger and adjusting the high limit. It probably goes without saying that one should be comfortable in shifter- and derailleur-adjustment before attempting to install an emergency hanger.
One last Edit: I should have, but did not, take the bike outside and actually ride it. Sorry. Didn't think of doing that until after I had put the old hanger back on.