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Old 11-28-06, 12:00 PM   #1
DScott
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Bent derailleur hanger

Hi all,

The replaceable derailleur hanger on my Trek 1200 has bent, causing the Shimano 105 large cage rear der. to tilt in towards the hub. It causes increased noise while pedaling, but hasn't been bad enough to cause skipping or difficulty shifting, as far as I can tell. It's definitely riding off-center on the lower pulleys when it does this, which can't be a good thing. Front crank is a triple (30-42-52), and rear is a SRAM 9 spd. 12-26 cassette (which I'm told is getting worn). The chain measures out as stretched and needs replacement.

The LBS mechanic straightened it once using the DAG-1 and it seemed to be better for just a little while, but it is once again listing to port. There's about 2500 miles on this bike, and I'm a little surprised this has happened. I haven't dropped it or banged in to anything on the right side, AFAIK. I'm pretty good about keeping the chain clean and lubed.

I suspect that the chain line is the issue, since it became apparent after I had started to run more in the big ring. While I spend most of my time in the middle of the cassette (15, 17, 19 cogs), I think this puts the rear der. under a fair bit of tension. I'm afraid that is what bent the hanger.

My questions are these:

1. Can this kind of chain line tension bend the hanger? Hnagers are soft, maybe it's just worn out?

2. If/when I replace the der. hanger, what's to stop this from happening again?

3. Would a new chain/cassette help?

4. My goal is a compact crank setup (with the next bike), but I'm now even more worried about chain line problems. Does this kind of problem happen with compact (or any double) cranks?


Thanks for any and all help!
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Old 11-28-06, 12:20 PM   #2
Sheldon Brown
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Quote:
Originally Posted by DScott
The replaceable derailleur hanger on my Trek 1200 has bent...

The LBS mechanic straightened it once using the DAG-1 and it seemed to be better for just a little while, but it is once again listing to port. There's about 2500 miles on this bike, and I'm a little surprised this has happened. I haven't dropped it or banged in to anything on the right side, AFAIK.
It's surprisingly easy to bend one of these without realizing it.

Quote:
Originally Posted by DScott
I'm pretty good about keeping the chain clean and lubed.
This has nothing to do with it.

Quote:
Originally Posted by DScott
I suspect that the chain line is the issue,
No, chainline has nothing to do with bending derailer hangers under any circumstance.

Quote:
Originally Posted by DScott
... I spend most of my time in the middle of the cassette (15, 17, 19 cogs), I think this puts the rear der. under a fair bit of tension. I'm afraid that is what bent the hanger.
Definitely not. Chain tension is highest in the larger sprockets, but normal derailer chain tension never has anyting to do with bending hangers.

Quote:
Originally Posted by DScott
My questions are these:

1. Can this kind of chain line tension bend the hanger? Hnagers are soft, maybe it's just worn out?
Definitely not.

Quote:
Originally Posted by DScott
2. If/when I replace the der. hanger, what's to stop this from happening again?
You need to be very careful not to bash the derailer hanger. Are you sure it's actually bent? Maybe its the derailer that's bent...

Quote:
Originally Posted by DScott
3. Would a new chain/cassette help?
Definitely not related to the bent hanger, but it might help in other ways if the old one is worn out.

Quote:
Originally Posted by DScott
4. My goal is a compact crank setup (with the next bike), but I'm now even more worried about chain line problems. Does this kind of problem happen with compact (or any double) cranks?
Compact cranks are no more subject to chainline probems than anything else, and generally less than triples.

Sheldon "Barking Up The Wrong Tree" Brown
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Old 11-28-06, 12:52 PM   #3
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Thanks, Sheldon. The rer. der. seems OK to me, there's no signficant play in any of the pins and it *looks* straight independent of the hanger. Can the pivots seem solid and the cage still be bent or something?

It was an interesting experience. I've was told by two different LBS mechanics that the rear der. was OK, but I'm not quite sure what to believe now.

The first said the der. was fine, the hanger was fine, and offered no options. The second LBS mechanic took a look at it, ran the bike through all the gears, and then whipped out the DAG-1. He straightened the hanger., and pointed out that the long cage der. looked OK. He said that it was really flexed in the big chainring/larger rear sprocket positions, and suggested this might be pulling the rear der. over, and torqueing the hanger.

I might have misunderstood him, it was pretty quick.

However, it made sense to me that there might be enough force to re-bend an already weaked hanger. Maybe I previously bent it some other way, like if the bike fell over or got struck by something while in the garage.

How hard does the hanger have to be whacked to get bent?

The worn chain was an incidental finding. Glad to know it's not involved.

Either way, I'm going to have the LBS replace the hanger when I do their "tune-up", and see how that goes. I'm fairly confident in their work at this point, and like the attitude I got. This is a pretty reputable shop and the mechanic took the time to straighten it right then (for free!), just so I could ride that next day.

No hard sell, good service, and my BS meter wasn't pegged. A pleasant surprise these days.
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Old 11-28-06, 04:45 PM   #4
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Nine & 10 speed drivetrains have a high fiddle factor and the derailleur hanger's alignment needs to be mostly spot on to ensure smooth shifting. Although there's lots of other potential culprits - length & routing of cables/housing, cleanliness and condition of cables/housing/endcaps, cable tension, tightness of cassette lockring, condition of cassette/chainring teeth & chain, mechanical wear of shifters themselves (Keep in mind you change gears much more often with handlebar mounted shifters and the close spacing of 9 & 10 speed cogs, so the shifters, especially the right/rear one, wear quickly).

It doesn't take much of a bump to slightly tweak the hanger. Also, when the LBS tech is aligning the hanger, ensure he's checking it vertically and horizontally (For bending & twisting).
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Old 11-29-06, 08:34 AM   #5
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Thanks, I'll try and be there when he installs the thing.

My problem is wanting to buy the parts and the tools and doing it my self, but not sure I'm getting it *quite right* and never really knowing if it could work better.

Yeah, like I really need a *good* reason to buy more tools! This place should have a sign that says, "Welcome to BikeForums.net! Sorry about your wallet!"

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