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Bent Derailleur Hanger

3.5K views 8 replies 5 participants last post by  wim  
#1 ·
The front braze on derailleur hanger on my road bike seems to be bent. Is it possible to replace this or must I try to bend it back? The rear of the FD cage sticks out and will hit my crank when in the big run unless the front of the cage rubs the chain. Here are some pics of it from above so you can see how it's turning out. View attachment 285291 View attachment 285292
 
#2 ·
You know the derailleur can be adjusted rotationally on that braze-on mount (not a hanger, that's the rear derailleur) right? It very well could be bent, but it's also possible and more likely that the derailleur slipped on the mount. It looks like you need to check the high limit screw as well...and i think the cage of that derailleur might be slightly bent.
 
#3 · (Edited)
No, I don't. How do I do that? I've adjusted the high limit screw a lot and it shifts well but, the rear of the cage hits my crank arm...

Do I just loosen the bolt that holds the FD onto the mount and then rotate it? If I do that then it just twists back when I tighten it.
 
#4 ·
That's the idea, but if you really can't hold the derailleur in the proper position it might really be bent. Did anything hit it? I'd swear that cage looks slightly bent. Loosen the bolt and move the cage so it's roughly parallel w/ the chainrings, then tighten the bolt back up. If it wants to settle 'tail out' then adjust it a little 'tail in' so when you tighten it down it stays parallel. Make sure you undo the cable so it doesn't pull the derailleur down on the mount. Then start all over w/ your limit screws.
1) position derailleur correctly
2) shift rear to large cog
3) adjust low limit in front to @ 1.0mm
4) shift rear to small cog
5) attach front cable
6) pedal crank and slowly pull on the cable (by hand, under down tube) til the chain shifts onto the large ring
7) adjust high limit to @ 1.0mm
8) adjust cable tension if needed
test repeatedly to make sure everything is good...crank arm doesn't hit cage, chain doesn't drop or throw...
 
#5 ·
Those things can fatigue and get flexy. Give it a little wiggle and see if it seems to have a lot of flex.

I just went though this. I'd set things up so I was fine in the big ring and then shift to the small and there would be rubbing there. So I'd re adjust the small then shift to the big ring and rubbing there. The problem was the flex in the hanger and it flexed when I shifted esentially creating a moving target for me to adjust to. Basically I would have it set up perfectly, then shifting would flex the thing and make it no longer perfect. Drove me crazy because I never thought hanger flex was a potential cause. And it most definitely was.....I could bend it easy with just my fingers when I took it off.

New solid hanger.....problems gone.

Yours looks a little more substantial than mine and I had 25kish miles with a lot of front shifting......so it's less likely to be your problem but it's worth checking for.

Although, it doesn't sound like you've even tried adjusting yet. Maybe get things set up right first before you worry about what I said.
 
#6 ·
I've adjusted how both of you told me to and it didn't work. When I tighten the bolt that holds the FD to the mount, the FD turns out. That's what makes me think the mount is bent. I have the bolt tightened less than I would like but it doesn't seem to be slipping down. Its not sticking out as much and isn't hitting the crank. I'll give it a ride in a day or two and see how it does.
 
#9 · (Edited)
When I tighten the bolt that holds the FD to the mount, the FD turns out.
I've had something similar happen once and it was due to an incorrectly installed (at the factory) front derailleur mounting tab. As a field expedient, I made a beveled washer.

If I remember this right, I used one of those long, tab-like, slotted-hole washers that come with Look cleats. After grinding a bevel on it, putting a bend into it and inserting it between the tab and the derailleur, I was able to position the derailleur correctly. Not an elegant solution, but it worked and as far as I know, still works.

My problem was a vertical misalignment, but I don't see why an unequal-thickness washer or properly placed shim strip wouldn't work in your case as well.