robert schlatte

On an aluminum frame bike which had a misaligned derailleur I was gently attempting to bend the hanger back with the Park alignment tool when the replaceable hanger snapped. In examining the hanger which was made of an extremely hard and brittle material which I assume is aluminum although its brittleness is more like ceramic, it does not appear to be bent- it is very rigid. (In fact for purposes of my inspection, I glued it back together and it appears to be perfectly straight.) This led me to think that perhaps it is the actual frame dropout that is bent and not the hanger. I know the replaceable hanger is typically intended to bend first so as not to harm the frame. Is it possible that the hanger was okay but the dropout is bent? The bike is a Trek 7.6fx that a friend purchased on Craigslist so I don't know what caused the misalignment but there was a little gouge on the outside of the derailleur so I suspect an accident of a fall. My bikes are steel so I don't have much experience with replaceable derailleurs. Can any of you experienced mechanics provide some insight or direction. Thanks.

Delmarva

At this point it's going to be difficult to tell whether the original hanger was bent or not. Another hanger will allow you to determine whether the original oner was bent. Because the derailleur is dinged it may be bent.

robert schlatte

I will take a picture of the glued together hanger when I get home tonight and post it. Like I said it appears to be perfectly straight. In fact it so rigid, I have a hard time thinking it could ever bend as opposed to just breaking like it did. I have identified the hanger- #144- and will purchase a new one, but I am hesitant to do that if the actual bike frame has been compromised. Another question I guess would be if the aluminum frame is bent can it be repaired?

Homebrew01

Depends. If the dropout itself needs a little tweak to make it straight, then it can probably be done. But major re-bends are not usually a good idea.

dabac

I'm a bit wary about bending aluminium. But I've shimmed replaceable dropouts successfully enough to restore function a couple of times. Loosen the dropout from the frame, insert the shimming material of your choice in the appropriate places for the desired alignment correction and tighten the dropout again.

Delmarva

Steel can within limits be straightened but aluminum and white metal alloys don't take much re-bending. A picture of the glued together hanger won't tell much. Just try a new hanger and hope.

If that doesn't work then I would look at the derailleur because it is dinged.

FBinNY 

Replaceable hangers, which started out as a good idea, have become a good idea gone bad.

The very nature of the job calls for hangers made of ductile material that can handle some rough service. For a variety of reasons there will not be assurance that bolted on hangers will be perfectly square, so it's very common that they need some tweaking and bending (cold setting for the squeamish) to bring the RD into correct alignment. After all, this is why there's a tool to do so.

It isn't the material per se, as there are a number of grades and tempers of aluminum that are well suited, bit apparently some makers prefer a nice published sped like 6061-T6 to something that is actually right for the job.

Since yours is snapped, buy a new one, install it and tweak it home. If you're concerned about it snapping, pay a shop to do the whole job, and take the risk of failure off your hands

robert schlatte

Thanks for all the advice. In fact, I did just order a new hanger. Once installed if it isn't correctly aligned, I am not going to attempt to tweak it again. As suggested, I will leave that to a shop.

dsbrantjr

If your new hanger is still not square, perhaps filing the backside rather than bending the hanger would give a better outcome.

FBinNY 

Many (most?) hangers have steps and other issues that would make filing the back side difficult. Hangers are made (or are supposed to be made) to tolerate a moderate amount of bending.

What happens if you crash or the bike falls on the right side on a ride? Is the hanger supposed to resolute stay straight let the RD or frame take the impact? Is it supposed to snap like a piece of brittle plastic and have you walk home?

No, common sense tells us that a hanger needs to be made (and most are) to take some rough service in stride, allowing alignment after installation and some loads, and failing only at a point where not failing would mean damage to the frame. Think of hangers as fuses, and a 20amp circuit calls for a 20amp rated fuse, not a 10amp, or 30 amp.

robert schlatte

I replaced the hanger and that seem to have done the trick. The derailleur is now substantially aligned and shifts well.