PatrickGSR94

I don't know what the heck happened. I bought an Alivio rear derailleur off a guy, and when I went about installing it onto my bike frame, the hanger just snapped right off at one of the screws, while in the work stand. Could it be just because this frame is fairly old? It's an aluminum KHS frame about 20 years old or so.

Luckily KHS still has this hanger available, but it just sucks because this was supposed to be a budget spare parts build that I would have had ready to ride by this weekend, with awesome weather. But now I have to wait another week or more, with $30 more that I hadn't planned on spending.

kevindsingleton 

Ouch! That does suck. Probably just fatigued from years of use.

Guess you'll have to ride your other bike, this weekend. Don't let this stop you enjoying the rare fantastic weather!

Wilfred Laurier

It had probably already been bent and manually straightened more than once. This works as a temporary fix, but replaceable derailleur hangers are replaceable precisely because they are not repairable.

andr0id

I would bet that area where it starts to get thin behind the bolt was corroded. When you put some pressure on it, it broke.
Does the broken edge look clean an shiny or chalky white and gray?

PatrickGSR94

Nope, no corrosion that I could tell when I removed it.

Most places I looked wanted $30 for a new RD hanger, plus shipping. Surprisingly, KHS was the cheapest at $20 plus shipping.

As far as riding, I had planned on riding around looking for off-road connections between neighborhoods. My other bikes aren't set up for off-road which is why I'm building this one back up as a type of "gravel grinder" bike. Oh well, I'll just have to stick to the road for now, I guess.

Homebrew01

Installing a rear derailleur does not stress the hanger, so it must have been 99% broken already.

Bill Kapaun

If it was getting ready to break, consider yourself lucky.
No worries about "eating" a RDER, wheel....

fietsbob

get several while they are still available .

leob1

Maybe your bike is telling you it wants to be a single speed!

Andrew R Stewart 

Given the obvious wear on the frame (scratches at stay ends) it's likely that a previous stress (or many stresses) started the fatigue process which resulted in a weaker hanger. That the hanger also has varying steps in it's thickness and other stress risers (mount screw holes) it's no surprise that it broke. Did you get a second hanger to be ready for the next time (and save on the shipping costs too)? Andy.

alcjphil

+1 That hanger broke at a very good time

PatrickGSR94

I've had the bike since 2006 and put about 1,000 miles on it in that time, and it's only been off road a couple of times. Mostly ridden on roads. Never crashed.

Not sure why it would be fatigued. Nothing has ever impacted the hanger that I know of. When I removed the original RD about 6 months ago to put on the Marin utility bike (signature), it was working and shifting fine then. It's been hanging up in the garage ever since.

Rambino

Think yourself lucky it didn't happen whilst you were cruising at 20 mph along a busy road during rush hour, which is exactly what happened to me a few months ago. Scary would be an understatement. Later that day I took the broken hanger to my LBS and they asked if I'd had a fall or dropped the bike recently, at which point it suddenly dawned on me, that very morning a gust of wind had blown my bike from leaning up against a wall down to the ground - derailleur side down. So, in essence, the hanger did its job: it protected the frame. It's there to be a sacrificial lamb for the greater good of protecting a much more expensive bike frame.