spectastic

I don't know how it happened. It's not really affecting my shifting all that much, since it's a friction shifter. But I'm wondering if straightening it would make shifting better.

FBinNY 

It's hard to tell from the photo, but it does look as if the hanger is bent in a bit and the cage angled toward the rim a bit.

Making sure it's on straight can't help. One of the easiest tip offsto a bent hnger depends on your having set the limits correctly when you mounted the derailleur initially. The limits tend to stay put, so if later they were off, it would be a sign that the hanger moved. (almost 100% of the time inward). On my old road bike I could reset the hanger back to straight based on the RD limit screws.

cny-bikeman

If pulleys are not perfectly vertical - parallel to the freewheel - then yes - but it's usually the hanger to which the derailleur is attached that is bent. It may not greatly affect shifting except that it will not shift as crisply into the small cog or not at all, and more importantly if you shift to the large cog the derailleur may go into the spokes!

That style derailleur tends to bend easily when the bike falls, due to how far it projects out and the large distance from the axle to that projection. You can usually put a long allen wrench in the bolt that mounts the derailleur to the hanger and firmly but gently bend the hanger back out till the pulleys are aligned again. As FB points out if your derailleur shifted properly into the large and small cogs previously it should do so again if you get the hanger back to the right spot.

FBinNY 

To clarify, it isn't the RD that bends (usually) but the hanger. As cny-bikeman points out the beefy upper body of that RD tends to hit first when the bike falls over, and so pushes the hanger inward.

Otherwise it's fairly rare for a derailleur itself to bend, unless it's snagged in the spokes in which case the bend will be very obvious (think pretzel).

pierce

I used a straight edge on my screen, and although visually it looks a little bent, my straight edge thought it was pretty close to a straight line, but there's some wide angle barrel distortion in the picture, whihc makes it harder to judge precisely.

Can you take a similar picture from farther away, using a telephoto setting instead of wide angle ?

the bike doesn't even have to be upside down, it can be upright, just shoot from a relatively low angle, like axle height, but from 10 or 15' away.

cny-bikeman

Well, I did say it's usually the hanger to which the derailleur is attached that is bent but I see I did not edit the later part to say That style derailleur tends to bend the hanger easily... so thanks for the additional clarification.

pierce

that looks like an old school forged steel dropout, which has the hangar integrated onto it, and not via a separate insert.

compare the 'forged' dropouts here, https://sheldonbrown.com/gloss_dr-z.html#dropout

with the modern style like...
https://www.mandaric.com/bikes/bke_scc_da/re_der_hng.jpg

where the hanger is an insert bolted onto a recess on the frame dropout.

FBinNY 

I understood what you intended, but wasn't sure the OP who first asked about a bent derailleur would pick up on it, hence the clarification.

FBinNY 

These actually handle being horsed into alignment better than many bolt on aluminum hangers. However since they're not replaceable some common sense caution is indicated.

spectastic

anyone know how to correct this light bent without compromising the axle hook?

FBinNY 

The easiest way to do a home repair on this is to put a 6mm hex key into the upper mounting bolt and using that to gently bend the hanger. Eyeball the cage and bend enough that it's vertical.

Don't forget to reset the inner and outer limits when you're done.

xenologer

Ideally, you'd use a derailer alignment guage to fix this. One trick I've used when lacking one, is to take a spare rear wheel and thread its axle into the derailer hanger; then use it as a DAG.

zukahn1 

The best way is to use a DR hanger tool which is basically a long rod with bolt that scews into the hanger so you can easly bend the hanger into proper aliegnment. Nearly any good shop or bike coop should have one and getting the aliegnment right will often do wonders for shifting and how smooth a bike runs. After working some at a bike coop and using one I found bikes that people thought needed new DR's , chain and cassete/freewheel where fine after proper aliegnment.

fietsbob

Little pictures are inadequate to know , the thing has to be in front of Me.

its a pretty old drive train, so maybe not..

a lot of design changes have taken place since then.

might be time for a new bike to gain all the improvements.

cny-bikeman

As I said above, just use an allen wrench in the fixing bolt to gently bend back into place. Of course one can use an alignment guage/tool, but for a friction shifting derailleur it's not as critical. DAG's were just not available at most shops for many decades, and we managed just fine.

JTownCitycycle

even though the derailleur seems to lean a little right so does the horizontal plane of the hub so I would say it's extremely close if not straight IMO

Airburst

Another thing that confuses the issue is the fact that if the derailleur is worn, the pivots can develop slop, meaning that the cage can end up at an angle, giving the impression of something being bent even with a perfectly aligned hanger.

cyccommute 

I agree that it is usually the hanger that gets bent. But that style of rear derailer is very prone to bending of the cage itself. The lack of a second plate on the cage and that the cage materials is aluminum makes the cage much weaker. Putting that derailer into a parking rack, for example, could easily bend it.

Frankly, it doesn't look all that bad and, because it's friction, alignment isn't a hypercritical as it is for indexed shifting.

Kimmo

Before judging the hanger's straightness based on the angle of an old derailleur's cage, consider that aside from the not-so-likely chance the derailleur's bent, it's quite likely to be a bit worn and sloppy. A wiggle should suffice to indicate the latter.

The pics show an almost vertical cage; judging from those I'd say it's probably fine, particularly on a friction-shifted bike. A sloppy RD doesn't even matter that much.

Looigi

In my experience, RD alignment matters little if at all, as long as it's not way out of wack (9 and 10 sp indexed shifting). Adjust the limits and cable tension properly and it shifts as well as if it's perfectly straight.

ksisler

Although far from fashionable, one of those pie plate spoke protectors can be a rather cool aide to getting home at the end of a ride.

spectastic

come to think of it, I had sort of an accident with this bike a while back, where a lot of force was exerted down on the bike while it was standing diagonally. One of the seat stays was bent out of place; I managed to straighten it out pretty well. I bet the bent hanger is another result of that incident. The rear derailleur mechanics seems pretty solid to me.

Airburst

OK, bending stuff 101. When you bend a piece of metal, in this case a tube, it deforms by elongating permanently along the outside of the bend. In other words, part of it stretches permanently. When you straighten it, you can't compress that metal back to how it was before*, all you can do is stretch the rest of the tube until it's straight. One of your seatstays is therefore now slightly longer than the other, which may well be pushing the whole rear end out of alignment, which could be screwing around with your dropout alignment. I'd expect the force from the wheel being in the dropout to pull the whole rear fork end into alignment, but I wouldn't rule the bend out as a cause.

*OK, you can, but it would buckle out. This is also why you can't just kick a big dent out of a body panel on a car from the back of the panel and have it look the way it did before - the metal has stretched.

cny-bikeman

Although your observation is technically correct it would take a pretty significant bend to make the seatstay longer than the other by an amount that would affect alignment to any significant degree.

Airburst

It depends on how badly bent the seatstay actually was, but anyway, on second thoughts the additional length would tend to deflect the forkend downwards, not sideways. Not good for wheel alignment if it was severe, but not really an issue for the hanger.