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Straightening a RD cage

Old 07-18-22, 10:15 AM
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Lbxpdx
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Straightening a RD cage

I noticed the cage on my old Sachs Huret DuoPar eco is a bit bent. From what I’ve read, this was a common complaint back in the 80’s when this derailleur came out. Should I bend it back while on the bike or take the derailleur off and apart, then bend it against something flat?

also, is heat needed? I believe it is steel.

it shifts fine, but gets stuck when back pedaling.


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Old 07-18-22, 10:18 AM
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Personally, I'd try to do it on the bike--you'll get more leverage that way. I wouldn't heat it.

Be advised--sometimes cages can take weird compound curves--they might be fairly difficult to straighten perfectly.

Last edited by smd4; 07-18-22 at 10:35 AM.
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Old 07-18-22, 10:43 AM
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Originally Posted by smd4
Personally, I'd try to do it on the bike--you'll get more leverage that way. I wouldn't heat it.

Be advised--sometimes cages can take weird compound curves--they might be fairly difficult to straighten perfectly.
thanks. I don’t need it perfect, I just want to be able to back pedal.
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Old 07-18-22, 11:34 AM
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If you do it on the bike, I would be concerned about bending the integrated hanger and not the RD cage.

John

Edit added: As far as bending it off a bike. Get an inexpensive universal/claw type hanger and mount it in a vise.
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Old 07-18-22, 12:35 PM
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Bending it against something flat will not help, you have to overbend the metal to get it to deform and take a new shape.
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Old 07-18-22, 12:47 PM
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Originally Posted by 70sSanO
If you do it on the bike, I would be concerned about bending the integrated hanger and not the RD cage.

John

Edit added: As far as bending it off a bike. Get an inexpensive universal/claw type hanger and mount it in a vise.
You think the thick hanger will bend before the thin cage?
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Old 07-18-22, 01:04 PM
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I’ve straighten the hanger and a steel frame with a large crescent wrench and a square. It doesn’t take a lot of effort.

Whether or not straightening the RD will tweak it I can’t say. If it were me I’d take it off the bike. It might even be necessary to remove the outer plate.

It looks substantially out of line. I will say that the cage will break before the hanger.

John
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Old 07-18-22, 01:13 PM
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Originally Posted by 70sSanO
I’ve straighten the hanger and a steel frame with a large crescent wrench and a square. It doesn’t take a lot of effort.

Whether or not straightening the RD will tweak it I can’t say. If it were me I’d take it off the bike. It might even be necessary to remove the outer plate.

It looks substantially out of line. I will say that the cage will break before the hanger.

John
I figured taking the RD off and apart might be the best route, though I wanted the input of others with more experience.
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Old 07-18-22, 01:15 PM
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Well, a vice is a good idea too. It'll take some time before the cage breaks, if it's steel.

But anyway, if it can't be straightened, replacements are on eBay. Although I'd be inclined, myself, to upgrade to something more modern (i.e., a slant parallelogram).
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Old 07-18-22, 01:24 PM
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Originally Posted by Lbxpdx
I figured taking the RD off and apart might be the best route, though I wanted the input of others with more experience.
Taking it apart and getting the plates flat in isolation is what I'd do.
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Old 07-18-22, 01:27 PM
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Originally Posted by smd4
You think the thick hanger will bend before the thin cage?
probably not, but why mess with it?
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Old 07-18-22, 03:16 PM
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The hanger probably won't bend but there is a lot of flexion in the RD body that will occur when you
start to bend the cage if mounted on the bike. Best to remove from bike and dismantle the cage so only the inner cage
is exposed, then you can clamp in a vise and precisely bend it back. No heat needed.
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Old 07-18-22, 08:03 PM
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...that's one of the few rear derailleurs I routinely replace with something that works better.
I know thee are people who like them, but I never could get them to work as well as the long cage alternatives.

The ones I've encountered seem to wear out at all the various pivot points...I don't imagine bending and straightening will help that.
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Old 07-19-22, 05:53 AM
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Originally Posted by Lbxpdx
thanks. I don’t need it perfect, I just want to be able to back pedal.
Why "back pedal?" That's the most common cause of Duopar derailluer failure. If back pedalling is truly necessary for some reason, consider a different derailleur.
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Old 07-19-22, 06:49 AM
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Originally Posted by JohnDThompson
Why "back pedal?" That's the most common cause of Duopar derailluer failure. If back pedalling is truly necessary for some reason, consider a different derailleur.
since the bike has toe cages, sometimes I need to back pedal a touch to get my feet in.
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Old 07-19-22, 06:59 AM
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How valuable is the bike vs your time? I bend a lot of old RDs back into shape on bikes donated to non-profits. But I don't care about the bikes. If this is your baby, treat is as such and enjoy the process. Get out the old toothbrush and shine it as you go.
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Old 07-19-22, 07:51 AM
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Maybe because the bent cage throws the angle off a bit but it looks like the guide pulley is not aligned either.
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Old 07-19-22, 07:57 AM
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I would chunk it, I bet your bike has a lot of clattering.

If you want to give it a shot, align the dropouts, align the hanger, reinstall rd examine the top pulley align that to the cogs, then attack the cage align to the cogs. In fixing bends I try to reverse engineer the bends.
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Old 07-19-22, 08:48 AM
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Originally Posted by Mr. 66
I would chunk it, I bet your bike has a lot of clattering.

If you want to give it a shot, align the dropouts, align the hanger, reinstall rd examine the top pulley align that to the cogs, then attack the cage align to the cogs. In fixing bends I try to reverse engineer the bends.
cool. It shifts fine and is actually quiet. I’m a bit stubborn, so I like to get get things to work before I just replace them.

Last edited by Lbxpdx; 07-19-22 at 09:43 AM.
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Old 07-23-22, 08:42 AM
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Where you able to make the time to try yet?
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Old 07-23-22, 08:58 AM
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Originally Posted by Mr. 66
Where you able to make the time to try yet?
Yes. I was able to bend it back by hand while on the bike. It was rather simple. Shifts great and I can now roll the bike backwards or back pedal enough to get my shoes in the toe cages.
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