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I found a marin team issue on a local marketplace. The frame is in good shape it seems and I have many m900 parts from the time so I'd love to re-build completely.

The main issue so far is the integrated rear mech hanger which is bent backward. Photos here:

https://imgur.com/a/MUehY23

Normally it is a straight line from top to bottom of the hanger, so I need to push back forward because now it has like a hockey stick shape.

I'm reading everything and it's exact opposite regarding how to bend it back so I'm really confused about next step. Some say it's best to do it cold because heating it will require to heat too hot and it will damage the steel. Others say it needs to be heated and it will not damage the steel. On the other end I see lots of videos of Paul Brodie brazing on many steel bikes and Old Shovel welding disc mount with TIG on steel frame too, and it seems to be fine?

How would you go about this? What do I need to know to maximise chances of success? Those frames are becoming pretty rare so if it can be salvaged it would be fantastic.

enter image description here

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    Steel derailleurs can definitely be straightened laterally without heat, because I've done it. Bending it in-plane you've got less to push against and less to measure against, and it will take more force, but it should still be doable
    – Chris H
    Dec 30, 2023 at 17:16

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Assuming it is steel, I'd go to a framebuilder and get a price to re-forge that. Had the frame been designed with a replaceable hanger, it would be a simple fix, sadly.

Using cold leverage at home runs the risk of snapping it clean off or weakening the hanger.


Heat will help, but you require oxy-acetylene. A MAPP (MAP-pro) burner or a propane/LPG burner won't be able to get the metal hot enough quick enough.

You need to get the dropout to around 500 degrees C to bend it. This is "red hot" and at the same time you must limit the heat travelling into the frame tubes - they're much thinner and will not cope with the heat.

Plus you have one chance to get the soft hanger in the right place, while maintaining alignment and squareness to the dropout


Third option is to work with what you have - make a template and cut a piece of steel to weld onto the existing bent hanger, such that it puts a new hole at the right location. This would look pretty awful.

A generic claw hanger might work if you mill/file enough metal from the dropout such that it becomes a slot, like `80's bikes had. Got to watch out for reduction in thickness.


Fourth is unbrazing or cutting the whole dropout from the frame, and either buying or making a complete new one and welding or brazing that back in as a replacement.

Side advantage here is that you can design in a replaceable hanger to stop this happening again. Use a commonly available hanger and next time it'll be a $20 part.


Another option is to single-speed it, but there's not a lot of meat there to mount an axle.

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    Thanks criggie, I'd love to try at home though, at the moment the frame is useless. If I fail, it'll still be useless. There is more upside in this case. Just unsure of how to go about it.
    – tweedi
    Dec 30, 2023 at 22:28
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    @tweedi Hopefully you didn't spend a lot on the frame, so if the repair goes badly you're not out a lot of cash. Personally I'd see a guy I know with a oxy-acetylene welding rig and we'd heat it mounted in a vise so the hanger is upward, wrapping wet rags around the chainstay/seatstay and opposite side. I'd also prepare a rod that can sit inside the NDS dropout to help with alignment, and some kind of rectangular pipe to act as a handle to move the hot metal. Finally think about quenching and tempering too, have a plan ready before starting. The M10 thread will need chasing afterward.
    – Criggie
    Dec 31, 2023 at 1:05

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