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Bent derailleur hanger question

Old 09-18-15, 12:14 PM
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Bent derailleur hanger question

I am working on an aluminum frame with a bent derailleur hanger. It is all aluminum without the replaceable hanger insert.

I have used the Park DAG on steel frames and on aluminum frames that had derailleur hangers that were bent.

This is a mid-90's Trek 1400. Is it safe / advisable? Any special considerations or cautions?
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Old 09-18-15, 12:19 PM
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It can be done , but you need to do it slowly and not too many time . If you bent it back and fore a few times yes it will break off .
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Old 09-18-15, 12:53 PM
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My only success with bending aluminum has been with heat. Warm with oxy/acetylene until it bends and keep heat on until its in the right spot. Bending cold only seems to crack parts.

-SP
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Old 09-18-15, 02:02 PM
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Originally Posted by speedy25
My only success with bending aluminum has been with heat. Warm with oxy/acetylene until it bends and keep heat on until its in the right spot. Bending cold only seems to crack parts.

-SP
NOOOO! do not change the heat treatment of an AL frame. The Op's answer is to first accept that their frame might break if the hanger alignment is tried. If they can't accept that then learn to live with the bend. If they can't do that also/instead then they just learned the true cost of an AL frame which doesn't have a replaceable hanger and a different frame will make them happier in the long run.

But more to the point of the possible aligning. This is done, COLD, in most every LBS most every week. We tweak hangers all the time, COLD. We use proper DAGs or just allen wrenches and a backing lever (screwdriver, cone wrench...) depending. This isn't rocket science. It's simple blacksmithy but WITHOUT THE HEAT. Do we ever break a hanger, yes. But it interesting that the only one's I've ever broken are the AL replaceable ones. After 40+ years of wrenching, frame building and such I can't say I've broken a intergraded hanger. I have refused to straighten some for various reasons though, first being the customer's directions after discussions. Andy.
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Old 09-18-15, 04:28 PM
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Do NOT heat that frame!!!! The 1400's were bonded (read glued) frames with the aluminum tubes bonded to internal aluminum lugs. Heat will certainly destroy the bonds and ruin the frame.
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Old 09-18-15, 04:32 PM
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Originally Posted by HillRider
Do NOT heat that frame!!!! The 1400's were bonded (read glued) frames with the aluminum tubes bonded to internal aluminum lugs. Heat will certainly destroy the bonds and ruin the frame.
Exactly right!

The standard way to get epoxy to release is to use heat...
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Old 09-18-15, 05:24 PM
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FWIW, I recently straightened the bent hanger on a Trek 3500 found at curbside. Done gently and slowly (I used an adjustable wrench), this is not likely to cause failure of the aluminum, as Andrew says. Go a little at a time so you won't overdo it and have to re-bend. Careful eyeballing worked for me, but some people put a bolt through the hole, fastened with a nut, and use that as an indicator of trueness; the bolt should be parallel to the axle.

Afterward, make sure the derailleur hangs vertically and parallel to the plane of the wheel. Mine needed straightening, which must be done without further damage to the hanger you just fixed! Take the DER off the bike to do this.
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Old 09-18-15, 05:37 PM
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I have used my hanger tool on my and a friend's Trek 5200 with no problems.
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