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Old 07-18-11, 12:26 PM   #1
Blind
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`80's specialized hardrock - suntour xcm rear derailleur blew apart?

Picked up an old hardrock to flip, as I pulled the rear wheel off, moving the rear derailleur out of the way to get the wheel out, the swingarm deal popped out of place.

inside, there is a coil spring with a tab at each end.

inside the derailleur side, there's 2 pin holes, and the swingarm has a d-shaped grooved center lock and also has 2 holes for the spring tab to fit into.

After lots of fussing and cursing, I got it back together, but now the spring is very weak so it doesn't take the slack out of the chain, shifting still works fine but the chain goes slack now.

do I just need to take it apart and use a different tab hole for the spring, or does the spring need to be wound up?

Will take pictures if it would help, but I can't imagine I'm the only one who has done this.
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Old 07-18-11, 01:51 PM   #2
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I don't understand how the RD swingarm "popped out of place" originally. You mean you pivoted the RD clockwise to allow the rear hub axle to slide out, and the spring arm on the RD "popped" and lost tension? That would indicate that the spring tab has broken or the hole it was inserted into it has been damaged or loosed inside the RD. Sometimes, it's on the pivot arm. But it sounds like you removed it and tried to re-insert the coil spring. Of the 2 holes on the spring fixing plate, I typically choose the hole that requires the coil to be more tensioned (yes, shift over one). But it only makes a small amount of difference, and only when cross chaining in small cog rear, small ring front. Otherwise, under most use cases, I have sufficient chain wrap and tension on the RD. I would seriously look at the inside where the other end of the coil spring is inserted and see if that hasn't been damaged if indeed, the original swing arm "popped".
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Old 07-18-11, 05:15 PM   #3
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yeah, the swingarm has a locking mechanism that slots into a channel with a D shaped opening, apparently I lined up the arm perfectly when I was moving it out the way for it to fly apart on me.

everything on both sides looked as they should to me, the spring tabs weren't damaged, holes looked right to me, etc.

Would a worn chain cause the slack condition? The freehub and derailleur pullies spun fine for me by hand, the chain looks pretty good to me, not rusted or anything. But the bike has been sitting in storage for awhile, it was a cool $10 garage sale find.

If I can't get this sorted, what kind of rear derailleur could I use in place of this suntour xcm? I can't seem to find any on eBay for cheap right now, and not looking to put a ton of money into this bike, just looking to do a quick tune / clean up and flip. The shifters on the bike seem like an early indexed mtb style, but the clicker buttons move as you shift through the gears.
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Old 07-18-11, 05:38 PM   #4
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you need to wine up the spring by moving the cage ( the swingarm ) counter-clockwise one full turn .
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Old 07-18-11, 06:07 PM   #5
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Originally Posted by bikeman715 View Post
you need to wine up the spring by moving the cage ( the swingarm ) counter-clockwise one full turn .
ok, I'll give that a shot tonight, thanks!
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Old 07-18-11, 07:02 PM   #6
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I just overhauled an XCM recently. Black plastic swing arm facing the spokes, right? It wasn't quite a full turn. And there were two obstacles in the way when trying to wind the spring with the long arm. First, there is the derailleur hanger bolt that sticks in a little. Then there is a stop bolt sticking out from the front side of the arm (metal screwed into metal arm) and this can't wind past the stop ridge on the RD body. The technique I used was to keep the arm at an angle with spring tab still stuck in the hole and gently wind up the spring. Passing over the hanger bolt was easy since I can also push the RD body inward. But tension increases as you wind, and I was able to just angle the derailleur arm over the stop ridge, and then push flush against the face of the pivot bolt as tension increased. Then I could secure the arm to the body. But it wasn't quite a full turn. The initial of position of the arm was more like 1 or 2 o'clock with the spring unwound. You wind counter-clockwise past obstacles and tension gets pretty high. Good luck!
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Old 07-31-11, 12:30 PM   #7
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giving it a spin and remounting the chain was the trick, got it all sorted out yesterday, thanks all!
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