Derailleur derailed.
May 7, 2012 6:34 AM   Subscribe

The "hanging bolt" or "pivot bolt" assembly which held the rear derailleur to the frame of my son's old mountain bike disassembled while he was riding it and vanished. Is it possible to find generic replacement parts or does it need a whole new derailleur (it's an old Suntour Accushift \alpha-2000)? What's the cheapest way to get this bike running at this point?
posted by to Sports, Hobbies, & Recreation (13 answers total)
You could call around to a couple shops, but really, just replace the derailleur. The old derailleur is probably worn in such a way that a new bolt would fit funny.
posted by notsnot at 6:48 AM on May 7, 2012

Same thing happened to me. A friendly local shop with a box of bits gave me a replacement bolt. Even the least-expensive replacement derailleur was out of my budget at the time.
posted by anadem at 6:56 AM on May 7, 2012

The derailer you describe is well over twenty years old. If you have a bike shop nearby that stocks old used parts, there's a slight possibility you could find a old SunTour derailer that would have a compatible bolt. If that's the case, expect to pay 4-20 USD depending on condition.

More likely, you will have to buy a new derailer and use the whole thing. You can get a new cheapo derailer for under 20 USD (like stamped steel cheap) but the issue here is indexed shifting. SunTour is long out of business at this point, and assuming your son's bike has a complete SunTour drivetrain throwing on some other brand of derailer could mess up the shifting. If your son can operate the gears in friction mode (no indexing) then just about any derailer will work provided it can handle the gear range of the freewheel in back.

I hope this isn't too technical; I know you just want the thing to work but parts incompatibility is one of the bike industry's bugbears. It might actually be better just to pitch this question to a shop, being clear with them how much the bike is worth to you.

The Sheldon Brown site is an almost universally loved bicycle information source and can help you find what parts are compatible.
posted by werkzeuger at 7:18 AM on May 7, 2012

Also I'm seeing an Alpha 2000 rear on ebay right now for 39 USD. (I think that's painfully high for an old derailer, but that's just me).
posted by werkzeuger at 7:37 AM on May 7, 2012

I'd take it to a competent bike shop. In our shop we have several bins of odd bolts and nuts, including the bolt you need, and we're happy to dig through it and find something that works.

If that fails, they should be able to supply you with a derailleur that will get you back on the road. $40 for that used derailleur on eBay is laughable.
posted by spikeleemajortomdickandharryconnickjrmints at 8:08 AM on May 7, 2012

It's just a basic bolt, nothing that's all that unique to derailleurs except in that it might have been chrome-plated. A good hardware store ought to be to able to provide a close-enough bolt for fifty cents or so.
posted by jon1270 at 8:33 AM on May 7, 2012

I have a bunch of old Suntour derailleurs, and I think they all have the same bolt diameter, but I seem to remember varying lengths. If you can find one that's long enough, you can shim it up to fit.

My accushift shifters, which I've never mounted, can be switched out of index mode to continuous shifting (which anyone who has these has probably done already, since the index system worked so poorly) so you may not have to worry about that.

I haven't used a modern derailleur on one of my own bikes, but I think the old Suntours work extremely well, and I'd be reluctant to give one of them up without a struggle.
posted by jamjam at 8:37 AM on May 7, 2012

Nix my answer; I was thinking of a different bolt, on a different sort of derailleur. That one is special enough that you should head to a bike shop, not a hardware store.
posted by jon1270 at 9:15 AM on May 7, 2012

Go to a bike shop. Derailleur hangers are special bike parts that a bike shop will have. This shouldn't be an expensive fix, and they will probably have good-quality used parts they can replace yours with--Suntour Accushift parts were decent but not especially high-end, they will be able to replace it with something similar for a relatively low cost.
posted by epanalepsis at 10:51 AM on May 7, 2012

Also, derailleurs come in different bolt sizes, and with different capacities (mountain vs road etc) so a knowledgeable mechanic will make sure you get the right thing.
posted by epanalepsis at 10:52 AM on May 7, 2012

Make sure the threads aren't damaged on the frame, and use Loctite when you install the new bolt (or the new derailer, if it comes to that).
posted by twblalock at 12:42 PM on May 7, 2012

For what it's worth, the bolt that fixes the derailleur to the derailleur hanger is a metric M10 x 1mm bolt. You won't be finding one of those in your average hardware store.
posted by tim_in_oz at 6:33 PM on May 7, 2012

It will also have a smooth area to act as a bushing, maybe a groove for an o-ring, and another groove for a retaining c-clip. So, no, not a standard hardware item.
posted by werkzeuger at 9:39 AM on May 13, 2012

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