While working on the Fuji TSIV, the spring in the rear derailleur, a GT long cage, gave way. I pulled it apart and sure enough the "anchor" pin of the spring snapped off. This is the part of the spring that anchors into the body of the RD to provide tension for the cage. Does anyone know if a short cage Cyclone RD have the same spring specs as the long cage? There are a few short cage RDs on Ebay but not a long cage.

Short cage springs will work. I have also bent a new pin onto a broken spring. I think I used needle nosed pliers and a vise.

Dimensions are the same, but I think the spring tension may be different.

I've done this exact thing, and for the same reason. As you note, the short cage Cyclones tend to be more common or less desirable, and therefore lower cost.

I'm still trying to figure out how to predicts when those springs will break or why. It can be a problem when it happens on the road.

oh... just to be clear, I'm talking about the first generation of the Cyclones. The Mk II Cyclone springs break too, unfortunately.

Steve in Peoria

Jeirvine, I tried to do the same unsuccessfully by hand with a pair of pliers but didn't pull out the big tools last night. I was looking for the quick fix last night with the pliers in my exasperation of a small job all of the sudden turning into an "Ouch, That's Going To Cost You" moment. Nothing to lose with mangling the existing spring a little more so I'll this a shot since I slept off my "internal tantrum" last night.

Steve, mine is a 1st gen derailleur also. And, I wish I could have predicted this spring's demise. I was simply re-pinning the chain after waxing and was pushing the RD forward for some slack when the RD tension went slack and forward in my hand. In that split second after the spring gave way, I paused without turning my head and hoped that what my brain was telling me "what-just-happened" really "didn't-just-happen".

I gather it is only a matter of time for these springs to break and I should start now procring a donor? The spring on my lightly used GT came unwound during a ride when the pin came out of its anchor point in the derailleur body. I expected to find a broken spring but the pin was still there only not bent at what I assume would be the proper 90 degrees. I could not manage to get it all back together with the pin like that and took a chance straightening the pin. It's been working fine since, but maybe this is not the derailleur to use on my 20 mile commute?

Like all things vintage, parts do give out. I've had it happen on other bikes and old cars that I've owned. It's very possible that I unwittingly accelerated the demise of the spring by pushing it too far forward for its age. However, after nearly 40 years of use, there had to be some wear on the spring that didn't tolerate the distance I pushed it. For my bikes, I rather have the parts original or close to it. I enjoy the look and feel of those friction and early indexed components. Plus, their simplicity allow me to work on them (assuming I can bend a new straight pin on this #$%^@$# spring!). If a part breaks on a ride rendering me stuck on the side of the road, it's not a disaster since my riding buddies will help me out or the wife is a phone call away.

However, if the pin on your RD has already started to bend away from the original 90 degree orientation from normal use, then I would think its days are numbered. It doesn't mean that you can't have a "hack" ready in the saddle bag to hold the RD in a reasonable gear to get you home if the spring does give way.

However, with that said, if I was depending upon a bike to commute to work, I might save the vintage bikes and components for the weekend and have a newer commuter that was dependable and reliable. I use to drive an old BMW to work which was fun until a fuel pump or alternator brush would wear out half way home. Now I'm driving a Toyota Highlander which doesn't have the same fun factor (if any) of the BMW, but dang having the piece of mind knowing that it's going to get me 40 miles down the road and back without worrying is priceless.

My Zero Bike has a 1st gen Cyclone GT on it. After seeing [MENTION=111144]Andy_K[/MENTION] break a SunTour spring while riding, and others report here with the same issue, I brought a spare rear derailleur on Touroica this year. I was worried that it would break somewhere on Hwy 1 in the Big Sur area. Now I'm thinking I should just swap it out, since this bike gets used on credit card tours in the Bay Area once or twice a year.

I wonder if there's a way to stress-test these things. Like, a jig with holes for the pins that you turn to wind up the spring as much as it could go in service, then another 20% or something like that...

They are pretty mechanisms. I think I'll put mine on the shelf next to my shiny Pfleuger Rocket and use a later Shimano unit.

I'm pretty sure I've related the tale of my spring breakages somewhere in the last year or so.
The first breakage was maybe 3 years ago, with the bike in the workstand. Like your situation, I was just moving it through the usual range of motion and suddenly a little snap and the chain went limp. I had spare derailleurs in the parts box, so not a terrible thing.

The second time was on a different bike and about three miles into a ride. I was riding on a flat stretch of road, not shifting or hitting bumps or anything. All I knew was that the rear wheel locked up and I skidded to a stop. The rear derailleur looked like this:



The fact that the pulley cage is pointing down, despite the chain having left and gone off to jam in the spokes, is a hint that the spring broke.
I won't bother showing how the chain also jammed in the front derailleur and bent it all up (and I won't mention that it was a lovely Campy SR front derailleur either. )
The chain was so jammed in the spokes that I couldn't pull it out, and I didn't have a chain tool, or I would have cut the chain so I could at least roll the bike. As it was, I had to carry it on my shoulder for the 3 mile walk home.

I took pics of the broken spring, but I didn't come to any conclusions about the cause of the failure.





I've been using Cyclone GT's since they came on the market in the mid 70's, and it took over 40 years to see my first spring break. Not sure if this means that they are all running on borrowed time, or if it is just random. I've had a very similar spring break in the same way on my SunTour cantilever breaks too, so it might an issue with the production processes. I've seen spring problems at work, where there were some subtle indentations from the bending tool that led to breaks at that spot. Any stress riser can be a problem, and I didn't have pics of the springs before the failures.
With that in mind, I did take some shots of the new spring that I put in the last derailleur. No obvious stress risers, and the simple act of paying attention to it might keep it from failing (fingers crossed).




Steve in Peoria

How difficult would it be to produce a run of reproduction springs? It seems like a small but eager market is brewing. One could hope to become a break-even-aire.