SunTour Front Derailleur issues
 

Greetings..

I have not posted in a while as I have had other things going on. However, I have been working diligently on the 1981 Centurion Super Tour 15 I obtained at a garage sale and have basically made it ridable again. As I have come down to the final adjustments it has come to my attention that POSSIBLY a previous owner altered the triple chainring by adding a very small inner ring for very low speed climbing but left the original front derailleur on it. When I got the bike the whole section that moves the chain side-to-side was literally torn off and I wondered how that could have happened. Fortunately, I found an exact replacement on eBay and mounted it up but the same situation came up for me - the chain drops so far down on the lowest cross-ring that it rubs on the rear cross-piece. Possibly the thought was to remove that cross-piece entirely resulting in the shifter being caught in the chain???
The difference in diameter between the large and middle rings and the smallest is considerable. Is there a derailleur that would better shift to all three or can I 'modify' this one to work?

Thanks in advance for your suggestions!

Wil

What model is the Suntour derailleur? Some of them had extensions available for the cage to deal with your problem. An alternative might be a larger small ring. You might find the latter easier to find.

...Or a smaller large ring; whatever it takes to reduce the difference between the two.

But first of all, make sure you have a front derailleur that's intended for a triple (a longer cage that curves down farther is the most obvious feature). Some FDs made for doubles can work with some triples, but it depends...

Here's a Velobase listing of the Cyclone FD with the cage extension: VeloBase.com - Component: SunTour Cyclone (with no cable housing stop; with wide cage extension added)

You can often find the part on ebay - here's the screw that replaces the rear pin screw - http://www.ebay.com/itm/like/31018426493

http://velobase.com/CompImages/FDera...3EC703C86.jpeg

That said, I'm running a 46/42/26T Cyclotouriste triple with a Shimano 600 EX FD (my favorite FD ever) and it's fantastic. This is also with a Cyclone GT RD. The RD is short one link in chain wrap, but there is never a reason for me to go to the 12t cog in the rear and 26T ring in the front...
http://img.photobucket.com/albums/v7...0c/drive26.jpg

As I have mentioned in the past, bulldog1935 has the right idea -- a smaller outer chainring lets you lower your front derailleur, which in turn will increase the number of suitable candidate front derailleurs.

With 13 teeth in back, I really do not need anything bigger than about 46T in front -- I have 45 on the Peugeot, and 47 on the Capo MC. When the PKN-10 was mine, I installed a 48-45-34 triple with a 13-23 freewheel and the original road double front derailleur, all without any issues. My son insisted on a taller top gear, so I regeared it 52-45-34, which still works extremely well.

I'll show you how my half steps + granny works here

If you want to pick a new chainring, plug your cogs and chainrings into the gear analyzer, and try different chainrings. Pick a chainring size that will minimize overlaps and give you the most gear options - narrow steps between gears. Especially look at the semi-log graph for gear spacing and overlaps. If it looks evenly spaced on the semi-log plot, it's perfect.

(printed and scanned this, but the download didn't pick up all the details)
http://img.photobucket.com/albums/v7...935/Scan_2.jpg

Most likely the offset between the big and small ring is beyond the capacity of the changer.
You might have to look at a mtb. front changer. There are a few that were modified by the component mfgs. to accept super wide ratios, not the easiest to find.

The critical parameter is the tooth difference between the large and small chainring. Depending on the cage design, this can vary widely. Some of the boom era derailleurs handled as little as 14T difference but by the mid-1980s,some were capable of handling up to 26T difference.

Per previous requests, you should post the brand and model of the front derailleur and the size of the chainrings.

I'm running a 1sr gen Cyclone FD with a Stronglight triple. I think it's something like 52-42-28. It works perfectly , and I do not have the cage extension on it. From a lot of sources, the extension causes more problems than it's worth.

I like 53/52-42-28/26s. I have many times use front derailleurs where the chain dragged on the roller/spacer on the cross bolt. As far as I can tell, that drag causes no issues except rapidly wearing out the roller. My solution has been to get a stack of small washers and use them instead of the usually plastic rollers. It also allows me to easily customize the width of the bottom of the cage. (I like to narrow it down. Improves shifting to and from the small chainring. Yes, I have to trim the FD more, but that isn't hard with DT shifters.)

I did buy a new DA front derailleur 9 years ago building mu my custom to use with a 53-42-28. Even though it is touted for rather different (but still triple) gearing, it works better that anything I have ever used. A tough statement for this non-Shimano guy to have to make. (I did my research. The Ultegra was "right" for the chainrings I was running. But it had a dull brushed finish that would look just wrong on the bike, The DA was bright shiny chrome and looked "right". Amazingly, the good looks actually worked well.)

Edit: I would go with my washers and chain drag over the extensions every time. They strike me as both a place for the chain to hang up and an additional loss of stiffness at the flexiest part of the cage. The bolt across screwed tight with good spacers inside serve to turn the cage into a closed box from an open "U" and improves stiffness and lowers flex when you shift a lot. For engineers - think of the cage as a cantilever truss, one where diagonals cannot be used. The difference between solidly fixing, just pinning or completely removing the far end member will be large.

Ben

Is that the 7803?

I have no idea. Where does it say or how can you tell?

Ben

I'm sure that's true, not sure why I'm called out on this. Most bike boom triples are narrow-Q and were designed for road double FD. When you need a mountain triple FD is when you have a mountain triple crank.

It's also possible our OP has his FD mounted too high up the seat tube.
With the chain on the smaller ring (middle of a triple), the thickness of a penny should be able to ride the teeth of the big ring beneath the FD cage.

On my Pro Tour, I'm running a Cyclone MkII with a Sugino AT 52-42-26 triple. Without the cage extension, the chain drags on the end of the front derailleur. With the cage extension it works perfectly..so far.

Previously, I was using an XC Sport front derailleur, because it shifted better and I didn't feel like fussing around with the stupid banded-clamp on the Cyclone. At some point the bolt at the end of the XC cage came out and the cage did the taco on a shift.

Yeah, I'm one of those sources. I had a '76 PX-10LE that I'd built with an Avocet triple and Suntour F&R derailleurs in about 1979. The FD had this extension. My inner ring was a 32 and rarely used.

Fast forward, I sold off the Peugeot frame and moved the gear to another frame with an inner triple front ring at 28, and the same original Suntour FD with this extender cage.

In my anecdotal experience, it is about chain wrap tension. But, the chain will/did catch on that large inviting edge. I was able to vault off the bike w/o damage, but you can just rip that sucker up. If you're shifting that low, odds of a catastrophic crash are actually low, but you may be w/o a functioning FD.

Anyway, as much as I loved that FD for it's smooth working of the upper rings. . , it came off.

SO, I basically recommend against it. Focus on fine-tuning chain length and wrap strength of RD to solve the broader issues of small granny ring shifts.

YMMV, as it is said, and this is but one piece of data.

:-)

P.S. - If you particularly like Suntour, consider the 3-pulley RD for the touring gear set.

???

"Called out?"

You brought up the Cyclone cage extension.

In relevance to that topic of discussion , I just said that I, like many, many other people, have a 1st gen Cyclone FD working on a wide range triple without the cage extension and that many people have experienced problems with that cage extension.

There's no argument, no "calling out," or even disagreement. Just statement of fact relating to the topic you introduced.

no, it was CV-6 who brought it up - I just showed the component and the alternative
and I agreed with you, so I don't see the argument
the thread is not about either of us

call-out
noun
1.
an instance of being summoned, especially in order to deal with an emergency or to do repairs.
"a call-out charge"

I didn't know the MII Cyclones had a cage extension!

I also lost the screw that holds the cage together on an XC Pro FD. Go figure...

It's on the back-

http://i1294.photobucket.com/albums/...psur3u0tan.jpg





I'm interested because I've got this one, and I'm planning on using it on a non-Dura Ace triple.

My triple pulley RD is one of the nicest shifting derailleurs I've used. I honestly don't know if it's "better" than my XC Pro, but it sure works nice and it looks so unique. Pastor Bob had a 38T cog working with this. As fanciful as it is- it's all business.

http://i1294.photobucket.com/albums/...psnqjxdqbp.jpg

Thanks to ALL for your suggestions!
 

The derailleur originally on the bike was for a triple chainring group (hence the name Super Tour 15). As the actual changer had been broken off I can only guess that the one I found as a replacement was the same - a Spirt. The extension idea seems the easiest for me as I can either find one or make one as I have the tools (I'm a Jeweler).
I'll try to post a pic of her when she's done (if I can ever figure out how to get one small enough(?) to be accepted here:)

Ride Safe!
Wil

Mine's a 7703. Looks like yours.

Ben

The FD-7703 was the triple compatible front derailleur intended for the 9 speed Dura-Ace group while the FD-7803 was the triple compatible front derailleur for 10 speed Dura-Ace. FD-7003 was rated for a chain ring difference of up to 23T while the FD-7803 was rated for a 22T differential.

FWIW & AFAIK:

The Spirt (we all thought it was a misspelling, but apparently not) is a bargain secret that was reported to handle wide ring changes and triples surprisingly well. Not considered especially cool, but NOS samples come up for truly modest cost. I know I have one somewhere, but no photos.

It also shifts in the opposite direction, which seems to help with the wide jumps. Go with it!