univega.duder

I'm a long time lurker but new poster. I'm not sure this is the best category to be posting in but am hoping someone may have suggestions for my broken derailleur dilemna.

I've recently mangled the derailleur on my Trek 720. I shifted slightly too far and the derailleur got caught in the spokes of my rear wheel. I immediately stopped but the poor thing seems broken beyond repair. Fortunately the drop out appears to be fine.

The derailleur is a Sachs Huret Titanium Duopar. I've been hunting on eBay for the last few months but have had little luck locating a replacement. I've only seen one for sale and it's missing some parts.

Does anyone have suggestions on where else I could find this derailleur? Or can anyone recommend an alternative replacement? I'd like to use something that matches the period of the bike. I'm fond of the titanium Duopar - it was shifting wonderfully and seems to be a really nice bit of engineering but perhaps there's something else that would be equally nice? Thank you in advance.

bikor 

That's unfortunate! Beautiful 720 there.

I've been musing over replacing my 720's non-original Acera 8-speed RD, trying to figure out what with. So far was thinking Duopar Eco, as I haven't seen the titanium model available anywhere either.

Saw this thread recently with some RD opinions starting from a Duopar viewpoint. Might be of interest if not previously lurked:
Help with Trek 728 and aging Duopar

The Golden Boy 

Hi- I have a 1985 Trek 720- very much like yours.

This is the bike getting overhauled, shortly after I got it:

John's Bicycle Restorations: Dave V's 1985 Trek 720 Overhaul - A Holey Grail Touring Bicycle

Here's the bike with an assortment of red Cannondale bags:

720 W/ Bags by Dave The Golden Boy, on Flickr



I rode the bike with the DuoPar for... about a year. Let me back up a touch- I also have a 1985 Trek 620 that had a DuoPar. I had a nightmare of a time with that derailleur- since changing it out, I've had no problems and pretty much zero desire to put that derailleur back on. I do not have faith nor confidence in the DuoPar to put it back on any of my bikes. Going back to the 720... I rode it for about a year- at one point I was shifting to come to a stop- the derailleur started dancing around like the one on my 620 did. I had to futz with it on the side of the road for a while. My best guess is I somehow pulled the lower arm through the spring...effectively turning it "backwards." At that point, I was like "**** that... DONE." Since then, I have had, quite literally, a dozen or so different rear derailleurs on this bike. I've had Shimano Crane, MT-60 Deore, M735 Deore XT, Suntour LeTech, XC 3 Pulley, a few different XC Pro, XC Comp, 2nd gen Mountech, V-GT Luxe, Cyclone, Cyclone MII... I'm missing a few in there...

Right now it currently sports an indexed 10 speed system with a Dura Ace 7803 long cage derailleur. It's awesome.

IMG_1715 by Dave The Golden Boy, on Flickr



The truth is you can use pretty much any derailleur you want. From a "working well" standpoint, you're going to need a long cage derailleur to take up the chain slack with the range you have for your chainrings/cassette/freewheel.

My opinion (which is as close to the most educated and esteemed professional opinion in the universe.) is that you should use a high quality, classically styled derailleur. Old ATB derailleurs from the 80s are fantastic. IMO- they're the coolest- they combine badass styling with a graceful classic style and have a long cage to take up the chain. Keep in mind, the 720 was the flagship bike for Trek. It came with the best components available at the time. I think the DuoPar was chosen because it had a great reputation. IMO- there were a LOT better derailleurs available at the time, and you could say even better in a few years.

If I were to go to a friction setup on my 720, I would choose the 1985-ish Suntour XC triple pulley derailleur.

Suntour XC by Dave The Golden Boy, on Flickr

Suntour XC by Dave The Golden Boy, on Flickr


My second choice would be one of the circa 1990-1994 Suntour XC Pro derailleurs.


Whatever you do, IMO, you should choose a high quality derailleur, befitting the status of your bike. IMO- you should not put on a modern derailleur with modern styling. It'll function great (maybe even "better" than any 80s derailleur) but I think it cheapens the look of the bike-


Here's the 720 with an XC Pro on it:

IMG_5422 by Dave The Golden Boy, on Flickr


And 2nd gen Mountech:

IMG_5975 by Dave The Golden Boy, on Flickr


I'll have go digging for pix of the bike with the XT and the LeTech... I don't think I have pix of some of the others like the Cyclones...


If you'd like other options- I'm MORE THAN WILLING to share my not so humble opinion.

oddjob2

^ +1 @The Golden Boy’s advice is spot on.

jimmuller 

I have nothing to add about the derailleur choice. But in that first pic I'd say your chain is 2 links (1 inner, 1 outer) too short. Don't forget, in order to shift the chain has to ride up over the teeth, which means it needs to accommodate an even larger radius. If the RD's take-up capacity is a limiting factor, better a chain too long than too short. A chain too long will simply dangle on the small/small combination, but a chain too short can break the RD on the big/big combination.

Salamandrine 

I pretty much second all the advice Golden Boy gave. I'd most likely go for a roughly contemporaneous Suntour. 3 wheel XC sounds ideal. I'd be happy with a simple Cyclone as well.

Never was that impressed by the Duopar myself. Fairly problem prone compared to other RD of the time. This is coming from someone who defends Huret Allvits and Simplex plastic derailleurs, BTW. Of course, they have their fans. Duopars were relatively rare, especially the Ti version. You would have a rough time finding a replacement, but it could be done if that's what you really want. What is wrong with it exactly anyway? If nothing is actually fractured, it may be repairable.

IMPORTANT: Almost certainly the derailleur hanger was bent when you dumped the chain. The hanger will need to be realigned. It will never shift correctly if this isn't done. If you don't have the tool, it's worth it to take it to a shop or coop that does. I suppose a tool could be improvised from a spare hub or something. Also, check the spokes on the drive side. If they are mangled, consider replacement.

I should note that a properly adjusted rear derailleur should never be capable of shifting the chain into the spokes.

Road Fan

I don't see any damage, actually. What is the damage? A titanium Duopar is a rare beast - it would be nice to keep it functioning.

jeirvine 

I'd vote for a Suntour Cyclone or Vx-GT. If you want to go the DuoPar route, I've have a (non-titanium) spare.
-John

Road Fan

Jim, in principle you're correct about the chain being too short and too long, but his problem should not have been due to insufficient capacity of the Duopar. With the vertical parallelogram and the long cage it has a really large capacity - Berto claimed they were 36 tooth max sprocket and 36 tooth wrap up capacity. Not the biggest, but pretty good.

OP: If you adjusted your limit screw correctly and the derailleur didn't actually break a pivot or rivet or something, the derailleur should not have gone into the spokes.

A common problem is that if you do not have the deraileur well-lined up with the chosen sprocket and you pedal backwards or roll the bike backwards, you could derail the chain and risk jamming it. If you then don't clear it before riding, you can break the derailleur. I've had a Duopar on a Trek 610 and before that a Woodrup tourer, and I've managed not to crash the derailleur, but I've also been really quick about stopping before damage occurs.

Road Fan

If you are ready to give up on your Duopar, I would buy it from you for parts.

An old SunTour would be a very functional replacement, as would a Campagnolo Racing Triple of any grade. I've had very good results with them on touring and sport-tour setups. But be careful to have enough chain links - your Duopar does look over-extended, and even a Campagnolo or Suntour needs to be fitted correctly.

Bianchigirll 

Welcome to the forums! Some of these guys are gaga, not the Lady type, for Treks.

Too bad about your RD. Any chance you can salvage parts from yours to fix the one on eBay?

I didn’t comb through all the advice but I would just put an older good condition Deore on it and call it a day. The slant parallelogram design and centurion pulley will give much better shifting.

JohnDThompson 

Ouch. That's too bad. While a titanium DuoPar may be hard to source, there are many perfectly acceptable alternatives as mentioned above.

If you do decide to retire the DuoPar, let me know if you'd be willing to sell it. I can use the parts here.

wrk101

Vx GT, best touring rear derailleur from that era, and very affordable. No brainer IMHO. Sell your broken one for parts, it should pay for the Vx GT with money left over for the beer of your choice! The triple pulley Suntours are really sweet, but a nice one will cost about 3X what you can find a Vx GT for.

Vx GT is period correct as well, and the standard friction touring RD out there. Priced right, top performance, looks good, durable, readily available. What more could you ask for? Whenever I build up a friction touring bike, I pull out a Vx GT to put on it. Once you get to the index era, Suntour's patent ran out, so everyone copied their design. I prefer one of the late 1980s Deore LX/DX/XT models instead.

+10 Chain is on the short side, which is dangerous. Once the derailleur goes into the wheel, need to have the derailleur hanger checked, very likely its bent. Simple repair by any competent bike shop. +10 a chain that is slightly too long only means it dangles a little when you are in small/small. Thats a combo you should never use anyway, and it doesn't hurt the bike. A tad too short and you risk major damage. Put me in the slightly on the longish chain side.

univega.duder

Thanks Bikor! Let me know what derailleur you end up going with. And thank you for the link to the related thread. Super helpful!

univega.duder

Hi Golden Boy- Thanks for the excellent response.

Wow your Trek bike looks amazing with the complete assortment of Cannondale bags.


It seems like you've tried a lot of options. I think your current Dura Ace 7803 looks quite nice. This may be a silly questions but would that also work in friction mode?


That Suntour XC looks great - did you add the red pulleys to match the bike?

I agree. Thank your very thoughtful reply!

univega.duder

I'm going to have my shop double check to see if the hanger needs any realignment. Thanks for your suggestions!

univega.duder

Thanks so much - I'm going to have my local shop check out the chain length.

Thanks I'll check out the Deore options :-)

I was just looking at this Campagnolo Racing Triple. Do you think this might be an appropriate fit?

bargainguy

I had a 720 with a DuoPar RD that was giving me all sorts of problems. Replaced with a Deore XT, much better.

Salamandrine 

It isn't obviously bent, so that's a good sign. But you can't really tell until you spin on the tool. I hope shops don't overcharge for that sort of thing nowadays. I'd imagine it's a rarer skill than it once was. Often about a 60 second operation total...

I pulled out a Duopar from my parts bin to check on that possibly bent piece the arrow points to. They seemed to be stamped that way. I don't think it's bent, at least not by a lot. You can tell by sighting the jockey cage from the back. It should be plumb vertical and parallel with the neutral chain line (after ensuring hanger is aligned). So, it might be possible to fix it, if you can get a replacement for the broken piece, if you wanted to go that way.

Other derailleur to consider is a Sachs/Huret from 1990 or so. These were pretty similar to Shimano RD of the time. Like everyone else, they adopted the Suntour slant parallelogram as soon as the patent expired. That Campy looks good too, but I wonder how much chain it will wrap, being a 'racing' triple? Certainly nothing wrong with Deore XT from that time either.

jimmuller 

Understood. I wasn't saying that his problem was caused by too short a chain, only that it was too short and could cause yet another problem. Some people tell themselves that they'll never shift into the big/big combination, and then a year later BOOM! they do accidentally. Better to prevent it before it happens than after.

In fact, we don't know if his Duopar could handle the big/big combination. (OP, are you listening?) I know it isn't likely, but a RD could have a 100T take-up capacity and the chain still be too short. The small/small combination might be 75 teeth within the RD capability limit, but the big/big doesn't have to be. In that pic the RD was stretched out dangerously far.

But now that you mention it, it is possible for this to cause the RD to be pulled into the wheel. When the chain catches the teeth at the bottom of the sprocket the rider's legs are pulling that chain HARD and thus stretching the RD with a lot of force. If it hits the RD's limit either the chain will come to an abrupt halt or the RD will break or bend. An abrupt halt is very unlikely because leg strength and momentum are pretty danged significant. A rotation stop (the B screw) on the RD may break. Or if there is the least bit of lateral flex in the cage it could deform the cage sideways. I'd guess you have a 50/50 chance of the RD bending to the inside, and if it does then it has a 100% chance of catching the spokes, seeing as how the clearance is pretty small. A post-accident analysis will show that the cage caught the spokes and the whole thing got bent out of shape. But the why isn't always that the low-gear stop screw wasn't set right. The seemingly obvious explanation is that the spokes caught the cage and bent it. But the cage could have been bent first, which is how it got into the spokes at all.

Trust me, I've been there. Once on a commute home in the dark on a rainy night 15 miles from home, chain suck from a small-to-big front shift jolted my crank to a stop, but after a what-the-heck moment and a retreat back to the small ring I was able to continue with no obvious trouble. When I shifted to the big ring a few seconds later I went down onto the road hard. Examination later showed that the B-screw stop had broken off. But the wheel would have pulled the RD backwards, not forwards, so that wasn't what broke the B-screw stop. The only possible cause was that chain suck a few seconds before had broken it. This would have let the parallelogram rotate too far forward, thus letting the cage rotate backwards beyond horizontal. When I shifted to the big ring a few moments later the tension pulley didn't move forward by moving down but apparently moved forward by moving in a sideways arc. Guess which side it moved to. Yeah, inside. Spoke catches cage, cage bend all out of shape, wheel comes to a sudden stop, rear wheel skids, Jim goes down hard. On the surface it was just a bad low-gear stop screw, except it happened on a front shift and I know how to adjust a RD, thank you.

Anyway, the point is that too short a chain or anything else that deforms the RD could cause it to get in harm's way, meaning to get in a spoke's way.

After all that... I would suggest the Vx-S rather than the Vx-GT. It's an intermediate length cage that most people would describe as long and considerably more available (i.e. cheaper) than a Vx-GT.

The Golden Boy 

Thank you!!! Almost as excellent as yours with the awesome matching racks and all 3 bottle cages! (I swear I have 3 of those blue cages around and I can only find one.) And your bags all match- my fronts are the "lightweight" models- more "nylon" than "cordura."


Thank you! These really seems to be the last of the "classically" styled modern derailleurs- the Dura Ace 7803 and the Ultegra 6603 (along with the 105 5503). Yes- they'll work great in friction mode. That being said... If you're running all "vintage" stuff, I'd kind of want to stick to the more "vintage-y" options, rather than the one "new" thing sticking out. (again, with that IMO stuff)


Actually, I added the red Bullseyes solely to stand out. . I like the idea of bearinged pulleys- I don't know how much of a difference they actually make, Bullseye made some kooky wild claims of the energy saved vs bushinged pulleys... In those pix, I actually have a "titanium" colored Bullseye pulley for the jockey, and even though the farthest out pulley is usually not engaged, I wanted the two "show-y" pulleys to show.

The 3 pulley derailleurs do take up a lot of chain- without a LONG cage swinging about. And this unit does shift amazingly well.


Thank YOU!


An important thing to remember- don't trust modern shop guys to know about "vintage" stuff. Their inclination is to get your bike working with as little fuss as possible.

Here's a couple of pix of my Duopars, let me know if you'd like some other pix:

Sachs/Huret Duopar by Dave The Golden Boy, on Flickr

Sachs/Huret Duopar by Dave The Golden Boy, on Flickr



The derailleur stop is built into the tabbed washer- you'll see them zip tied onto the derailleurs- they're unique, and pretty much impossible to acquire if yours gets lost or broken. Again, let me know if you'd like pix.

univega.duder

Thanks for the pics - those are really helpful. I'm going to take my broken duopar off the bike for closer inspection. I just ordered a chain tool which I'm excited to learn to use.

univega.duder

Hi Jim- Thanks for the details and suggestions. I've been doing my best to avoid the big/big combination though I'm certainly not a super experienced with my shifting skills.

Thankfully I was going very slow when the derailleur was caught in the spokes and I was close to home. Your derailleur incident certainly seems a bit more dramatic. I think mine had something to do with me rolling the bike backwards before getting on it. In any case I'm going to checkout the Vx-S and have my shop check out the chain length. Thanks you :-)

univega.duder

Excellent suggestions - thank you!

Thank you for the safety tip. I'm going to ask my local shop check out the chain length.

univega.duder

Thanks for sharing your experience. I'm a little spooked on the duopar after breaking it and am looking forward to trying some else. I'll take a look at the Deore XT.

Beautiful Trek btw. I like the yellow accents.