I don't really recommend this derailer, though I used to love them. When they first came out and for a few years afterward, I put them on a couple of my own bikes, and on the expensive "boutique" custom bikes I was making for customers. They shift great until they don't, which can happen depressingly soon after buying. I had some unhappy customers who blew up their DuoPar by either pedaling backward with the cage not aligned under the cog you're in, or backing the bike up, or.... Lotsa ways to bend one.

I warned people about this, but it can happen even to people who've been warned. Even to me -- after having seen lots of my customers break theirs, and being VERY familiar with the quirks, I still managed to break mine. I was finishing up lunch in a beautiful piazza in some Tuscan hill town as some of the slower members of the group rolled out first to get a head start. As they went around a corner and out of sight, I heard a crashing noise, sounded like bikes hitting the cobbles. I ran to my bike, did a cyclo-cross running mount and started to pedal hard -- but all I succeeded in doing was to bend up my DuoPar. Someone else had bumped the shifter while the bike was parked, and the mech wasn't lined up with the gear I was in. Yes even pedaling forward can bend one up, if the chain has jumped off the upper pulley. Ironically and luckily, no one in my group had crashed, never did find out what the crashing noise was. Oh well. I limped down the hill to the next valley town where I bought a cheap Shimano that allowed me to finish the trip.

I sort of swore off DuoPars after that, though I still think they're beautiful in their way.

There are some things you can do to reduce the tendency of the chain to jump off the pulley. The main problem is the inner cage plate doesn't extend up high enough. So I made a new inner cage plate, using a part of a Suntour Cyclone cage, see here:


I wish I could claim I invented it, but Angél Rodriguez showed me how to do it in 1979.

This mod has the added advantage of opening up the cage so that, like on classic Suntours, you could take the chain out without removing a pulley or a chain link.

Angél used to replace both pulleys with Suntour sealed while doing this mod, but that's more work and I'm lazy, so I only replaced the bottom one.

Oh and in case you were wondering, the one I bent in that Tuscan hill town did not have this mod. I think it would not have bent if I had done the mod, but I left for Italy in a hurry and threw this DuoPar on my racing bike at the last minute to put some lower gears on.

There's another issue, that comes up with hubs that put the small cog very close to the frame, which is good for minimizing wheel dish. French frames and hubs were designed for a bit more room there, but if you use a Campy or Dura-Ace or other high-qual, dish-optimized hub with minimal space there, the derailer has to be adjusted further out than it was meant to go. (Damn Frenchies!) What happens is, the second (up/down) parallelogram can't pivot all the way up when in high gear (small cog). It hits on itself, one of two ways: (1) If you shift into high first, before the up/down parallelogram has a chance to swing up all the way, no big deal, the jockey wheel just won't be in the optimal position close to the cogs. However (2) if the up/down parallelogram pivots up first, then you can't shift into high. Causing you to lose the sprint! Or you get dropped on the downhill by that tandem you were trying to draft. Whatever, it's got to be fixed.

Two places hit, and you just need to remove a little metal in both places.


For the place, in the upper red circle above, I dremel some off the upper Ti knuckle and the steel back plate of the main parallelogram. A small round file could also work. You'll see once you start filing, at first you're taking metal off the Ti knuckle only, but then you go a little further and you're nicking into the steel a little as well. Just take off as much as needed where it hits. I could have removed metal off the 2nd parallelogram instead, but that place is fragile. The place I removed metal has plenty of "meat" even after the amount I removed. Makes you wonder why Huret didn't do it... For where to remove metal for the other interference point, the lower red circle in the photo above, keep reading.


First I want to point out the upper red circle in this photo. It shows another view of what I talked about above -- where I dremeled some off the upper Ti knuckle and the steel parallelogram. This shows how there's plenty of metal there, so I didn't hurt it at all, it won't break there.

Now let's look at the lower red circle in the photo above. You can see a hint of rust where I thinned that tab, that the parallelogram spring pushes against. I just took off a little, and on a taper, so it's still full-thickness (see the chrome?) where the bending force from the spring is at a maximum. Taking some off there means not having to take quite as much off the final place, shown in the next photo.

Take some off the black lower arm of the 2nd parallelogram. See the bright bronze circle? Turns out that black arm is bronze, who knew? The bright bronze circle is where I removed about .5 mm to maybe 1 mm. Just take off metal as needed until it doesn't hit anymore. In a regular unmolested DuoPar, the steel axle in the center of that bright bronze circle would protrude, and would need to be shortened a bit too. This would cause it to rust, so dab some grease on it and let it get grimy. On mine, due to the cage mod (first photo in this post), this steel axle is slightly recessed there, so it didn't need to have its chrome plating disturbed at all.

So, all of that trouble just to make it work the way it should have out of the box. I wouldn't blame you if tossing the Duo-Par and putting a V-GT Luxe* on there is looking more sensible.
* or Cyclone GT or Crane GS or Simplex or almost anything else... Even <shudder> a modern indexing derailer.

Mark Bulgier
Irony Cycles
Seattle