Originally Posted by
jlaw
I've read that the Duo Par derailleur was an expensive component with an evolutionary design in its day that allowed for wide-range touring freewheels - worked well but could be fragile. Yours will probably be fine for a long time.
Here's a little history of it:
https://bikeretrogrouch.blogspot.com...et-duopar.html
Originally Posted by
bikemig
The Huret Duopar is a good derailleur. Frank Berto loved them and wrote about them in Bicycling Magazine. They can take up a lot of chain that's for sure. You should never change gears under a load with any derailleur but with this one, you really should baby it a bit by lightening up on the pedals when shifting. If you do that, you will get a lot of mileage out of it. I used one when I toured across the US and it worked great.
I'm one of those people that hate the Duopar- Starting with the Eco on my 620- and the Titanium on my 720. The hate of a thousand suns.
I wanted to like them- I thought they looked cool- in that industrial sort of way. My 620 was fine for a while until I started commuting. I kept having problems with the chain coming off the upper jockey pulley and between the cage and the pulley. It happened out of nowhere and once it went... it kept getting worse and worse.
The Titanium on my 720- I used it in conjunction with the Helicomatic- even though that thing had straight, square teeth- I swear I've never felt shifting that smooth. Like seriously not knowing that the shift actually happened until I felt the resistance on the pedals change. All that changed on one ride about 15 miles away from home- I still don't know exactly what happened- but what I think ended up happening is the stop spring ended up on the wrong side of the pin on the cage. It was a cluster****. I think the very next day I replaced it with a Deore XT.
If I were to get another bike that had a Duopar on it- I would replace it immediately. There's seriously no need to play ****-**** games and taunt fate. One of our esteemed members here tested out a 1985-ish Suntour XC with a triple pulley cage- it handled a freewheel fine up to 38 teeth. (
38!). XCs are easily overlooked, they're usually cheap because no one knows what they are- and the triple pulley models are, frankly, weird looking. And best of all- the XC is perfectly in the time frame of the 84 and 85 Trek 620.
*I really should add that many, many people have had exemplary experiences with the Duopar- including people that I respect and have much more experience than me and have more experience based knowledge than me.*