bikemig 

I'm thinking about picking up a 1990 Schwinn DuoSport Tandem that is available locally. I've never owned or ridden a tandem. I had a few questions:

(1) The bike has u brakes with the rear mounted under the chain stays. Not my favorite design for an ATB bike if used off road but seems like a good design for a road bike. I know cantilevers are more common on vintage tandems but this seems to be a good design. Any reason to be concerned about this?

(2) I've bought my share of old bikes before but never a tandem. Is there anything in particular I should look out for in inspecting the bike?

(3) I have no idea about pricing. The seller is asking $450 but the bike at a minimum needs new tires (choices will be limited since these are 27 inch wheels, Schwalbe marathons run $43 apiece), brake pads, cables, a complete overhaul, and I wouldn't be surprised if the crank spindles need replacing. I can do all the work but it needs well over a $100 in parts.

(4) The size looks ok at 23/21. 23 is a good size for me; it's a bit large for the stoker but given the mixte rear that should work. Is the stem for the stoker something more or less standard and/or readily available if I need to change it?

The retrogrouch has a nice write up on this bike here,
https://bikeretrogrouch.blogspot.com...rt-tandem.html

All in all seems like a nice vintage tandem.

Leisesturm

Schwalbe Marathons come in 27"? Hmmm. I was initially "No, hell no!" This did not seem like a good buy on its face. The linked review by Retrogrouch adds nuance and insight so I have softened my knee jerk response to a "maybe ...". It all depends on what you want. If its a bike to ride twogether with someone, I for one would look for a Burley or Trek in the mid to later 90's. Even a Trek T900 from the early to mid-2000's. If you already have a tandem and want a vintage example to restore ... maybe. I'm not sure you will be able to get the price much lower but you could certainly try.

WheelsNT

A little more information would be helpful. What are your goals for this bike? What are your expectations? What level are your other bikes on and how do you want a new tandem to compare? Any idea how many miles you want to do, per ride, per week, etc. How fast do you ride on your single? You get the idea.

bikemig 

No big plans for the tandem other than to ride the local trails. There are no major climbs but there are plenty of rollers. No particular speed in mind but I do plan on being able to do some longish rides on it (say north of 50 miles). My racing days are past me so I'm not worried that this is old technology.

I'm a fairly good mechanic but I've never worked on a tandem or even ridden one. So I'm looking for some advice before buying a used one.

L134 

1) Not that I'm aware of.
2) How is the timing chain tensioned on that bike, eccentric? Is it frozen?
3) It is not like $450 is a whole lot of money but I would expect that bike to be completely serviced and ready to go at that price. Here in Southern CA there would be plenty of better options at that price but maybe not where you are. I think it sort of depends on whether or not you are looking for THAT bike (then go for it) or if you are just looking for any decent tandem for casual riding and how often they come up where you are. If rarely, go for it. Either way, if tandem riding doesn't work out for you, you will probably either have to be lucky or very patient if you want to sell it.
4) As long as the stoker seat can go low enough for the stoker, the frame being a bit large shouldn't be an issue. I believe different stoker stems shouldn't be a problem. Check out Tandems East, I think they even have adjustable stoker stems.

WheelsNT

Ok, so you're not just going to use it for half mile rides to the ice cream shop. In that case if it was me I would want something better. Of course you're not "me" so you may evaluate differently -- let me itemize some of the factors that lead me to that thought:

A) It's a steel tandem with a mixte frame, no lateral.... I think it's going to be pretty flexible in spite of the oversized tubes. On a tandem you have to contend with two people moving around in different directions. The captain has to compensate for those movements with steering inputs. The more flex in the frame the more complicated that gets. Now there are people that happily ride mid-70's Gitane and Motobecane tandems that have even skinnier tubes than the DuoSport, so if you like vintage stuff and flexible frames then no problem. But I think I'd want something stiffer, especially as a new tandem captain, to simplify your task.

I realize I didn't ask for your team weight -- "Team weight" is the sum of the weights of the two riders. The higher that is, the more important (obviously) frame flex will be.

B) The modern standard for tandem rear dropout OLD is 145mm. The DuoSport looks like 6 speed, so it's certainly not 145mm. Might not even be 140mm, could be 126mm or something. Narrower OLD equals less bracing angle on the spokes, which forces higher spoke tensions, which leads to broken spokes. 70s-80s era custom tandems often had a braze-on to hold some spare spokes on the frame, because spoke breakage was a common occurrence. Wider OLD hubs mostly fixed this. In any event, anything other than 145 will make putting new wheels on it in the future more complicated. This is important because...

C) It's probably a freewheel rear hub. The changeover from freewheel to cassette was no big deal for single bikes but was huge for tandems. Tandems with freewheel hubs tend to break rear axles because the bearings on the drive side are too far inboard from the dropout and the axle has to span the distance. Cassette hubs fixed that problem, I don't think tandems with cassette hubs break rear axles any more than single bikes do.

D) No brifters. Being able to shift and brake without moving your hands is really helpful on a tandem, and particularly for a new captain. I'm not against older stuff, in fact my single bike is older and has downtube shifters that I have no issue with. But having hands on the bars at all times is helpful on a tandem to counteract unexpected movements by the stoker. So if I had a new-to-me tandem, I'd be looking to add brifters as soon as I could. On this bike that's going to be complicated by the OLD. If you had 145, you could put any modern drivetrain on it you wanted.

E) Quill stem. This is not a huge deal, you can always add a quill column and put your modern stems on that, but it's heavier, and a newer tandem would be more convenient.

So I see I gave a bunch of ideas but haven't directly answered the questions you asked.

1) U-brake -- no particular issues, but you should probably replace all the brake shoes right off the bat. Tandems are harder on brakes than singles as I'm sure you are aware.
2) Look for frame and fork cracks, especially fork crown area. Look for cracks in the hub flanges laterally from the spoke holes, and look for rim cracks near the eyelets. Tandem wheels are (should be) built with higher tension than single bike wheels, so there's a higher incidence of cracks.
3) I think of a tandem as two single bikes worth of price. So if you buy a tandem for $450, that's two single bikes at $225. If $225 is less than you would normally pay for a single bike you would want to ride, then consider spending a little more for a tandem.
4) Adjustable stoker stems are available....(for example) https://www.ebay.com/itm/193647814428 Be careful about the seatpost size as well as the handlebar clamp size. You may have to use shims on one or both to match what the bike already has. Shims are not a problem if that's what you need to do.

Hope that helps!