roccobike

Right now, I have a Schwinn Suburban, a co-worker asked me to work on, sitting in my basement. When she unloaded the bike I checked the rear deraileur and was glad to see 'Shimano'. As I read further, I saw 'Positron'. Sure enough, this bike has the Positron system, pawl in the BB, and indexed rear deraileur. She claims to have purchased it in 1972, but I didn't think Shimano came out with the positron until the mid to late 1970s.
There is no shortage of steel in this Schwinn, it weighs in at a not so svelt 44lbs .
I wonder if any of the Schwinn experts would comment as to whether or not this is a desirable bike. I have no interest in it, but I think this lady would be better off selling it to a collecter and using the money for a new, relatively light weight, hybrid. I didn't have time tonight to take pictures, but if anyone wants to see it, I can take some on Saturday and post.
I plan on cleaning the chain and replacing the tires (with 27X1.25 Kendas). Is there anything tricky about the chain removal? It looks like a straight forward removal, but I would hate to be surprized while working on someone elses bike.

Little Darwin

There are no tricks to the chain that is different than a non-Positron non-FFS (Front Freewheel System?)bike that I am aware of.

As far as selling to a collecor, it is not likely to have much value. I bought a 1979 example with Positron II and FFS for $10, and the person had more if I wanted them.

If the bike is unique and collectible beyond being an old Suburban, it may be worth something, but unless there is something unique (like the first year or something), selling it would probably give you the money for a front derailleur on a new bike.

Just out of curiosity... Does the bike use a single solid "cable" or dual cables to the RD?

If the RD needs to be replaced, and uses a single solid cable, I have a Positron II you can have for the cost of shipping. I have a FFS crank in pretty good shape that is also available for cost of shipping. For a limited time only, I will offer both... for the low low cost of... Nothing, plus the cost of shipping.

And as usual lately, a non-obligatory request to donate a little to my LiveStrong Challenge ride.

rhenning

You can date the frame if you give us the serial numbers. Should be on the head tube. Positron was Shimanos first experiment at indexing and was at best junk. You are correct in that Positron came out in the late 1970s. I think it was 1979. Roger

jordanb

Nearly every hybrid made for sale today in the US (Bianchi Milano, Breezer, whatever) is based on mountian bikes. They have more aggressive riding positions than a comfort bike aught to have but the rider gains basically nothing from sitting hunched over because it's not so aggressive as to reduce wind resistance at all. Plus most don't even have springed saddles. And they're all aluminum. So except for the "weight" thing (mostly irrelevent imho) the suburban will be a more comfortable bike for her.

A suburban in good working condition will be worth something like $100 on ebay. Maybe $85 on craigs list.

No way is that thing a 1972. I don't even think Schwinn was doing buisness with Shimano in 1972.

teambhultima

My 1974 Suburban is a standard 10-speed. F&RD's are marked "Schwinn approved" (the approved is in tiny type), but I can't find Shimano written on them. Perhaps this will help date the bike you are working on. For what it's worth, I've found the Schwinn to be a comfortable bike to ride (slowly) even though it weighs a ton.
Best wishes.

roccobike

The serial number of the Suburban is CQ512636. The headbadge number is 0749. If someone knows the date of the frame, I would be curious to know. I'm not sure when Positron was first made available, but I know it was available by 1978. The 78 Raleigh catalogue offers two models with the Shimano FF system, a special Raleigh Record and a Rampar R-4. Thanks for all the information about the Suburban. Apparently these are quite common. Still it's an intesting bike. For the record, the Positron on this bike works VERY well, not one shift missed or sloppy. Actually, it shifts better than some of my bikes.

mswantak

Both numbers make it March 1979, so it's within the same time period as the Positronic.

roccobike

Thanks for the information. I will pass it along to the owner.