Phil_gretz

Okay, it's a curbside find. Really nicely painted Sears free spirit 10-speed with matching sprung seat and grips. Lots of chrome...

The bad part is the positron shifting system with a broken/frayed rear cable.

Two questions:
- is is possible to even find this cable?

- Does the presence of Positron mean that the front chainrings "freewheel"?

I'd like to make this bike at least rideable.

Advice (other than to throw it into the river by cover of darkness)?

fietsbob

They were not using cable, but a solid steel wire , instead,
so it was a push as well as a pull to shift.

you might try another cheap derailleur, and shifter.
cable pulls, and force of return spring pulls back
is the normal way most derailleurs work

bobotech

We had a girl who came into our shop and had one of those positron bikes. She ended up replacing her shifters, crankset, derailleurs (not sure if we did the front one), and cables with standard stuff. Works great now. LOL

Snydermann

The cable and or cable/housing assy can be found on eBay in the $20.00 range. Sometimes it's less expensive to use, and can be found as, part of a complete cable/housing/lever assy.

I've read that a lawnmower throttle cable can be used, but I have never tried it.

Positron does not necessarily have to use the Shimano FF (Front Freewheel) system, but they are found together quite often.

temon00

my answers to your questions: 1 Yes 2 Not Necessarily
I had a similar issue with a found bike. IMO, it's way better to try to get a used friction shifter setup. You can find NOS positron stuff on E-bay for about the same price as a set of stem-mounted shifters and a cheap SIS RD (if you are inclined to buy those things). Better yet, you may be able to nab the shifter/derailleur set off of someone's "broken" bike.

mechBgon

Positron, or Positron II? Pics?

You can have someone create a diversion, so you can throw it into the river in daylight instead

Jeff Wills

I've seen them on Ebay. Be aware that they are fixed length- trimming them is not possible. You will need to get the correct length to fit the bike.

Phil_gretz

Thanks everyone, and Jeff, I noticed that both ends appear to have housing terminations that are not to be cut. The existing housing is severed/worn, but I'm assuming that I can lay the two pieces down to figure out the original length closely enough.

I might go for the positron cable, or I might scrounge up a set of stem shifters and a Lark derailleur or somesuch. The frame has no cable stops anywhere - as full length housings ran everywhere. Fortunately, the front derailleur has a standard shift cable and has a return spring.

I can't seem to detect any freewheeling in the crankset, which is also a good thing, although the bottom bracket is a tad loose. I've never worked on a one-piece crank, but there appears to be a large hex nut on the non-drive side, which I'm assuming is the way to adjust. I dare not open it up (having read threads on this) but I'll try to adjust it to remove the side-to-side play (it's really slight, now).

Thanks for the input, guys. Last night I finally got my SD card back from the surly 19-yr old who lives in my house (daughter), who stole it two weeks ago...so can take photos again. I'll post before taking it all apart to clean.

I'm assuming that this is Positron II, just because of age (from looking at the Disraeli Gears links).

JohnDThompson 

Positron cables show up on eBay frequently:

https://www.ebay.com/sch/i.html?_nkw=..._from=&_ipg=50

mechBgon

The threads on the non-driveside are reverse-threaded. The large hex nut is a locknut, so loosen it with a clockwise turn, then turn the underlying cone counterclockwise slightly, snug down the locknut again, and reevaluate the bearing play. Repeat until optimal. If there's still some play even when the bearing starts to get resistance, it could be that the driveside cone (which is normal-thread) isn't fastened tightly, and is shifting around. If you decide to overhaul the whole thing, you won't need to know a whole lot more than that.

Sounds like it is, yeah. Positron used a dual-cable setup, Positron II used the solid push-pull single-wire setup. It actually was a good system for the casual rider, especially paired up with the front-freewheel system. Related tip: those Positron II inner wires will punch a hole in you really easily. If you don't have the special tip that's made for them, grab the end of the wire with a needlenose plier and loop it back on itself.

Phil_gretz

Thanks, mechBgon, I'll give it a shot. The bike sat in a clean, dry garage - as far as I can tell.

I noticed that. It has a little black plastic ferrule that's tightly fit onto the tip.

I appreciate the help! Phil

Phil_gretz

Stripped the frame last night. Boy was it heavy to lift onto the bike stand. The steel kickstand and clamp must weigh 2 lbs. That has to be replaced with an alloy one from the parts bin.

I re-adjusted the crankset - works fine now. I'll repack the headset tonight.

The derailleur is Positron II, and not in bad condition at all. Ultrasonically cleaned it.

The chain is quite salvageable, cleaned it with ultrasonic/degreaser, then WD-40 and brush, and now it's soaking in mineral spirits.

I bought the shifter/cable combination from an eBay seller last night. I hope that this re-installation doesn't turn out to be a nightmare. I can see where the detent/clicks are on the rear derailleur, and will replace the cable just as I removed the other one. There's a little crimp "flag" tab that goes onto the derailleur termination of the inner cable at the binder bolt. That's what really locks the cable into place. There's also a clamp ring that holds the housing to the derailleur receptacle flange. Looks straightforward.

Start with the 3rd gear position, dial it in. Fingers crossed...

I hope that I don't lose money on this bike - just breaking even (or +$50) at this point would be fine.

Thanks for the collective wisdom of the group, though. Gave me the confidence to go forward and not pitch the thing. PG

Phil_gretz

Thanks for all of your suggestions, group. Here are four photos of the final product. I put $65 into it (not counting aluminum kickstand from the old parts bin, and discarded new cable housings from the housing bin), and sold it for $125 within 24 hours of listing it. Positron II. It rode pretty well, comfortable and stable, even if heavy as heck. I bought the shifters and cables as a single unit on eBay.



Phil

Phil_gretz

And a second one, given to me by a coworker. This one had solid-to-no grease in any of the bearings, but the condition was pretty good. Similar ISO590 steel wheels. Crazy steel hubs. I couldn't bear to leave the blue vinyl saddle on it, though. Sold today for $130. Good riddance to both of them!

Of some interest, though, this one had a Positron version WITH A RETURN SPRING, which assisted in upshifting. It was still clumsy, but worked. The pulleys were blue plastic. Pretty cool. PG

esportzman

I have 1980;s world tour schwinn 10 speed...cable piano wire broke...

Now I am unable to properly set tension on the my Positron II derailleur ...
chain slips when pedaling.

Any advice would help and be most appreciated

cheers and thank you

BTW: Great looking bike.

dedhed

You either shop ebay and pay the price or try a small engine dealer for something you can modify to work.

Or you replace the derailleur and shifter with a non positron set up.

https://www.ebay.com/itm/SCHWINN-SHI...oAAOSw5EpcLEIq

https://www.homedepot.com/p/Engine-S...E&gclsrc=aw.ds

le mans

Nice pick up

I picked up a Ladies Indi 500 with the same drive train, test riding it i thought it was a positive system, just slipped in those gears..didn't mess about
so i dismantled it to fit on a mens frame. palmed the Indi off with friction shifters

Trouble is the cable's too short when i wanted to fit it to another bike

fietsbob

It's a steel solid wire, not a cable , so it can push & pull, Cables only pull, a return spring pulls it back.

freewheel in the crankset not the hub on those..

[random thought: ]
Efneo GTRO is a internally geared 3 speed crank set.. it could make an interesting upgrade

as it too has a freewheel mech within it .







...

MNebiker

Back in the 80s my wife and I had a pair of Schwinn World Tourist bikes - 10 spd with FF system and Lark friction derailleurs. We rode them until we sold off a bunch of stuff when we moved in 2003.

A couple of years ago I picked up a mint his/hers set of 1980s 10 spd World Tourists. I tore them down completely, cleaned, lubed, new tires, tubes, cables, brakes, etc. The men's had the friction system but the women's was a Positron. I had heard they were tough to adjust correctly, but it actually went real easy. I rode the men's for a bit but it was heavier riding than I remembered - maybe it was because we moved from flat land to hilly country! I sold both bikes and bought a modern 24 spd lightweight hybrid that I love. Those old Schwinns were great in their day, but can't compare to the new stuff. But I really liked the FF system - it was easier to downshift when slowing down.

le mans

Yep Positron, i just call it a cable due to the housing, at first look i thought it was a stainless steel wire

BTW not all them had the freewheel crank, on the ladies Indi 500 it had the freewheel at the rear {hub**

blinski

Hi all, I'm new here and I'm searching for particular answer when it comes to Positron system. I'm restoring Kettler Alu-Rad bike from 1983, and wanted everything to look shiny and new but also wanted to keep the original Positron II derailleur. Wire housing is in pretty bad condition: dirty, yellowed and scratched, so I wanted to replace it with new one (just like the brake cables). I demounted the wire but it seems nothing can make the housing terminations to come off. Is there some secret way to make them to, does anybody know? I wanted to change the color of housing to grey, there is no grey housing dedicated for Positron derailleurs of particular lenght (72") on ebay, unfortunately, shipping to Poland where I live would also make it not very cost-effective. Help would be really appreciated.
BTW, Happy Easter to everybody!

Nubra 

Thanks JD! This link still works for eBay and I found a Positron Housing that I needed for and old Huffy (yes, I am refurbishing an old Yellow + rust huffy) using it. My boolean search to find it on ebay didn't work, but this paricular link took me right where I needed to go.