Positron-ic!

1 02 2011

In the late 70’s, Shimano introduced its first mass market attempt at indexed derailleur shifting, Positron. There were several versions of it, starting with a dual cable version, and none of them stuck around for very long. The consensus of most of the research I’ve done on it is “good riddance.”

As I’ve been fixing up more bikes to add to the ECOS bike library, I came across one with this evolutionary dead end of a gearing system (version II to be exact). It was a cute little cruiser with a quirky shifter, and in the rush to get it stripped down and painted green, I initially didn’t realize how much of an oddball I had on my hands.

The Positron shifter. Chunky but still pretty cute, eh?

The more I examined it, the stranger it got. My second clue that I wasn’t dealing with anything like I’d ever repaired before came when I saw the “cable,” which technically isn’t a cable but a thick wire. On the derailleur, there is only one limit screw, and no springs. In the shifter, there’s neither friction nor a clicking mechanism to keep it in place. I also found that the freewheel was quite stiff, so I ran a whole bunch of oil through it and let it work through while I hit the books (er, interweb)  to try to figure out how to make it all function.

The Positron II derailleur. Notice the single limit screw and the solid wire instead of cable.

Positron is different than modern derailleurs that use a spring to return the derailleur to “normal” (high gear, except on low-normal derailleurs) when tension is relaxed on the cable. There is no tension on the Positron wire, instead it works by directly pushing and pulling the derailleur back and forth. There are five notches in the derailleur, which hold it in gear instead of springing back into high when the tension is released.

The Positron derailleur from the back. Note the saw toothed indexing mechanism that clicks each gear into place. In modern systems, the indexing action is in the shifter.

And the freewheel? It’s supposed to be stiff (though this bike may now have the loosest one around). If you’ve ever had a stiff freewheel, you know how annoying it can be as it either shifts itself into higher gears as you’re slowing down or just throws off the chain. But this doesn’t seem to be an issue with the Positron because of the lack of derailleur spring.

This springlessness also changes the strategy for adjusting the gears. After making sure the frame and derailleur were properly aligned (and bending both back into shape), I set the wire “tension” by moving the derailleur into the lowest gear and pulling the shifter down as low as it would go and tightening the pinch bolt. Then, I set the limit screw, which corresponds to the highest gear. Once I quit trying to set it up like conventional gearing, the shifter worked beautifully.

ECOS bike #38, ready to roll.

When I first met this bike, it was a sad little rusty brown Venture with a misaligned frame. Now, after a whole lot of elbow grease, it has been reborn as ECOS bike #38, ready to be loaned out and ridden again by a U of A student this spring. I took her for a little test ride in the basement corridors of SUB, and it made me glow inside when two different people randomly came up to me and said “nice bike,” (I wish I had a “before” picture). And it’s such a sweet ride – both peppy and comfortably upright, it reminded me of Marjory.

I’ll worry about it, though. The chances of finding a replacement Positron part, should I ever need one, are slim to none, and it would be easier to replace the shifter, cable, derailleur and freewheel with something more common (an old SunTour friction setup would be nice) in that situation. None of the sources on the net I looked at had any love for Positron, and even though it’s working well now, it will still need to stand up to the (often surprising) rigors of an existence in a bike share program. In the meantime, I hope many people will have the chance to enjoy this authentic 70’s ride, and I hope that Positron won’t live up to its reputation.

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Critical Lass!

17 06 2010

I had a plan for last weekend. The idea was to work all day Saturday to finish planting my garden, then head to EBC in the evening for the 24 hour Repair-A-Thon (details coming up in a future post), where I’d help people fix up their bikes and then, once things had quieted down, work on doing the final repairs to the 1950’s loop-frame CCM I had been previously working on (and blogging about). This plan, if executed properly, would allow me enough time to sleep & get dressed up for the first ever Critical Lass ride on Sunday.

Critical Lass riders roll through Old Strathcona

In reality, things never really quieted down overnight at EBC, and I didn’t get out of there until 8:30 Sunday morning.  Still enough time for a nap, shower & change of clothes before heading back to EBC for the ride, right? I sure don’t recover from allnighters like I used to (hence a 3 day late blog post). Pure stokedness (Is that a word? It should be a word, a three syllable word.)  kept me lucid & chipper throughout the afternoon.

Megan tries out the newly rideable CCM.

Critical Lass was conceived by the ladies of Loop Frame Love as a sort of girls-ride-out: pretty bikes, stylish clothes, and leave the machismo at home, please.

Hot midday sun = skirt weather! Note that there are pics of Megan riding three different bikes in this post.

It was also an opportunity to meet some of the other writers whose bike blogs I’ve been following, and as it turns out a few who’ve been reading mine.

Bringing the cool into the summer heat. Shooting from the hip while riding, I failed to capture Selene's equally cool vintage bike.

The best parts of the ride were just hanging out and getting to know so many different women who were all interested in important things like bikes and cupcakes and kids and having a laugh on a gorgeous summer afternoon.

Stylin' at a stoplight.

Our first stop was to pop by bike polo to check out a special Bike Month match (though it was slow to get started so early on a Sunday afternoon).

Polo grrrlz! Megan plays in a skirt, blouse & sandals, while Micah rocks the court in more typical polo style.

Our next stop was a short, relaxed ride through tree-lined boulevards and bike paths away. We’d get coffee before finding somewhere shady to hang out some more & take pictures.

Walking our bikes across Whyte Avenue en mass. Oh, yeah, we stop traffic.

Sweet ride + cool summer outfit = made in the shade.

Bike pile near the cafe.

Note to self: construct pretty tool roll to affix under saddle so I don't feel compelled to lug around the "utility purse" on future fashion rides.

I loved how everyone brought their own unique styles but the real beauties of the day were the conversations, the supportive atmosphere and the all-round-warm-fuzzy-confidence-enhancing-goodness of being your fabulous self rolling with a group of different, but equally fabulous ladies.

Final stop - cupcakes!

Loop frames all in a row! I love the colours of these bikes, they kinda even remind me of cupcakes.

Kudos to the organizers for getting us all together for a fantastic day! I had such a wonderful time I hardly noticed the sleep deprivation (though I do blame sleep dep for nearly escalating the little incident with the dude who moved my bike in front of Fuss). When the majority of riders on the road are dudes focused on speed and performance, it’s a huge breath of fresh air to be with folks who take style over speed, and companionship over competition.

Edit:  Check out more Critical Lass photos at Loop-Frame Love and Girls and Bicycles. If anyone else has pics they’d like me to link to (or if I spelled your name wrong or you rather I hadn’t put your name up at all, etc.) let me know!