After wrestling with derailleur adjustment for a couple of weeks, and still having the rd jump gears, especially when going large to small, I broke down today and took the Lemans to the LBS to see what I had done wrong. Reasons from the bike mechanic, in no particular order. 1. cable incorrectly routed 2. wheel not seated completely back in drop-out (felt really dumb on this one) 3. bent hanger 4. worn index part at the lever (he did show me a lot of play before clicks) My short term solution is friction shifting, which may also be my long term solution. They looked for parts, and could only come up with a set of replacement levers. Problem? Dura Ace at $120 the set. I really don't want to add that much onto the project at this point. Are there sources of old SIS parts out there? Or, am I destined to ride clickless?

There's several local shops that deal in good used parts. However, that's Portland for you. Checked Ebay lately?

Also, what do you mean "wheel not seated completely back in drop-out"? Do you have vertical or horizontal dropouts? If they're vertical, then you're OK, but many horizontal dropout bikes need to have the axle forward of the rear-most position.

Older SIS is not easy to find only because there is very little demand. There should be someone on ebay selling a set cheap but they need you more than you need them. Keep posting here and specify are you looking for 6 speed or 7 speed. Last time I looked, 7 speed was still in demand, but the only folks looking for 6 speed are guys, like yourself, who have a worn out unit. BTW the bent hangar alone would have caused the problem you described. After it's fully adjusted, try the SIS again, it might work fine.

Need some pictures of the rest of your setup. How's your chain?

I'm assuming this is horizontal?Evidently I didn't get the axle back against the metal piece.

The chain is new. Pic attached. The shifting did not fully improve after the hangar was straightened, and the mechanic showed me what looked like a lot of play. The unit is a six speed, so it looks like lucking onto the part is the best I can hope for. Am I right that the stops for the indexing are around a plastic sleeve inside the shift lever body?

1. A possibilty
2. As long as the wheel is centered it's marginal
3. Yes, that could do it
4. 100% B.S. That 'play' is supposed to be there, it's a key reason as to why indexed shifting works the way it does.

Without being able to see it I'm going to say the upper jockey wheel is worn out or its a cable issue.

Do you know how to properly adjust S.I.S.?

Just look on eBay- they're very common. Here's a set of light action shifters just like yours- vcheap, no bids, ends in 2 hours.
https://www.ebay.com/itm/USED-Shimano...item337e48f6f7

When you own a bike like yours, eBay is your friend.

+1 No luck required, they are for sale on ebay, pretty much continuously. I have bought many sets on ebay. I am patient, so I wait for a deal (spread of prices is pretty wide on ebay).

+1 When you own a 25 year old bike, with technology that went out about 20 years ago, the used market is your friend: donor bikes, co-op, ebay, and the marketplace on this forum are all your best sources. Bike shops do not use these sources, so not surprised they didn't have a reasonably priced alternative.

Note, I also occasionally pick some up used at bike shops. Some shops have buckets of misc parts, I have picked up three sets of bar end shifters in the last couple months this way. One set was actually NOS, still in original bag.

+1 Lots of causes that would not be the shift levers. Those levers are very durable.

Light Action shifters don't often fail, so I'd go there last.
Even then, there are both 105 and Light Action 6-sp sets out there.

I don't get his "go to DA shifters" solution. Upgrade to 10sp?
That's a lot for a shifter problem. Wheels, cassette, RD, chain...

RD hangar, wheel seated well and straight across, check the cable clamp point on the RD.
Also check the cable routing under the BB, it could be hung up or have missed one of the channels....

I've got a set, but they're in use. I'd go 7-sp SunRace if I could find a 7-sp freewheel....

Darn- I missed that. I agree: the older SIS shift levers had built-in play to allow a slight over-shift. I guess Shimano took that away when they moved to more gears. Note that you should not use Dura-Ace shifters on your bike- Dura-Ace of that era was incompatible with everything else Shimano made. It wasn't until 9-speed came along that Dura-Ace was cross-compatible with other Shimano group.

+1 about using D-A shifter or derailer with non-D-A derailer or shifter, respectively. Doesn't work.

If you remove the shifter from the frame, there is typically a tiny hole drilled in the back side that has a peg partly filling it. Add several drops of light lubricant like Tri-Flow to be sure the indexing isn't fouled with corrosion. The click action should be very crisp, and free-play is normal.
Don't use WD40, it's too thinned with kerosene to offer good lubrication.

The cable wire needs to positively be seated in the groove in the derailer's actuator arm (where the anchor bolt pinches the wire). Accurate indexing depends on this.

Also tug on the exposed cable wire along the down-tube, to check for smooth take-up and return of the derailer movement. Should be really smooth if the rear cabling is in good order and the guide is lubricated.

I kind of doubt that any parts are bad here, cept for maybe the cable.