CrankyFranky

I normally ride friction shifters on old steel for shorter rides. I purchased a nice ’86 Tange#1 complete bike (in VG original condition) recently so I could have an alternate commuter when the other one needs wrenching. This ’86 has Shimano 600 SIS. I’m completely unfamiliar with these early indexers and how they operate and adjust. I’m not much of a masher due to bad knees, but currently, the right shift lever allows the 6208 RD to pop out of the lower gears upon putting pressure on the pedals. The housing and cable are in very good condition and appear original, like everything else on the bike. The chain appears to not be stretched and the freewheel seems OK too. I removed the SIS lever and it looks as if there is not a lot of wear. The jumping is most prominent on the lowest gear of the six speed SIS freewheel. I found a instruction “SIS Adjustment Procedure From: Bob Fishell” on the web, and I had a go using that procedure. Maybe I have to keep at it a few more tries. The friction mode doesn't seem to hold either. Does anyone have any helpful advice or links? Thanks in advance!

Bill Kapaun

The shifter wouldn't have any preference as to applying power to the pedals or not.
It would slip all the time.

Sounds more like worn chain/cogs.

FBinNY 

If it pops out ONLY in the lowest gear, I suspect that the limit is set a bit conservatively and not allowing the lever to click in fully. So it's hanging only partly engaged and it doesn't take much to pop it out.

This is easy to check by shifting into low and gently tugging on the cable to feel how much holding power the lever has. Then try the next gear where the limit isn't a factor and see if it's the same. If the low hold is significantly weaker then back the limit off as far as possible, while still bulletproof ensuring that the chain cannot overshift and see if it resolves.

It's also possible that the lever is worn, and the escapement mechanism isn't holding solidly. Sometimes, this isn't wear but dirt and dried grease, so sprat some solvent/light lube into the lever, and work it back and forth through the range a number of times, and see if it improves (does about half the time). If so, clean off the excess solvent, lube with a very light oil, and you should be fine.

Andrew R Stewart 

Some of the early gen DT levers had an easily broken "star" washer in the mechanism. If this "star washer" is broken and/or missing the amount of over shift and return to on center movement the lever goes through increases. If this happens then it's easy to end up adjusting the cable for a lever position that's not the true center position. Bumps, stress and frame flex will draw the lever from the thought was right position to the actually is right one, and the der pulley will now not be centered under the cog.

These levers can usually be set to a friction mode. If so how does the system work in friction? Andy

CrankyFranky

Thanks for the info guys - my impression is that it mainly doesn't hold in the lowest gear (ditto with friction mode), so I'll definitely futz with the lower limit. I'm not sure frame flex is a primary influence but will watch that too - simply haven't rode it more than 5 miles. I'm within the weight limit for Tange#1. I had cleaned the shmutz out of it inside and out, so now when I view with a magnifying lens, it looks pretty clean. The copper star washer is intact. I was thinking that there might be a part missing.

Will report back later tomorrow. Cheers!

CrankyFranky

So... the answer is... lower limit screw. Looked as if it was perfectly aligned but as FB in NY said, needed a bit of tweaking. Works fine in SIS now. But in friction, not so much - still won't hold, and can't tighten it by counterclockwise movement on the adjuster ring-thing. But no matter, SIS will do. Thanks again!