Index to Non-Index Shifting
 

My 31 year old Suntour 7-speed index shifting derailleur seems to be auto converting to fiction shifting.
Before I frighten it by threatening to "fix" it I thought I would consult the collective genius of the Forum for advice.
Ignore it, tighten this, lube that, buy a new bike?
Thanks in advance.

Hard to see how the derailleur could be at fault. Are you sure it's not the shifter?

Almost certainly the shifter. May be worn out, or maybe just needs a clean and lube.

The Suntour Accushift index system usually has the 'clicks' on the shifter, not the RD side. The RD just moves into the proper position by the correct amount of cable pull. The RD should just move smoothly, no detents on that end.

You could disconnect the cable at the RD and check that the shifter 'clicking' properly.

Thanks.
I have visions of small, obscure parts flying off into the wild blue yonder upon disassembly.

A little more info about what is happening would be helpful.

Also, the setup that you are using. Downtube shifter?, MTB shifter? Model #?, RD? Freewheel type? Cable & housing type & condition?

There are a few people on here that are familiar with Accushift in certain configurations and may be able to help you if more detail is provided.

As has been pointed out repeatedly in this thread, the problem is almost certainly not in the shifter. Couldn't hurt to drip some lubricant into the shifter without disassembling it, though. In any event, don't disassemble it.

Far more likely: the cable housing may be kinked or whatever lubrication it might have had at one time may have evaporated. The inner wire may be kinked.

Good call, especially for Suntour shifters of that era.

Pratt, do a search for information on your shifter model (the model number should be visible). You'll likely be able to find instructions on how to switch the (right-side) shifter between indexing and friction.

Some models can be switched to a "soft" click setting---the lever ratchets, but the detents do not correspond to indexing positions.

Actually the consensus seems to be that it probably is the shifter.
That's reasonable advice. My success rate reassembling shifters is less than 100%.This is quite likely the case.

Usually.

The derailleur moves the chain sideways. The cable pulls the derailleur cage. The shift lever pulls the cable. It either has clicks that determine how much cable gets pulled, or the user does that. It's usually the case that when a rear derailleur no longer indexes properly that something whacked it and bent it, or the hanger.