How do I adjust my 7-speed Shimano SIS indexed shifter not to miss out one of the cogs? I have a 7-speed indexed twist-grip gear-shifter, but it was set up incorrectly: it has eight positions, the fourth is where the numbers start showing, and while it hits the top and bottom gears, it has an 'empty' click that takes it from top gear to top gear and it skips from ring 3 to ring 5 with just one click.

I've read the response to How can I adjust index shifter so it doesn&#39;t skip the second chainring? but this is a 7 speed shifter (masquerading as an 8 speed and a 6 speed), not a 3 speed, so I don't believe the answer there applies here.

It seems that the twister is giving too much cable for each click (like a 6 speed shifter) and has its own position limiters which allow extra travel (like an 8 speed shifter). I've fiddled with the top and bottom limit screws on the derailleur, and with the [barrel] that simultaneously changes where ALL the indexes locate, but while I can get it somewhat aligned for all sprockets, it still does the 'not quite engaging properly' thing for a few of them, and I still have extra clicks at top and bottom.

How do I reduce the amount of cable each click gives? There's an intriguingly yellow 'c-deck plus' sticker on the twist-grip that looks like it's hiding a screw, and a couple of tiny Allen key looking things that I'm guessing are holding the unit together.



Update: the shifter declares itself to be a 7-speed shifter on the front, and the part number bit towards the back reads 'Shimano SL-RS43-7 Singapore 22.2' which mentions '7' so... presumably it's a 7-speed.

I don't know where to find the serial number of the rear cogset..?
The Park Tool web site is generally the first place to go for info on how to do different bike repairs/adjustments.

But adjusting a derailer is fairly simple if you understand the basic principles.

First, you sorta ignore the shifter lever/handle and observe the derailer.  On it are two "limit adjustments" -- a "low" and a "high".  These are generally setscrews of a sort.  One limits how far derailer can sift in the direction that the spring pulls it, while the other limits how far the cable can pull the derailer in the opposite direction.

You first need to get the cable slack (twist the cable "barrel adjuster" a bit if needed) and adjust the stop that the spring pushes against.  This stop should be adjusted so that the derailer centers the cable over (usually) the smallest cog.  Then use the shift lever/handle to get the cable tight and pull the derailer all the way in the other direction, against the other limit screw.  Adjust that screw to position the derailer over the large cog.  (You may need to adjust the shifter slightly as you make this adjustment, to keep the derailer tight against the limit screw.)

Only after adjusting the limit screws do you attempt to adjust the cable.  If you're lucky simply adjusting the "barrel adjuster" in the cable will get everything working right, but it may be necessary to loosen the cable clamp at the derailer and slide more/less cable through it, if the barrel adjuster doesn't have enough range.

Having done all this you'd generally ride it around a bit, then go back and recheck all the adjustments, fine-tuning them.