Back to the task at hand…let’s get those limit screws on your rear derailleur to the tightest setting; while still allowing for full access to all of the gears on your cassette.
First, we’ll need to eliminate some confusion. Is the problem with shifting the result of the limiting screws…or due to some indexing difficulties? The way to eliminate the possibility of the problems being due to the indexing (shifters) is to eliminate them from the equation.
Here’s how you do it. Shift onto the largest rear sprocket while pedaling. Now, quit pedaling and shift back a few clicks. This will put some slack in the cable back by the rear derailleur. You can now remove the cable housing out of the cable stop. Now you’re set to ‘run through the gears’ manually by pulling on the cable without using the shifters.
Now it’s time to adjust the limiting screw that keeps the chain from falling off the bottom of the cassette. Shift onto the largest front chain ring and the smallest rear sprocket. If the chain falls off the smallest sprocket, you’ll need to tighten (turn it clockwise) the ‘H’ limiting screw. Do this in small increments (quarter turns) until the chain behaves itself and stays on the cassette.
If you can’t get the chain onto the smallest sprocket at all, loosen (counter-clockwise) the ‘H’ screw a little bit at a time until it drops down into ‘high gear’.
Now it’s time to go after the side of the cassette nearest the spokes. This is where real damage can occur; I mean serious damage. Zombie-like damage, the likes from which real emotional torment emanates. SPOKE DAMAGE!
You’ll need to shift onto the smallest chain ring on the front and the largest sprocket on the rear. If you see that the chain is wanting to ride up over the largest sprocket on the rear, you’ll need to tighten (clockwise) the ‘L’ screw to restrict it. If you can’t get the chain onto the largest sprocket, loosen the ‘L’ screw in increments of a quarter turn at a time to ease up the restriction.
To give it a test, put the cable housing back into the cable stop and pedal your way from large to small sprockets…and back again.
The whole procedure with the limiting screws isn’t very complicated, except if you don’t even know that limiting screws exist. Then the whole rear derailleur is a total mystery since you’ll never figure out why ‘adjusting’ the gears doesn’t seem to work. No matter how much you adjust, you’ll be hard pressed to ever get the chain onto the smallest or largest sprocket.
One of the things you’ll see if you don’t know about the limiting screws is a totally limp cable and a derailleur that still refuses to drop down into high gear. Another phenomena is you cranking as hard as you can on the shifter in an attempt to get the chain onto the largest sprocket…but to no avail.
If you’re unfortunate, you will be strong enough to either break the shifter, or the cable. And that’s an ‘avail’ you’d rather not discover.
So there you have a few words on the limiting screws of the rear derailleur. I don’t know if the business of releasing the cable from the cable stop, and then shifting by pulling on the cable/cable housing in order to shift gears is very clear. I could hardly understand my own description…so good luck to you!