Bicycle Mechanics - When To Adjust Indexing Screw?

First of all, I am a newbie. I have never accurately adjusted a derailer. Everything that I have read about adjusting a rear derailer talks about the chain not traveling from the outermost rear cog to the second outermost cog properly.

What if it is the intermdiate cogs that seem to have trouble? My bike shifts fine but when it is on the largest front chainwheel and on intermediate cogs it seems more sluggish. I have a 24 spd. When I shift to gear 4 or 5 on the rear it seems sluggish. By sluggish I mean that sometimes I have to hit the thumb shift an extra time to get it to go. Now that I mention it I think it seems always to be the thumb side which would be shifting to a larger or more innermost rear cog.

Why would it just show up when it is on the largest front chainwheel?

Could be cable tension. Try turning a cable barrel adjuster (located either where the cable enters the shifter mechanism, along the cable housing where it is attached to the frame or where the cable enters the rear D'rer) 1/4 turn counter clockwise (the general guide is to turn the top of the barrel adjuster the direction the chain is having difficulty traveling along the cogs) and recheck shifting action. Keep doing this until shifting gets better. If it never gets better then check the cable housings, especially the noodle (the cable housing between the frame and the rear D'rer) for smooth cable movement. I spray my cables with teflon chain lube and wipe them dry in the areas where they are inside the housings. If you can't get smooth stiction free cable movement, replace the cable and housings.

Index screws are used to adjust the distance the D'rer can travel. Use your shifter to put the chain on the smallest cog, then with the rear wheel off the ground, pedal with one hand and use the other to push the D'rer all the way up onto the largest cog, then let it fall freely onto the smallest cog. If the chain has full range and doesn't go off the cogs in either direction your index screws are set correctly.

Hope this helps,

T/E

Advice noted. I will try. Is this adjustment not linear? Why do most gears work fine but the 3 (front)/4-5 combo seems sluggish in shifting?

The fix may be more subtle. Try easing up on your pedaling stroke when you shift.

.......also, your drivetrain simply may need some good cleaning & lubing. May not even be an adjustment problem.

There are many variables that can cause this. One is old cables and housing. It never hurts to replace these after a while. Two is worn rear cogs and a worn chain. Three is like mentioned cable tension. Four is the housing could be too long. Five is a bent derailleur hanger. Six is the wheel may not be seated properly. Seven could be a worn out shifter. The easier fixes is try adjustments for they are free. A good reference for this can be found here: http://www.parktool.com/repair_help/FAQindex.shtml

Advice noted. I will try. Is this adjustment not linear? Why do most gears work fine but the 3 (front)/4-5 combo seems sluggish in shifting?

I have not examined this in any detail, but I think that the position of the jockey wheel (the upper cogged wheel of the rear derailleur) -- how far it is from the cogs -- is one of the variables that would cause some gears to have problems but not others. This would be affected by which chainring you are on.

This is just a theory I have.

When I had a problem on a recent tour, I just adjusted the cable tension u.til it went away. (not very scientific).

I have had this problem if the chain is to short or to dry.

My 24 speed does the same thing, I blame it on age and wear (15 years old, about 2000 miles). My cassette, chain and chain rings are shot. But, they still make the bike go.

I fiddled with everything many times over and have just learned to push the lever twice if it does not jump up to the ring. Keeping everthing clean and lubed helps (I cleaned out the shifters and lubed those as well)

I know this does not help much, but you are not alone.

ehenz

My 24 speed does the same thing, I blame it on age and wear (15 years old, about 2000 miles). My cassette, chain and chain rings are shot. But, they still make the bike go.

I fiddled with everything many times over and have just learned to push the lever twice if it does not jump up to the ring. Keeping everthing clean and lubed helps (I cleaned out the shifters and lubed those as well)

I know this does not help much, but you are not alone.

ehenz

Can't blame mine on age or probably even wear. My bike is 2 months old and probably has 700 miles on it. (approx) LBS said it shifts fine and it does on the stand. Just under load it does the aforementioned. It really isn't that big of a deal. I can live with it too. I was just wondering if there was a fix. I am not going to mess with adjusting it unless it gets worse.