Bicycle Mechanics - tune-ups

in the past, when my gears started skipping, that would tell me it was time for a tune-up. I'd like to know how to perform this repair myself.
I know that the rear derailler is not bent. when skipping occurs, the gear does not change. I do not know if the skipping occurs on the rear cogs or the front rings. I can't tell when I'm riding. it only happens under load, like when I'm pedaling hard, but it is getting worse. I cannot get it to skip by rotating the crank by hand.
is this a matter of adjusting the limit stop screws, or the adjusting barrel at the end of the cable housing, or what? is it more likely to happen in the front or rear? I can't tell.
keep in mind that this is the same problem that I always have every few months or so. any advice would be greatly appreciated. thanks.

It sounds like your chain is worn, possibly your cogs too.
Chains actually stretch. Then they will skip just as you are describing. When the cogs wear, the teeth start to get a curved look to them.

The stop screws are the inner and outer limits of how far the derailler can travel, if your chain is not falling off of either side of the cogs, don't touch them. The barrel adjuster adjusts the derailler to be inline with the cog. This being out of adjustment usually shows up as unexpected gear changes or the gears not quite changing when you shift.

It sounds like it is time for a new chain, at least.

It's the barrel adjuster. The cable slowly stretches. The barrel adjuster accounts for the stretch. If it doesn't happen when turning the cranks by hand, turn the barrel adjuster out in quarter turn increments and take it for a ride until it stops.

Usually you can get it to do it by hand though by turning the cranks and constantly shifting up and down. You want to get it to the point where you just shifted to a larger cog but the chain hasn't gone yet. You can then turn the barrel adjuster until it shifts and you are done.

-s

I think Avalanche325 is correct. If the problem was due to cable stretch or derailleur adjustment, the problem would present itself regardless of whether the drivetrain was under load or not. Since the problem is not with shifting between cogs, it's likely a worn chain.

interesting. we've got two possibilities here. maybe it's just that I don't want to have to replace my chain or cogs, but I tend to believe Slider. this is a problem that has happened to me many times in the past, and has been corrected by a professional tune-up.

Well try the cheap option first. Clean the chain and derailleurs and adjust as described. If it works you're golden, if not look to worn out parts. Depending on how many miles you have on the bike you might want to look into chain stretch just to be safe and save yourself some money. I let mine go too far too often and waste cogsets.

-s

ok. I'll try it. the one thing I don't understand is this: you shift down, but before the chain goes, you're supposed to adjust the barrel until the chain switches cogs on its own, right? so the chain switches without turning the crank? I didn't think that was possible. also, turning the barrel adjuster counter-clockwise tightens the cable, right? again, thanks for any help anyone may have.

Turning the barrel adjuster out (counter clockwise) lengthens the distance of the cable housing, which has the inverse result of shortening the effective length of the cable. Make sense? Yep, it's kinda confusing.

Think of it this way. The cable length is fixed at one end with the shifter and the other by the derailleur. The barrell adjuster changes the length of the housing. Thereby lengthing it. If the housing gets longer and the cable length is constant, the cable tension increases.

O.k., now that I've confused you.

Shift into you smallest cog in the back, then shift up one gear. While pedaling turn the barrell adjuster out (CCW) until it starts "climbing" into the third gear. Then turn the barrell adjuster back in until it's smooth again. This centers the derailleur between the clicks on the shifter. If you look at the cog from the rear of the bike, the upper jockey pulley should be directly below (in line) with the 2nd cog. Shift through all your gears to make sure it shifts well. If slow on the upshift (to bigger cogs) turn barrell adjuster out (CCW) if slow on the downshift (to smaller cogs) turn the BA in (CW). Play around until you have a compromise between the two.

However, I think your problem is in fact a worn chain or cassette or both. To further clarify (or confuse) a chain doesn't stretch. The plates where the pins connect wear and the distance between pins elongates. There is a tool that is used to measure the distance and indicates when a chain is "stretched". If a chain is "stretched" (worn) too much, it will also wear out the teeth on your cassette.

I usually change my chain about 3 times as often as my cassette. IOW, I change my cassette every third chain.

Good Luck,
Sorry so confusing, but I'm amped on Mt. Dew's. AND it's late!

L8R

If the problem was due to cable stretch or derailleur adjustment, the problem would present itself regardless of whether the drivetrain was under load or not.

Actually, SteveE, when you are experiencing chain elongation, the chain will usually skip only under load.

Actually, SteveE, when you are experiencing chain elongation, the chain will usually skip only under load.Correct. I was trying to point out that if it was due to shifter cable stretch or poor derailleur adjustment (resulting in slipping from a larger cog to a smaller one) then this would occur in both unloaded and unloaded conditions. If the drivetrain is slipping due to chain elongation, it will will generally occur only under load and the chain will not shift between cogs but merely slip over teeth on the same cog.

this would occur in both loaded and unloaded conditions.

I find that when things are out of adjustment and/or gunked up, shifting problems present themselves first under load. If things are gunked up, I'll start to have problems grabbing the granny on steep hills or dropping to smaller cogs under load.

If it's just cable stretch it'll be slow to shift up to larger cogs/rings under load. Take a close look at the HG ramps on the cogset and think about what happens to a chain under load and this makes sense. An unloaded chain "rides up the ramps" easier than a loaded chain which has a tendency to slip off when slightly out of adjustment. An older more flexible chain can aggravate this long before "chain stretch" starts damaging the cogset.

I'd definitely try tuning it up before I spent money on parts.

-s

Clean and lube everything, then try adjusting it out.

The advice on changing the chain at a regular interval is extemely helpful. Preventive maintenance is always cheaper in the long run.

It could be a combination of a worn chain/cassette and also your derailer might be out of adjustment. If the barrel adjuster won't fix the problem, shift your rear derailer to the smallest cog on your cassette. If you can see or feel if the cable is loose then you will have to unscrew the anchor bolt/screw that holds the cable, pull the cable out until there is no slack in it, then retighten the anchor screw. After all that you should then use the barrel adjuster to fine tune the adjustment, it should be as good as new after that as long as your cassette and chain are not worn.