xroadcharlie

How do you align the rear derailleur using the barrel adjusters once it has been properly installed and otherwise adjusted.

I tried eyeballing the jockey wheels with the sprockets in different gears stopped. When it jumps between gears, I stop and make more adjustments. I haven't had much luck with that and thought it might be a stretched chain. This morning I got really frustrated with the jumping between gears so I turned the barrel adjuster at the shifter and tested the shifting on the fly. Knock on wood it seems to be much better now.

I'm just curious to know if there is a standard procedure the bike shops use to do this.

cxwrench

Yes, there is. There are tons of good videos on YT that show how to do it. Try Park Tools or Art's Cyclery.

xroadcharlie

Thanks, I'll check some video's.

Mr. 66

The barrel only adjusts cable tension, alignment should be done at the hanger. Are your parts all matching pull ratios to parts?

70sSanO

The first principle is to understand that an index system has a starting point and every shift references from that starting point.

For standard top normal rear derailleurs that starting point is the 1st position cog.

In theory, if that is aligned correctly, the barrel adjuster should only be needed to ensure that the cable is taut, and any slack is taken out.

In reality, for me, I fine tune the setup in a middle cog by turning the barrel adjuster one direction till the chain starts to clatter then back the other direction to the same point and then set it at the middle point; or slightly shade it one way.

John

xroadcharlie

The bike is mostly stock and 2018. I had the Shimano Tourney derailleur replaced with an Altus at the bike shop after clumsy me stepped on it. Im pretty sure it has the correct parts.

I didn't know the Barrel adjuster at the shifter was for cable tension. Very good to know, thank you. I assumed it was for alignment since the rear derailleur is moving a small amount when I turn it a lot. It makes sense now. Perhaps the cable moves a little differently with changes to the tensioner allowing for minor alignment adjustments.

dedhed

It doesn't really adjust "tension", it adjusts cable effective length, like chain "stretch" is really pin & roller "wear". That's why you see the derailleur move. The upper pulley on a Shimano index derailleur has side to side float to allow for minor misadjustment to not affect shifting. The pulley moves slightly to match the cog. Proper hanger alignment is also important. "Stepped on" could cause this, although I'd like to think the shop checked/adjusted when installing a new RD.

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cxwrench

Ok, this is as good a time as any to explain how this really works.

The barrel adjuster(s) do NOT adjust cable tension, that is always the same. You're changing the length of the cable relative to the length of the housing. Adjusting this will move the derailleur one way or another. The rate of the derailleur spring is not changed so you are not changing tension. BOTH barrel adjusters do the exact same thing so it doesn't matter whether you adjust at the shifter (if possible) or the derailleur (if possible). It is fairly common to refer to this adjustment as 'tightening' or 'loosening' the derailleur but that is not actually what happens.

All shifts move the same amount so if you have problems in certain gears you either have an out of alignment hanger and/or wear issues in those cogs.

70sSanO

Whether it is called tension or effective length is moot.

When you use the barrel adjuster it is called effective length, but turning a spoke nipple is changing the tension, even though it is really changing the effective length.

John

dedhed

Changing the length doesn't change tension on a RD. OK, maybe a minuscule amount depending on where you are in the range of the RD and working against the spring or when against the low stop. Because a spoke is fixed on both ends you are changing the tension.

It's really not moot IMHO in that people should understand the concept of how it really does what it does. It's not the magical "I got the tension right" but "I've got the location right with respect to the cogs and the shifters".
I get it, BF is full of cable tension, chain stretch, and other misnomers, but understanding what really goes on would sometimes speed people along the process of resolving their issue.

squirtdad

I think OP is really talking about setting up indexing this is my go to

70sSanO

Actually shift cable tension changes with every shift. Easy test is to pluck the shifter cable, you can use a pick if you prefer, like plucking a spoke and the pitch changes.

How can that be if tension never changes?

John

smd4

In fact, some books from back in the day refer to the cable adjuster as a “cable length adjuster.”

cxwrench

No, it doesn't. If the amount of force needed to move the derailleur changes it's drag in the cable/housing NOT a rise in spring rate. The tension never changes because the spring rate never changes. It's a LINEAR rate spring. Every time you shift it should feel the same, if it doesn't there is some other problem. Take the chain off and push the derailleur body towards the large cog, it will take the same amount of force to move across it's range of travel.

70sSanO

I don’t have any problems, but I do my own tune-ups. I like drop D for my granny gear as it gives me more power on climbs, which strikes a chord with me. I don’t stay in it for a lot of miles as it can cause metal fatigue. But always a welcome genre from time to time.

John