Adjusting gear indices

Jules said:

My MTB runs Deore rear and Acera front derailleurs. From the 2004 model
range, I believe.

The front, when on the large chainring, rubs against the chain. However
on the middle chainring it's fine, and it struggles to get down to the
smallest chainring at all. IIRC it didn't used to do this when new ;-)

Obviously no amount of adjusting the derailleur left or right can fix
both these problems - it's too far to the left on the top ring, and too
far to the right on the bottom ring.

Which leads me to believe that the indexing is a bit screwy.

But I have not been able to find any way to adjust it. Is it possible?

Is the indexing dictated by the shifter or the derailleur?

If adjustment is not possible, then how is this situation possible?
Bent cage/frame/rings perhaps?

Cable anchor point
a) at derailleur, too far from pivot point (ie: is not anchored close
to securing nut)
b) in shifter, too close to pivot point (no idea if this is possible).

Certainly a) is possible.

Are you sure the inner and outer limit stops are not the limiting
factors?

Jules said:

My MTB runs Deore rear and Acera front derailleurs. From the
2004 model range, I believe.

The front, when on the large chainring, rubs against the
chain. However on the middle chainring it's fine, and it
struggles to get down to the
smallest chainring at all. IIRC it didn't used to do this
when new ;-)

Obviously no amount of adjusting the derailleur left or right
can fix both these problems - it's too far to the left on the
top ring, and too far to the right on the bottom ring.

Which leads me to believe that the indexing is a bit screwy.

But I have not been able to find any way to adjust it. Is it
possible?

Is the indexing dictated by the shifter or the derailleur?

If adjustment is not possible, then how is this situation
possible? Bent cage/frame/rings perhaps?

Derailleurs (whether front or rear) have three adjustments:
inner travel limit, outer travel limit, and inner/outer
relativity (the fine tuning of indexing).

The relativity adjustment will be at one end of the cable
(either the handlebar or derailleur end). It will be a knob
you can turn which adjusts the effective length of the inner
cable with respect to the outer cable. Inner cables inevitably
strech over time, so this will need tightening (try 1/4 to 1/2
a turn at a time). Note how much you turn it so that you can
undo the adjustment if you need to go in the other direction
instead.

When you get that adjustment right, you can attend to the limit
screws if need be. These will be close together on the
derailleur itself, and may be marked "H" and "L" for high and
low adjustment. Each screw will contact a stop when the
derailleur is shifted in its direction, making a simple and
effective travel limiter.

I hope that makes sense.

John

John Henderson said:

When you get that adjustment right, you can attend to the limit
screws if need be. These will be close together on the
derailleur itself, and may be marked "H" and "L" for high and
low adjustment. Each screw will contact a stop when the
derailleur is shifted in its direction, making a simple and
effective travel limiter.

I hope that makes sense.

John

I think when I bought my first bike I noticed that those screws weren't
done tightened fully so I got straight on to the job with my trusty
screwdriver. For a while I couldn't work out why it was so hard to shift
into high or low gear. D'oh!

P

Quoted message said:

Cable anchor point
a) at derailleur, too far from pivot point (ie: is not anchored close
to securing nut)

Can you elaborate - I don't understand what you mean?

Quoted message said:

Are you sure the inner and outer limit stops are not the limiting
factors?

Yep, I've tried that. In any case, if I apply a bit of pressure to the
shift lever when on the top ring, it moves to where it should be and
stops rubbing.

It's not hitting the limits.

Quoted message said:

Derailleurs (whether front or rear) have three adjustments:
inner travel limit, outer travel limit, and inner/outer
relativity (the fine tuning of indexing).

Ok - so what you're saying is they do not have adjustment of the
distance "between" the indexed points?

Quoted message said:

The relativity adjustment will be at one end of the cable

.....

Quoted message said:

instead.

Yep, I've got that.

Quoted message said:

When you get that adjustment right, you can attend to the limit
screws if need be. These will be close together on the
derailleur itself, and may be marked "H" and "L" for high and
low adjustment. Each screw will contact a stop when the
derailleur is shifted in its direction, making a simple and
effective travel limiter.

As mentioned to Duncan, it's not the limits that are the problem, it's
the actual distance between the indexes.

What constitutes the "right" adjustment of the effective length of the
cable?

Jules said:

As mentioned to Duncan, it's not the limits that are the
problem, it's the actual distance between the indexes.

What constitutes the "right" adjustment of the effective
length of the cable?

The simple answer is when it changes positively and smoothly
both up and down for reasonable chain angles (front-rear
combinations). If you screw the barrel adjuster to it's limit
and still haven't gone far enough, then you'll need to adjust
the inner cable length itself where it gets physically clamped
at its end. But you would normally have got evidence (by
improvements) that you were heading in the right direction
before reaching the end of the adjustment.

From your description, it does sound like there's a limit-screw
adjustment problem somewhere, but the indexing adjustment
should be right first.

It's all a bit like the story of the bloke who objected to being
charged $50 to have a faulty component fixed by hitting it with
a hammer. He wanted an itemized account. This was delivered
as: "$0.50 for the hammer blow, and $49.50 for knowing where to
hit." Frustrating though it is, you'll need to experiment
while you get the hang of these adjustments.

Just occasionally, certain front derailleur problems can be
solved by bending the "ears" of the derailleur (the extensions
towards the front of the bike) a little - usually inwards.
These may have got out of shape in use. But I'd consider
looking at this possibility as an absolute last resort.

John

Jules said:

... if I apply a bit of pressure to the shift lever when on
the top ring, it moves to where it should be and stops
rubbing.

It's not hitting the limits.

Is this happening at the extreme where inner cable is being
pulled tight, or when it's being released?

If it's being pulled tight, the inner would need to be tighter
still. Unless it's being caused by the inner cable starting to
break up, this might mean getting extra adjustment by means of
the moving the clamping point.

If it's not releasing far enough, this is less likely to be an
adjustment issue because cables stretch in use (unless it's
already been incorrectly adjusted). What's quite possible here
is an inner cable binding inside the outer. And that can also
be caused by the inner beginning to break, strand by strand.

John

Jules said:

Quoted message said:

Cable anchor point
a) at derailleur, too far from pivot point (ie: is not anchored close
to securing nut)

Can you elaborate - I don't understand what you mean?

it's a simple lever arm.. if you connect the cable further from the
pivot point, then the derailleur will move less per mm of cable
movement.

eg: if the cable were designed to anchor on the inside of the nut, but
you put it on the outside, you would lose a significant amount of
throw.

Do shimano levers really have such limited pull?.. I thought front
dr's had heaps of cable pull and relied on the limit stops

btw, make sure you check out
http://sheldonbrown.com/derailer-adjustment.html

for all the good oil.

On 2007-05-16, John Henderson (aka Bruce)
was almost, but not quite, entirely unlike tea:

Quoted message said:

Jules said:

... if I apply a bit of pressure to the shift lever when on
the top ring, it moves to where it should be and stops
rubbing.

It's not hitting the limits.

Is this happening at the extreme where inner cable is being
pulled tight, or when it's being released?

If it's being pulled tight, the inner would need to be tighter
still. Unless it's being caused by the inner cable starting to
break up, this might mean getting extra adjustment by means of
the moving the clamping point.

If it's not releasing far enough, this is less likely to be an
adjustment issue because cables stretch in use (unless it's
already been incorrectly adjusted). What's quite possible here
is an inner cable binding inside the outer. And that can also
be caused by the inner beginning to break, strand by strand.

That or the cables being full of junk. Both problems can be diagnosed
by ripping the cable out of the outer, giving it a wipe down or
throwing it out if it is breaking apart. If it looks like the outer
is filled with [censored] (you wiped a lot of [censored] off the inner), replace
the outer cable -- they're cheap, and I've usually found them at
fault. Put a bit of dry lube down the outer if it's not too bad,
before replacing the inner.

--
TimC
"Saving four times is just paranoia. Unless you're using an Exabyte
5gig/8mm tapedrive." -- Graham Reed

"Jules" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Obviously no amount of adjusting the derailleur left or right can fix both
these problems - it's too far to the left on the top ring, and too far to
the right on the bottom ring.

If nothing else has changed then this just isn't possible and it has to be
adjustable. The only thing that might screw this up is if you've swapped out
the bottom bracket for a narrower or wider one than it was originally fitted
with (that happened to me).
Some brilliant guides at
http://www.parktool.com/repair/byregion.asp?catid=53 that have helped me a
lot sorting out shifting issues amongst other things.

--
www.ozcableguy.com
www.oztechnologies.com