Stronger return spring for front der?

[Dave]

I have a full sus MTB whose design makes for some difficult front
shifting under pressure. Their prescribed fix is to use a DA triple FD
because of the stronger return spring. I currently have an XT FD, and
since the spring can be accessed by removing the circlips I'm wondering
whether it would be possible to buy a stiffer spring and install it in
my existing derailleur. Anyone know of a source?

Alternatively, is there some other hackish method of raising the spring
tension?

 

[[email protected]]

On 15 Jan 2007 11:48:41 -0800, "Dave" <[email protected]> wrote:

>I have a full sus MTB whose design makes for some difficult front
>shifting under pressure. Their prescribed fix is to use a DA triple FD
>because of the stronger return spring. I currently have an XT FD, and
>since the spring can be accessed by removing the circlips I'm wondering
>whether it would be possible to buy a stiffer spring and install it in
>my existing derailleur. Anyone know of a source?
>
>Alternatively, is there some other hackish method of raising the spring
>tension?

Dear Dave,

Very hackish--shorten chain a link?

Cheers,

Carl Fogel

 

[dvt]

[email protected] wrote:
> On 15 Jan 2007 11:48:41 -0800, "Dave" <[email protected]> wrote:
>
>> I have a full sus MTB whose design makes for some difficult front
>> shifting under pressure. Their prescribed fix is to use a DA triple FD
>> because of the stronger return spring. I currently have an XT FD, and
>> since the spring can be accessed by removing the circlips I'm wondering
>> whether it would be possible to buy a stiffer spring and install it in
>> my existing derailleur. Anyone know of a source?
>>
>> Alternatively, is there some other hackish method of raising the spring
>> tension?
>
> Dear Dave,
>
> Very hackish--shorten chain a link?
>
> Cheers,
>
> Carl Fogel

I suspect you are thinking of the rear derailer. I don't see how
shortening the chain will help the front derailer (FD) return spring.

--
Dave
dvt at psu dot edu

Everyone confesses that exertion which brings out all the powers of body
and mind is the best thing for us; but most people do all they can to
get rid of it, and as a general rule nobody does much more than
circumstances drive them to do. -Harriet Beecher Stowe, abolitionist and
novelist (1811-1896)

 

[[email protected]]

On Mon, 15 Jan 2007 19:38:42 -0500, dvt <[email protected]> wrote:

>[email protected] wrote:
>> On 15 Jan 2007 11:48:41 -0800, "Dave" <[email protected]> wrote:
>>
>>> I have a full sus MTB whose design makes for some difficult front
>>> shifting under pressure. Their prescribed fix is to use a DA triple FD
>>> because of the stronger return spring. I currently have an XT FD, and
>>> since the spring can be accessed by removing the circlips I'm wondering
>>> whether it would be possible to buy a stiffer spring and install it in
>>> my existing derailleur. Anyone know of a source?
>>>
>>> Alternatively, is there some other hackish method of raising the spring
>>> tension?
>>
>> Dear Dave,
>>
>> Very hackish--shorten chain a link?
>>
>> Cheers,
>>
>> Carl Fogel
>
>I suspect you are thinking of the rear derailer. I don't see how
>shortening the chain will help the front derailer (FD) return spring.

Dear Dave,

I see what you mean, but no, the idea is that a slightly tighter chain
paradoxically pulls down and in more easily off the front sprocket.

I don't know why.

It could be that the tighter chain gives a slightly better angle for
the lower run to come off the front sprocket by pushing the rear
derailleur down a little farther.

That is, there's slightly less chain wrapped around the front sprocket
when the rear derailleur arm is pulled down further by a tighter
chain, so the chain is less inclined to stay wrapped around the front
sprocket.

But that seems like a small angle change to me.

Or it could be that the greater chain tension helps to pull the chain
off the front of the front sprocket as the about-to-shift section of
chain rotates downward.

But that also seems unlikely. A tighter chain ought to fight to keep
itself on the sprocket, shouldn't it?

Whatever the cause, I've seen some reluctant front-shift problems that
vanished when a link was removed. Chain wear, sprocket wear, or just a
bad front derailleur installation could also have confused things.

I suspect that it's a try-it-and-see situation, where some setups will
improve, others will be unchanged, and some will actually be made
worse by shortening the chain a link.

The real cure would probably be a stronger front derailleur spring to
give the chain a firm shove off the front sprocket, but a lot of goofy
shift problems change with chain tension.

Cheers,

Carl Fogel

 

[Phil, Non-Squid]

Dave wrote:
> I have a full sus MTB whose design makes for some difficult front
> shifting under pressure. Their prescribed fix is to use a DA triple
> FD because of the stronger return spring. I currently have an XT FD,
> and since the spring can be accessed by removing the circlips I'm
> wondering whether it would be possible to buy a stiffer spring and
> install it in my existing derailleur. Anyone know of a source?
>
> Alternatively, is there some other hackish method of raising the
> spring tension?

Re-compressing the spring is going to be difficult with something that
small. Usually the derailleur, unless corroded, isn't the cause of the
problem.

When you said "their prescribed fix," who is "they?" Your LBS? I would
look for a second opinion.

--
Phil

 

[Werehatrack]

On 15 Jan 2007 11:48:41 -0800, "Dave" <[email protected]> may have
said:

>I have a full sus MTB whose design makes for some difficult front
>shifting under pressure.

Presumably this is due to their having included too many sharp bends
in the cable path, a not-uncommon error.

>Their prescribed fix is to use a DA triple FD
>because of the stronger return spring. I currently have an XT FD, and
>since the spring can be accessed by removing the circlips I'm wondering
>whether it would be possible to buy a stiffer spring and install it in
>my existing derailleur. Anyone know of a source?

You would have to make it yourself. I doubt that this would prove
feasible.

>Alternatively, is there some other hackish method of raising the spring
>tension?

If the cable includes a routing section where there is a gap between
segments of the housing, it might be possible to add a screw-clamped
stop and a second spring of some sort, but I think this is really not
the right fix. I'd start by getting a mandrel-drawn stainless cable,
and some really good lined der housing, and building a new cable,
rerouting it or optimizing the path (if feasible) to reduce the
severity of the bends. IME, a slippery cable and a proper path
(including an adequately large loop at the der end) usually makes just
about any reasonable cable routing reliable. Much of the time, just
increasing the length of the der cable housing at the rear, so that
the radius of that last curve is larger, will make enough of a
difference to make things tolerable...but a smooth, mandrel-drawn
cable helps a lot as well.

--
My email address is antispammed; pull WEEDS if replying via e-mail.
Typoes are not a bug, they're a feature.
Words processed in a facility that contains nuts.

 

[Dave]

Phil, Non-Squid wrote:
> When you said "their prescribed fix," who is "they?" Your LBS? I would
> look for a second opinion.
>
> --
> Phil

Its a Klein Palomino, using a design licensed from Maverick. The poor
front shifting is a known drawback of their "monolink" design, probably
aggravated by Klein's implementation of it - I believe it is because
the angle of the front der changes in relation to the chain as the
shock compresses. They recommend DA triple FD's specifically because
of the strong return spring.

My problem, FWIW, is difficulty shifting from the middle to the small
chainring under pressure. I shift, the FD releases and starts pushing
the chain, yet the FD is unable to disengage the chain. If I continue
pedaling a few more revs, I get chainsuck rather than a shift

The FD is an XT and the crank is a Truvativ Firex Team.

 

[Dave]

Phil, Non-Squid wrote:
> When you said "their prescribed fix," who is "they?" Your LBS? I would
> look for a second opinion.
>
> --
> Phil

I neglected to mention that "they" is Maverick

 

[Dave]

Werehatrack wrote:
> Presumably this is due to their having included too many sharp bends
> in the cable path, a not-uncommon error.


The cable routing is indeed circuitous, but the shifting problems occur
only when going from middle to small ring under pressure. On level
ground and on the stand, the shifting is perfect. Would you still
suspect cable drag?

 

[Qui si parla Campagnolo]

Dave wrote:
> Werehatrack wrote:
> > Presumably this is due to their having included too many sharp bends
> > in the cable path, a not-uncommon error.
>
>
> The cable routing is indeed circuitous, but the shifting problems occur
> only when going from middle to small ring under pressure. On level
> ground and on the stand, the shifting is perfect. Would you still
> suspect cable drag?

I suspect chainline and how far inward the FD is traveling...since in
the stand it's OK, but when lots of tension on the top part of the
chain, it's reluctant to come off.
Also may be FD alignment and/or height, making sure the 'bump' on FD is
against the chain when you shift. If the seatube angle is shallow, it
may not work well. May try to bend the 'nose' of the FD in a wee bit
also. FD outside cage should be aligned with the chain when in big ring
and small cog...that also 'encouregs' the FD to move the chain to
smaller cogs..

If you have a 2 piece crank, yer pretty much SOL. BTW-A DA FD is not
compatible with shimano MTB shifters.

 

[Qui si parla Campagnolo]

Dave wrote:
> Werehatrack wrote:
> > Presumably this is due to their having included too many sharp bends
> > in the cable path, a not-uncommon error.
>
>
> The cable routing is indeed circuitous, but the shifting problems occur
> only when going from middle to small ring under pressure. On level
> ground and on the stand, the shifting is perfect. Would you still
> suspect cable drag?

I suspect chainline and how far inward the FD is traveling...since in
the stand it's OK, but when lots of tension on the top part of the
chain, it's reluctant to come off.
Also may be FD alignment and/or height, making sure the 'bump' on FD is
against the chain when you shift. If the seatube angle is shallow, it
may not work well. May try to bend the 'nose' of the FD in a wee bit
also. FD outside cage should be aligned with the chain when in big ring
and small cog...that also 'encourages' the FD to move the chain to
smaller cogs..

If you have a 2 piece crank, yer pretty much SOL. BTW-A DA FD is not
compatible with shimano MTB shifters.

 

[Phil, Non-Squid]

Dave wrote:
> Phil, Non-Squid wrote:
>> When you said "their prescribed fix," who is "they?" Your LBS? I
>> would look for a second opinion.
>>
>> --
>> Phil
>
> Its a Klein Palomino, using a design licensed from Maverick. The poor
> front shifting is a known drawback of their "monolink" design,
> probably aggravated by Klein's implementation of it - I believe it is
> because the angle of the front der changes in relation to the chain
> as the shock compresses. They recommend DA triple FD's specifically
> because of the strong return spring.
>
> My problem, FWIW, is difficulty shifting from the middle to the small
> chainring under pressure. I shift, the FD releases and starts pushing
> the chain, yet the FD is unable to disengage the chain. If I continue
> pedaling a few more revs, I get chainsuck rather than a shift
>
> The FD is an XT and the crank is a Truvativ Firex Team.

Sometimes the little lip on the outer cage designed to push the chain down
from the middle to the small chainring can be carefully adjusted with an
additional inwards projection.

--
Phil

 

[Werehatrack]

On 16 Jan 2007 08:28:11 -0800, "Dave" <[email protected]> may have
said:

>
>Werehatrack wrote:
>> Presumably this is due to their having included too many sharp bends
>> in the cable path, a not-uncommon error.
>
>
>The cable routing is indeed circuitous, but the shifting problems occur
>only when going from middle to small ring under pressure. On level
>ground and on the stand, the shifting is perfect. Would you still
>suspect cable drag?

Yup. If the cable is not free-moving, it reduces the amount of force
available from the spring. On the stand, the amount of force needed
to move the chain while turning the crank is at its lowest because
there's no tension on the chain, and thus the der does not have to
apply as much force in order to get the chain to walk up and drop from
the middle sprocket to the small one. I had a low-end Pacific here
that produced similar symptoms until I put a decent fder cable on it,
at which point it shifted quite well indeed under load. Sometimes,
just oiling the cable and working the lube into the housing is enough
to get the problem to go away.

--
My email address is antispammed; pull WEEDS if replying via e-mail.
Typoes are not a bug, they're a feature.
Words processed in a facility that contains nuts.

 

[Bill Westphal]

Dave <[email protected]> wrote:
>
> Phil, Non-Squid wrote:
>> When you said "their prescribed fix," who is "they?" Your LBS? I would
>> look for a second opinion.
>>
>> --
>> Phil
>
> Its a Klein Palomino, using a design licensed from Maverick. The poor
> front shifting is a known drawback of their "monolink" design, probably
> aggravated by Klein's implementation of it - I believe it is because
> the angle of the front der changes in relation to the chain as the
> shock compresses. They recommend DA triple FD's specifically because
> of the strong return spring.
>
> My problem, FWIW, is difficulty shifting from the middle to the small
> chainring under pressure. I shift, the FD releases and starts pushing
> the chain, yet the FD is unable to disengage the chain. If I continue
> pedaling a few more revs, I get chainsuck rather than a shift
>
> The FD is an XT and the crank is a Truvativ Firex Team.
>

Interesting, I've got a 1-yr-old Mav 7/5, and at the time they
recommended an ultegra 3-sp FD, which I've got, with XTR + X.0, and
there isn't a problem downshifting the FD. In fact it works so well
my biggest problem is it throws the chain off when I'm climbing and
need that granny most (but never in the bike stand). I.e. it's very
strong and just snaps over to the left. I called wrenchscience about
the problem and they said Mav was now recommending the Shimano R773
for this reason, so I called Maverick (Ethan) and he confirmed that
was their new recommendation for all new Mav bikes. I guess it's
bigger cage is less likely to throw the chain. It actually takes
quite a bit of thumb strength (against that Ultegra FD spring) to
downshift it, and I sometimes shift the RD when a FD is more in order,
being more used to muscling it over with 2 fingers on a campy road
bike. I don't know if the Ultegra spring is the same as in the DA, or
how it compares to the R773, which Shimano advertises as for "flat
handlebar" bikes, although I don't see what the FD has to do with the
handlebars.

BTW, if I adjust the FD so that it just barely shifts to the granny
(to avoid throwing the chain), if I stand up out of the saddle and
lean forward uncompressing the rear shock it shifts right away, just
as in the stand, so the compression of the shock when you're trying to
shift is definitely a factor in whether it's going to shift too much,
too little, or just right. In fact I run the rear shock a little high
on pressure just for this reason. If I could get a working chain
catcher I could adjust the FD to shift too much and not worry about
it.

Maybe it's must be a problem with the cable routing on the Klein or
your FD. I put photos of my Maverick BB at
picasaweb.google.com/BillWestphal/MaverickBB for Nick at Jump Stop,
who was going to try to recommend some chain catcher, eventhough his
wouldn't work, and supposedly he's still working on it. You can see
something of how Maverick routes the cable (via a look on their
"D-Link" thingie that the braze-on FD attaches to) in the photos.

Bill Westphal

 

[James Thomson]

"Bill Westphal" <[email protected]> a écrit:

> I don't know if the Ultegra spring is the same as in the DA, or
> how it compares to the R773, which Shimano advertises as
> for "flat handlebar" bikes, although I don't see what the FD
> has to do with the handlebars.

Shimano flat bar and drop bar controls have generally used different amounts
of cable pull per shift for the front derailleur. The R773 is designed for
large (road-sized) chainrings, and flat bar cable pull.

James Thomson