Shimano M781 derailleur, guide worn off, does it matter?

Folks,

A week ago I noticed that the little guide or whatever that is between
the two derailleur wheels has worn away on my MTB. It's simply ... gone.
You can see it in the oblong cut-out in the photo:

http://www.merlincycles.com/shimano-...ech-58066.html

I guess 2000mi of major chain slapping was too much for it. Anyhow,
what's its purpose? I haven't noticed any difference in riding or
shifting behavior.

--
Regards, Joerg

http://www.analogconsultants.com/

Joerg wrote:
Folks,

A week ago I noticed that the little guide or whatever that is between
the two derailleur wheels has worn away on my MTB. It's simply ... gone.
You can see it in the oblong cut-out in the photo:

http://www.merlincycles.com/shimano-...ech-58066.html

I guess 2000mi of major chain slapping was too much for it. Anyhow,
what's its purpose? I haven't noticed any difference in riding or shifting behavior.


Its purpose in life is to make an awful noise when you thread the chain
through the dérailleur improperly. At least, that's the only purpose I've
discovered.

On 31/07/2015 2:44 PM, Ralph Barone wrote:
Joerg wrote:
Folks,

A week ago I noticed that the little guide or whatever that is between
the two derailleur wheels has worn away on my MTB. It's simply ... gone.
You can see it in the oblong cut-out in the photo:

http://www.merlincycles.com/shimano-...ech-58066.html

I guess 2000mi of major chain slapping was too much for it. Anyhow,
what's its purpose? I haven't noticed any difference in riding or shifting behavior.


Its purpose in life is to make an awful noise when you thread the chain
through the dérailleur improperly. At least, that's the only purpose I've
discovered.

And if you do thread the chain improperly the awful noise stops after a
few dozen miles. It stops faster with an alloy cage.
PH

On 7/31/2015 12:44 AM, Ralph Barone wrote:
Joerg wrote:
Folks,

A week ago I noticed that the little guide or whatever that is between
the two derailleur wheels has worn away on my MTB. It's simply ... gone.
You can see it in the oblong cut-out in the photo:

http://www.merlincycles.com/shimano-...ech-58066.html

I guess 2000mi of major chain slapping was too much for it. Anyhow,
what's its purpose? I haven't noticed any difference in riding or shifting behavior.


Its purpose in life is to make an awful noise when you thread the chain
through the dérailleur improperly. At least, that's the only purpose I've
discovered.

I thought it was a safety device, to scare away mountain lions. One
should never ride without it.

--
- Frank Krygowski

On 2015-07-30 9:44 PM, Ralph Barone wrote:
Joerg wrote:
Folks,

A week ago I noticed that the little guide or whatever that is between
the two derailleur wheels has worn away on my MTB. It's simply ... gone.
You can see it in the oblong cut-out in the photo:

http://www.merlincycles.com/shimano-...ech-58066.html

I guess 2000mi of major chain slapping was too much for it. Anyhow,
what's its purpose? I haven't noticed any difference in riding or shifting behavior.


Its purpose in life is to make an awful noise when you thread the chain
through the dérailleur improperly. At least, that's the only purpose I've
discovered.


That must grind awfully. I can't see any sense in that thing. Maybe to
prevent a slapping chain from being sucked under in upper cage cog a
second time? Never had that happen and most of my rides with the MTB
cause lots of chain slap. Then one would expect to be able to mount a
protector like people do for the right chain stay.

--
Regards, Joerg

http://www.analogconsultants.com/

Frank Krygowski wrote:
On 7/31/2015 12:44 AM, Ralph Barone wrote:
Joerg wrote:
Folks,

A week ago I noticed that the little guide or whatever that is between
the two derailleur wheels has worn away on my MTB. It's simply ... gone.
You can see it in the oblong cut-out in the photo:

http://www.merlincycles.com/shimano-...ech-58066.html

I guess 2000mi of major chain slapping was too much for it. Anyhow,
what's its purpose? I haven't noticed any difference in riding or shifting behavior.


Its purpose in life is to make an awful noise when you thread the chain
through the dérailleur improperly. At least, that's the only purpose I've
discovered.

I thought it was a safety device, to scare away mountain lions. One
should never ride without it.


Worked for me.

On Fri, 31 Jul 2015 10:00:56 -0400, Frank Krygowski
wrote:

On 7/31/2015 12:44 AM, Ralph Barone wrote:
Joerg wrote:
Folks,

A week ago I noticed that the little guide or whatever that is between
the two derailleur wheels has worn away on my MTB. It's simply ... gone.
You can see it in the oblong cut-out in the photo:

http://www.merlincycles.com/shimano-...ech-58066.html

I guess 2000mi of major chain slapping was too much for it. Anyhow,
what's its purpose? I haven't noticed any difference in riding or shifting behavior.


Its purpose in life is to make an awful noise when you thread the chain
through the dérailleur improperly. At least, that's the only purpose I've
discovered.

I thought it was a safety device, to scare away mountain lions. One
should never ride without it.

It appears to be a "spacer" which prevents the two arms of the chain
tensioner from being squeezed together, jamming either the chain or
the idler pulleys.
--
cheers,

John B.

On 2015-07-31 5:58 PM, John B. Slocomb wrote:
On Fri, 31 Jul 2015 10:00:56 -0400, Frank Krygowski
wrote:

On 7/31/2015 12:44 AM, Ralph Barone wrote:
Joerg wrote:
Folks,

A week ago I noticed that the little guide or whatever that is between
the two derailleur wheels has worn away on my MTB. It's simply ... gone.
You can see it in the oblong cut-out in the photo:

http://www.merlincycles.com/shimano-...ech-58066.html

I guess 2000mi of major chain slapping was too much for it. Anyhow,
what's its purpose? I haven't noticed any difference in riding or shifting behavior.


Its purpose in life is to make an awful noise when you thread the chain
through the dérailleur improperly. At least, that's the only purpose I've
discovered.

I thought it was a safety device, to scare away mountain lions. One
should never ride without it.

It appears to be a "spacer" which prevents the two arms of the chain
tensioner from being squeezed together, jamming either the chain or
the idler pulleys.


Like after a crash or if something hits the derailleur cage? The little
lip that is no more never touched the other half of the cage, there used
to be a small gap of 0.040" or so.

If it is important I could drill a hole and mount a standoff or something.

--
Regards, Joerg

http://www.analogconsultants.com/

On Sat, 01 Aug 2015 07:30:24 -0700, Joerg
wrote:

Like after a crash or if something hits the derailleur cage? The little
lip that is no more never touched the other half of the cage, there used
to be a small gap of 0.040" or so.

The gap is to prevent chattering from vibration should the bolts
holding the idler pulleys become loose.

If it is important I could drill a hole and mount a standoff or something.

That would:
1. Add weight (standoff, mounting bolt, lock washer, nut, locknut,
etc).
2. Add costs (standoff, mounting bolt, lock washer, nut, locknut,
etc in added parts).
3. Create a stress riser at the mounting hole which will eventually
crack.

Methinks you'll find a simple collar pin easier, more common, and
somewhat cheaper:
http://brimages.bikeboardmedia.netdna-cdn.com/wp-content/uploads/2012/12/2013-Dura-Ace-9000-rear-derailleur-photos02.jpg
Note that the pins do not need to be secured by any manner of
fastener. The parallel side plates of the derailleur hold the pins in
place with the idler pulley hardware securing the side plates at the
required spacing.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On 2015-08-01 1:43 PM, Jeff Liebermann wrote:
On Sat, 01 Aug 2015 07:30:24 -0700, Joerg
wrote:

Like after a crash or if something hits the derailleur cage? The little
lip that is no more never touched the other half of the cage, there used
to be a small gap of 0.040" or so.

The gap is to prevent chattering from vibration should the bolts
holding the idler pulleys become loose.


Strange. I'd _want_ to hear such chattering because if a bolt becomes
loose and falls off on a trail that would mean I'd have to walk out.
Easily 15-20 miles which isn't fun.


If it is important I could drill a hole and mount a standoff or something.

That would:
1. Add weight (standoff, mounting bolt, lock washer, nut, locknut,
etc).
2. Add costs (standoff, mounting bolt, lock washer, nut, locknut,
etc in added parts).
3. Create a stress riser at the mounting hole which will eventually
crack.

Methinks you'll find a simple collar pin easier, more common, and
somewhat cheaper:
http://brimages.bikeboardmedia.netdna-cdn.com/wp-content/uploads/2012/12/2013-Dura-Ace-9000-rear-derailleur-photos02.jpg
Note that the pins do not need to be secured by any manner of
fastener. The parallel side plates of the derailleur hold the pins in
place with the idler pulley hardware securing the side plates at the
required spacing.


Possible. Although on an MTB everything that isn't welded or torqued
down real good tends to come off.

--
Regards, Joerg

http://www.analogconsultants.com/