rear derailer help

48 views
Skip to first unread message

Ted Heise

unread,
Aug 29, 2021, 3:31:47 PMAug 29
to

Hi all,

Looking for a little help with a tandem mechanical problem.

Kathy and I foundered while standing to climb a steep hill last
weekend when the rear chain started skipping. I suspected chain
(and probably cassette) wear, so I put on a new set this morning.
It's hard for me to tell cog wear, but the two chains I alternate
were in the vicinity of 12 3/16 inches or a bit more for 12 links.
So they were definitely shot.

We went out again today, and it still acted up when standing on a
hill. I think what's happening is less skipping and more like
ghost shifting. I did notice that after it had "skipped" last
week, the chain ended up on a cog much smaller than I'd had it on
before acting up. So I'm thinking the rear derailer is the
culprit.

We're running an Ultegra RD-6700A longer arm (GS) component, but
can't seem to find that specific model. We have a 10-speed 11-32
cassette and an Ultegra shifter. Can anyone suggest where I might
find this rear derailer part (or equivalent)? My searches all
seem to turn up the RD-8000, maybe that will work?

Alternatively, is it possible to repair the rear der? It has a
fair bit of side to side play in the cage, and I think it is
flexing out of position when we are honking on it up hills.
We're not a real heavy team (maybe 320 pounds combined), but do
generate a lot of torque. Maybe the rivets in the parallelogram
can be peened into being tighter?

Thanks for any suggestions!

--
Ted Heise <the...@panix.com> West Lafayette, IN, USA


Lou Holtman

unread,
Aug 29, 2021, 3:49:09 PMAug 29
to

jbeattie

unread,
Aug 29, 2021, 3:59:00 PMAug 29
to
Also, before switching out the derailleur, I'd look carefully at the cable. Sticking under the BB can cause ghost shifting when the BB is flexed (standing out of the saddle), and impending cable failure can cause odd shifting issues, although short term before it breaks. I'd also check the hanger to make sure it is straight. Wearing out the RD would be further down the list for me, and it would manifest as sloppiness in or out of the saddle -- noise, having to over-shift to get a gear. It wouldn't be limited to riding out of the saddle, IMO. Plus, derailleurs have a really long service life.

-- Jay Beattie.



AMuzi

unread,
Aug 29, 2021, 4:26:09 PMAug 29
to
No practical path for restoring sloppy parallelogram pivots
but that may not be the problem. If you hold the lower
roller area and move in and out (toward and away from the
wheel) the slop is usually in the upper pivot. Check that.

Since excessive play may probably present but unlikely to be
enough to prevent shifting, get your head behind the changer
(move the bike) to sight the cage against the chainrings. A
bent gear tab is more likely.

A sticking or kinked gear wire or damaged casing should also
be eliminated as a cause before panic or throwing parts at this.

--
Andrew Muzi
<www.yellowjersey.org/>
Open every day since 1 April, 1971


Ted Heise

unread,
Aug 29, 2021, 8:50:11 PMAug 29
to
On Sun, 29 Aug 2021 12:58:58 -0700 (PDT),
jbeattie <jbeat...@msn.com> wrote:
> On Sunday, August 29, 2021 at 12:49:09 PM UTC-7, lou.h...@gmail.com wrote:
> > On Sunday, August 29, 2021 at 9:31:47 PM UTC+2, Ted Heise wrote:

> > > Kathy and I foundered while standing to climb a steep hill
> > > last weekend when the rear chain started skipping. I
> > > suspected chain (and probably cassette) wear, so I put on a
> > > new set this morning.

> > > We went out again today, and it still acted up when standing
> > > on a hill. I think what's happening is less skipping and
> > > more like ghost shifting. I did notice that after it had
> > > "skipped" last week, the chain ended up on a cog much
> > > smaller than I'd had it on before acting up. So I'm thinking
> > > the rear derailer is the culprit.

> > > Thanks for any suggestions!
Lou, this seems to be something different from either the RD-6700A
I currently have or the RD-8000 I asked about. But it does sound
as if it would be compatible with my cssette from the description.
Thanks!


> Also, before switching out the derailleur, I'd look carefully
> at the cable. Sticking under the BB can cause ghost shifting
> when the BB is flexed (standing out of the saddle)

I regularly put a bit of Krylon teflon lube on the shift cables
where they go under each of the bottom brackets, as well as midway
between where they cross. So I doubt it's that.


> impending cable failure can cause odd shifting issues, although
> short term before it breaks. I'd also check the hanger to make
> sure it is straight.

This is a possibility, though I have some doubts. I've had cable
wear problems before, and it manifested quite differently. I do
plan to get the derailer hanger checked out, and also to replace
the cables and housing. They are approaching 10 years old, and
the cables in particular are pretty beat up adjacent to the
splitters.


> ...Wearing out the RD would be further down the list for me,
> and it would manifest as sloppiness in or out of the saddle --
> noise, having to over-shift to get a gear. It wouldn't be
> limited to riding out of the saddle, IMO.

The derailer has gradually needed overshifting in more and more
gears, especially at the ends of the cassette. Once it's in a
gear it's usually fine, except for this jumping skipping stuff.
Mostly on the smaller cogs.

Thanks for the suggestions!

Ted Heise

unread,
Aug 29, 2021, 8:56:22 PMAug 29
to
On Sun, 29 Aug 2021 15:26:06 -0500,
AMuzi <a...@yellowjersey.org> wrote:
> On 8/29/2021 2:31 PM, Ted Heise wrote:

> > Kathy and I foundered while standing to climb a steep hill
> > last weekend when the rear chain started skipping. I
> > suspected chain (and probably cassette) wear, so I put on a
> > new set this morning.

> > We went out again today, and it still acted up when standing
> > on a hill. I think what's happening is less skipping and more
> > like ghost shifting. I did notice that after it had "skipped"
> > last week, the chain ended up on a cog much smaller than I'd
> > had it on before acting up. So I'm thinking the rear derailer
> > is the culprit.

> > Alternatively, is it possible to repair the rear der?

> No practical path for restoring sloppy parallelogram pivots but
> that may not be the problem. If you hold the lower roller area
> and move in and out (toward and away from the wheel) the slop
> is usually in the upper pivot. Check that.

Yes, upper pivot, or even higher than that is where the play seems
to be greatest.


> Since excessive play may probably present but unlikely to be
> enough to prevent shifting, get your head behind the changer
> (move the bike) to sight the cage against the chainrings. A
> bent gear tab is more likely.

To be clear, I'm not really seeing difficulty in shifting--it's
only skipping/jumping when under heavy load, and seemingly with
the chain well seated on the cog selected. Will give the
alignment another look, the suggestion to check it against the
chainrings is very helpful. But not tonight. Garage is still
pretty hot.

And for what it's worth, the shifting today was better with the
new (and clean!) chains and cassette.


> A sticking or kinked gear wire or damaged casing should also be
> eliminated as a cause before panic or throwing parts at this.

Yes, will definitely plan to look at that as well, as noted else
thread.

Thanks for the great advice, Andrew!

Ted Heise

unread,
Sep 12, 2021, 4:02:22 PMSep 12
to
On Mon, 30 Aug 2021 00:56:19 -0000 (UTC),
Ted Heise <the...@panix.com> wrote:
> On Sun, 29 Aug 2021 15:26:06 -0500,
> AMuzi <a...@yellowjersey.org> wrote:
> > On 8/29/2021 2:31 PM, Ted Heise wrote:
>
> > > Kathy and I foundered while standing to climb a steep hill
> > > last weekend when the rear chain started skipping. I
> > > suspected chain (and probably cassette) wear, so I put on a
> > > new set this morning.

> > No practical path for restoring sloppy parallelogram pivots
> > but that may not be the problem. If you hold the lower roller
> > area and move in and out (toward and away from the wheel) the
> > slop is usually in the upper pivot. Check that.
>
> Yes, upper pivot, or even higher than that is where the play
> seems to be greatest.

> > A sticking or kinked gear wire or damaged casing should also
> > be eliminated as a cause before panic or throwing parts at
> > this.
>
> Yes, will definitely plan to look at that as well, as noted
> else thread.

Just to follow up on this, the fellow I bought the tandem from had
the same rear derailer in stock, and brought it along to the
Midwest Tandem Rally last weekend. He's been selling and
servicing tandems for decades, and said he'd never seen one with
so much side to slide play in it.

I threw the new part at it, and the need for overshifting is
nearly gone. I expect that to get better when I replace the
cables and housing. More importantly, we were able to stand on it
with pretty good force, and had no skipping or unexpected jumping
of the chain to a smaller cog.

As an aside, on the Sunday long route we hooked onto a fast group
of tandems and were running along in the mid to upper 20s for
quite a few miles. Fun!

Tom Kunich

unread,
Sep 12, 2021, 4:15:27 PMSep 12
to
Ted, because derailleurs were a relatively new technology, this stuff is beginning to gather age and so we should understand that you buy new whenever appropriate and THROW AWAY older components. Too many of them are being sold on Craigslist or Ebay when you usually don't pay for the shipping and/or taxes or gas to go an pick them up.

bob prohaska

unread,
Sep 12, 2021, 6:23:25 PMSep 12
to
Ted Heise <the...@panix.com> wrote:
> fair bit of side to side play in the cage, and I think it is
> flexing out of position when we are honking on it up hills.
>

Given that the derailer is on the slack side of the chain it's
hard to understand how the driving torque could have much effect.

If the chain skips, that might yank on the slack side and flex
the derailer momentarily, but that's not the derailer's fault.
Likewise, a loose axle might slip forward under heavy chain
tension and make mischief, but that (I think) would be visible.

If I'm missing something please point it out!

bob prohaska

Roger Merriman

unread,
Sep 13, 2021, 2:43:24 AMSep 13
to
I’ve had ones on the commute bike that have just worn out or rather very
sloppy and sluggish, again fitting a new one was a quick easy fix.

Roger Merriman.

Ted Heise

unread,
Sep 13, 2021, 7:45:04 AMSep 13
to
I'm not exactly sure what you're trying to say, Tom. I have no
interest in selling used parts, not least because it's not worth
my time. In this case, I'll likely keep the old part around, just
as a backup. It was actually bought to replace a similar part
that had broken in the middle of the body--probably due to some
defect in the part. I may look for an additional new one, just to
have on hand. If so, I would trash the old one.

Tom Kunich

unread,
Sep 13, 2021, 11:04:04 AMSep 13
to
A good set of 10 speed Record carbon shifters IS worth your while, believe me. Usable carbon 10 speed Record rear derailleur and a compact front derailleur as well. A set of these could sell for $700 quite easily. Because of this the cheaper Shimano crap is also sold for far more than it is worth and most of it is well worn.
Reply all
Reply to author
Forward
0 new messages