Autoshifting on rebuilt Raleigh

bob said:

Thanks all for your comments on my rebuild. I now have a techy question.
I was giving said Raleigh its first proper tour last night when I found
a strange problem, namely the chain automatically shifting down a gear
and then immediately back up every now and again. It mostly happened
under what I like to think of as "power".

Now, the rear cassette (Tiagra) has 8 cogs which seems an awful lot to
me, but there you go, my mind is still in the 80's. Each shift seems to
coincide with a chain revolution. The transmission alignment seems to be
OK. So any ideas on the problem?

Some thoughts of mine. Is it because I'm using a non-indexed friction
shifter, that slight deviation from the rear cog being perfectly
selected causes the problem. Another possibility- the chain is fitted
with a Powerlink. This is a b****ck hair wider than the chain. Could
this be enough to cause an inadvertent shift?

Alternatively will the whole thing just bed down with a bit of wear?

Sheldon, as always, has a view. http://www.sheldonbrown.com/autoshift.html

--
Brian G
www.wetwo.co.uk

In message <[email hidden]>, Brian G
<[email hidden]> writes

Quoted message said:

bob said:

Thanks all for your comments on my rebuild. I now have a techy
question. I was giving said Raleigh its first proper tour last night
when I found a strange problem, namely the chain automatically
shifting down a gear and then immediately back up every now and
again. It mostly happened under what I like to think of as "power".
Now, the rear cassette (Tiagra) has 8 cogs which seems an awful lot
to me, but there you go, my mind is still in the 80's. Each shift
seems to coincide with a chain revolution. The transmission alignment
seems to be OK. So any ideas on the problem?
Some thoughts of mine. Is it because I'm using a non-indexed
friction shifter, that slight deviation from the rear cog being
perfectly selected causes the problem. Another possibility- the chain
is fitted with a Powerlink. This is a b****ck hair wider than the
chain. Could this be enough to cause an inadvertent shift?
Alternatively will the whole thing just bed down with a bit of wear?

Sheldon, as always, has a view. http://www.sheldonbrown.com/autoshift.html

I should have thought to look myself.

Cable guide now greased. I'll have to wait for it to dry before testing
however. I couldn't possibly get it wet and muddy just yet.
--
geomannie

in message <+GTWrACZOYvGFwdB@downie#n0sapm#.co.uk>, bob

('downiegeon0spam.co.uk@downie#n0sapm#.co.uk') said:

Thanks all for your comments on my rebuild. I now have a techy question.
I was giving said Raleigh its first proper tour last night when I found
a strange problem, namely the chain automatically shifting down a gear
and then immediately back up every now and again. It mostly happened
under what I like to think of as "power".

Sorry... but this is frame flex.

Steel frames of this vintage do flex. It's what makes them comfortable to
ride on less-than-perfect roads. Old five- and six- speed derailleurs were
much less sensitive, because it the cage had to move further to shift
gear. But the cable goes from the lever, under the bottom bracket, to the
mech, and as the frame flexes the points where the cable is held relative
to the frame move with respect to one another. It isn't very much... but
it doesn't need to be.

Quoted message said:

Now, the rear cassette (Tiagra) has 8 cogs which seems an awful lot to
me, but there you go, my mind is still in the 80's. Each shift seems to
coincide with a chain revolution. The transmission alignment seems to be
OK. So any ideas on the problem?

Some thoughts of mine. Is it because I'm using a non-indexed friction
shifter, that slight deviation from the rear cog being perfectly
selected causes the problem. Another possibility- the chain is fitted
with a Powerlink. This is a b****ck hair wider than the chain. Could
this be enough to cause an inadvertent shift?

Possible. The cassette will be ramped, and the slightly wider link may be
enough to catch the ramps.

But I think (my commuter bike is also an old steel Raleigh, though nothing
like as nice as yours) that it's frame flex.

--
[email hidden] (Simon Brooke) http://www.jasmine.org.uk/~simon/

;; Women are from Venus. Men are from Mars. Lusers are from Uranus.

On Sat, 11 Aug 2007 13:00:06 +0100, bob

downiegeon0spam.co.uk@downie#n0sapm#.co.uk said:

In message <[email hidden]>, Brian G
<[email hidden]> writes

Quoted message said:

bob said:

Thanks all for your comments on my rebuild. I now have a techy
question. I was giving said Raleigh its first proper tour last night
when I found a strange problem, namely the chain automatically
shifting down a gear and then immediately back up every now and
again. It mostly happened under what I like to think of as "power".
Now, the rear cassette (Tiagra) has 8 cogs which seems an awful lot
to me, but there you go, my mind is still in the 80's. Each shift
seems to coincide with a chain revolution. The transmission alignment
seems to be OK. So any ideas on the problem?
Some thoughts of mine. Is it because I'm using a non-indexed
friction shifter, that slight deviation from the rear cog being
perfectly selected causes the problem. Another possibility- the chain
is fitted with a Powerlink. This is a b****ck hair wider than the
chain. Could this be enough to cause an inadvertent shift?
Alternatively will the whole thing just bed down with a bit of wear?

Sheldon, as always, has a view. http://www.sheldonbrown.com/autoshift.html

I should have thought to look myself.

Cable guide now greased. I'll have to wait for it to dry before testing
however. I couldn't possibly get it wet and muddy just yet.

Shimano recommend setting the rear derailleur sprockets slightly towards the
next biggest cassette sprocket to prevent upshifting, see:

http://techdocs.shimano.com/media/techdocs/content/cycle/SI/105/RD-5500-5501/SI-5TK0D-En_v1_m56577569830603908.pdf

However Bob mentions downshifting under load which is very odd.

Neil

In message <[email hidden]>, Simon
Brooke <[email hidden]> writes

Quoted message said:

in message <+GTWrACZOYvGFwdB@downie#n0sapm#.co.uk>, bob

('downiegeon0spam.co.uk@downie#n0sapm#.co.uk') said:

Thanks all for your comments on my rebuild. I now have a techy question.
I was giving said Raleigh its first proper tour last night when I found
a strange problem, namely the chain automatically shifting down a gear
and then immediately back up every now and again. It mostly happened
under what I like to think of as "power".

Sorry... but this is frame flex.

Steel frames of this vintage do flex. It's what makes them comfortable to
ride on less-than-perfect roads. Old five- and six- speed derailleurs were
much less sensitive, because it the cage had to move further to shift
gear. But the cable goes from the lever, under the bottom bracket, to the
mech, and as the frame flexes the points where the cable is held relative
to the frame move with respect to one another. It isn't very much... but
it doesn't need to be.

Quoted message said:

Now, the rear cassette (Tiagra) has 8 cogs which seems an awful lot to
me, but there you go, my mind is still in the 80's. Each shift seems to
coincide with a chain revolution. The transmission alignment seems to be
OK. So any ideas on the problem?

Some thoughts of mine. Is it because I'm using a non-indexed friction
shifter, that slight deviation from the rear cog being perfectly
selected causes the problem. Another possibility- the chain is fitted
with a Powerlink. This is a b****ck hair wider than the chain. Could
this be enough to cause an inadvertent shift?

Possible. The cassette will be ramped, and the slightly wider link may be
enough to catch the ramps.

But I think (my commuter bike is also an old steel Raleigh, though nothing
like as nice as yours) that it's frame flex.

Thanks all. I think you've nailed it. Following Brian G's pointer to
Sheldon I greased the bottom bracket cable guides. Touch wood, having
given it a 10 mile spin, no autoshifting. I am guessing that friction
was ratcheting up the cable tension (downshift), then it snapping back
(upshift).

Cheer
--
geomannie