Weird gear happening.

[Milkfloat]

Is the shifter clicking down, or is the chain dropping down with the shifter still in 2 ?

Could be that your mech is badly adjusted. In normal use will it shift between all three easily.

The shifter is clicking down and the chain drops on the number 1 ring if that makes sense.

This is key - there is no way the chain would move chainring without the cranks being turned. Therefore, as well as the shifter movement the cranks must be turned as well. I refuse to believe that a stationary bike would change gear itself and have the cranks rotated.

 

[Milkfloat]

Cables stretch when you ride and shift the gears about, they then shrink back a bit when you leave them stood around. This has the same effect as moving the paddles.

If such a thing could occur then the gear would be moving the opposite to that detailed by the OP.

 

[Tim Hall]

fierce-sounding lab code-names

This bit is just great. (The rest wasn't bad either).

 

[Racing roadkill]

If such a thing could occur then the gear would be moving the opposite to that detailed by the OP.

If the mech remains in the same position (which it doesn't) due to the cable not stretching and compressing back uniformly enough relative to a better cable. Cheap / stretchy cables lead to ghost shifting, for the reasons I've detailed, it's the laws of physics / mechanics. If you need to argue, you should argue with a power ( even ) higher in the order of the universe than my good self.

 

[Milkfloat]

If the mech remains in the same position (which it doesn't) due to the cable not stretching and compressing back uniformly enough relative to a better cable. Cheap / stretchy cables lead to ghost shifting, for the reasons I've detailed, it's the laws of physics / mechanics. If you need to argue, you should argue with a power ( even ) higher in the order of the universe than my good self.

Could you explain how a cable on a front derailleur that 'shrinks' could move the derailleur from chainring 2 to 1, when to do so require less cable tension rather than more?

 

[Racing roadkill]

Could you explain how a cable on a front derailleur that 'shrinks' could move the derailleur from chainring 2 to 1, when to do so require less cable tension rather than more?

Well I could do, but it would be a waste of time, because you'd read the bit you wanted to, and ignore the important bit, then quote the wrong bit out of context, just to try and appear like a smart arse ( based on my experience thus far).

 

[Smithbat]

Umm, I didn't want to cause any trouble, I said that my gear thing was due to my own clumsiness and not that it was bewitched. Thanks all

 

[T4tomo]

Umm, I didn't want to cause any trouble, I said that my gear thing was due to my own clumsiness and not that it was bewitched. Thanks all

Don't stop the petty arguing just when it's getting going!

I quite like the sticky pawls theory personally, assuming it was only changing chainrings as you started to pedal. The sticky pawls may or not be aided by an un-noticed nudge on the trigger.

 

[Racing roadkill]

It will be the heat generated from the friction from all the shifting.

Or my in depth knowledge and expertise / experience of testing thousands of cable tension / spring tension related mechanisms / devices over decades, telling me that the problems described originally usually stem from less than ideal / non uniform behaviour of springs ( in the mech for example ) and cables, in a system that relies heavily on repeatable behaviour under stress / strain from those components.

 

[Racing roadkill]

Umm, I didn't want to cause any trouble, I said that my gear thing was due to my own clumsiness and not that it was bewitched. Thanks all

Don't worry, the usual trolls have come out from under their bridge, sit back and enjoy the ride, as I bitch slap them back from whence they came.

 

[Racing roadkill]

Of course sometimes the symptoms originally described can stem from ( for example ) leaning your bike against a wall, then having someone lean their bike against yours, and that resulting in the gear being changed, and you not noticing, until you ride off ( not that I've done that of course).

 

[Yellow Saddle]

Or my in depth knowledge and expertise / experience of testing thousands of cable tension / spring tension related mechanisms / devices over decades, telling me that the problems described originally usually stem from less than ideal / non uniform behaviour of springs ( in the mech for example ) and cables, in a system that relies heavily on repeatable behaviour under stress / strain from those components.

Your appeal to authority is quite astonishing, as is your silly application of vaguely engineering-sounding terminology.
Bitch-slapping ain't any good either. You will have to explain yourself.
Particularly:

• How the Young's modulus would affect a cable slowly losing tension.
• How repeated stress/strain cycles would lead to the phenomena described.
• How a cable not "compressing back uniformly" could create the phenomena.
• How you could compress a bicycle cable not restrained in a sleeve, as on a FD.
• How come you are so clever but cannot express the phenomena you believe in, in plain English.

You could of course just admit that it was all bullshit and you were just shitting us, but I doubt you will do that.

 

[Yellow Saddle]

[QUOTE 4529191, member: 9609"]I had this very problem, old dried out grease would either make the pawl not engage or engage poorly and likly to jump back out allowing the gears to go into low range. This was the culprit. You may get away or fix it for a while by spraying thin oil into it, but it is better to dismantle clean properly and re-grease.

[/QUOTE]

Yup, that's the one. I didn't want to scare the OP with disassembly but it is obviously the best solution in severe cases. Interesting enough, at the Shimano school they teach mechanics to spray the hell out of it until the fluid runs clear.

BTW, I now have your fingerprints on file. I see you have a few traffic fines outstanding.

 

[Yellow Saddle]

Could you explain how a cable on a front derailleur that 'shrinks' could move the derailleur from chainring 2 to 1, when to do so require less cable tension rather than more?

How dare you ask a question of logic? Are you a smartarse or some such?

 

[S-Express]

Cables stretch when you ride and shift the gears about, they then shrink back a bit when you leave them stood around. This has the same effect as moving the paddles.