Automatic shifting prob

[rich p]

Here's a new one on me. 3 times in the past 2 weeks, I have shifted from the middle ring to the large one without touching the shifter. The first time I thought it was a slight touch by mistake but not so.

Any ideas?

I've cleaned the front derailleur already.

I'll change the cable, tension and outer but does it sound like a shifter problem? That is obviously a more expensive solution that I'd like to avoid.

 

[tyred]

Self shifting can be caused by a sticking cable combined with frame flex.

 

[MacB]

Self shifting can be caused by a sticking cable combined with frame flex.

So Rich is just laying too much power through the frame, maybe he needs to go to Fixed.

 

[rich p]

So Rich is just laying too much power through the frame, maybe he needs to go to Fixed.

Cheers Al, but you're right! I need to get fixed

I'll see what the new cable and outer does tyred. Ta

 

[potsy]

Not wanting to hijack your thread or anything, but, should you always replace the cable outers at the same time as buying new inners?

 

[Crackle]

Oy, MrP. Whilst researching my own problem I came across this by good old Sheldon. It recommends greasing the bb cable guide and expands a bit on what tyred said.

 

[rich p]

Not wanting to hijack your thread or anything, but, should you always replace the cable outers at the same time as buying new inners?

I don't always Potsy but I usually give them a squirt while they're off.

 

[I like Skol]

Is the bottom bracket in tip-top shape? if there is any play in the bearings there it might not be noticable/noisy while riding but could allow freak gear changes.

 

[gwhite]

I don't get this as the default position for the FD is the one nearest the frame.Any other position needs the cable to be tensioned.

 

[rich p]

I don't get this as the default position for the FD is the one nearest the frame.Any other position needs the cable to be tensioned.

Quite so, hence my puzzlement! If Sheldon says it's possible thoufgh I'll go along with it and it definitely happened!

I have todaycleaned and greased the bottom bracket cable guide, new cable and outers - so time will tell.

I think the BB is okay AFAIK Skol.

 

[gwhite]

Quite so, hence my puzzlement! If Sheldon says it's possible thoufgh I'll go along with it and it definitely happened!

I have todaycleaned and greased the bottom bracket cable guide, new cable and outers - so time will tell.

I think the BB is okay AFAIK Skol.

The Sheldon quote refers to the rear DR and the chain moving to the smaller sprocket i.e. to the RD's default position and with the spring tension.You, on the other hand, appear to talking about the FD, and the chain moving to the larger ring. Two very different things and I can see no way the Front Der. cage can move the chain to the Large ring when the lever is not being moved as this would be against the spring tension of the FD

 

[frank9755]

Rich,
I read this one a couple of days ago and had a thought. I didn't post it as I thought someone would be along with a better answer but, as they haven't, here goes.

My thought was that your cable might be adjusted slightly too tightly so that when you are in the middle ring you are always just a hairs breadth away from an upshift. A small bit of frame flex or bottom bracket play as you put the power down would then trigger the shift...

I have to admit, writing it out seems unlikely!

If this was the case you would most likely be getting mech-rub when in the middle ring and a small sprocket. Is this happening?

Thinking faster than I type, if there are patterns to when it does happen, it might lead to a better answer, eg:
Just after you have done a rear shift and the chain is bouncing around a bit
When you are in a particular rear sprocket (more likely to be a high one than a low one by my theory)
When you are pedalling hard
On the right or left foot pedal stroke?

Good luck with it

Frank

 

[deaksie]

Hiya
I have a similar problem but mine is on the rear cassette.
I'll be cycling along on the flat (or uphill) perfectly happily and then it will just suddenly change up on its own - it's happening in the top few gears -
The bike was serviced about 3 weeks ago and had a new cassette, chain, cables etc. It's been back and forth to the bike shop but we can't work out what's wrong with it.
The other day we discovered a seized jockey wheel which has been replaced, and I really thought this would solve the problem, but it hasn't. I rode today for an hour and at one stage it was changing up and down with every stroke, but then it was fine again for 20 mins, and then started doing it again. really odd. I'm not leaning on the shifter or anything daft honest!
Has anyone come across this before? - I'd be really grateful for any suggestions
Unfortunately, I've organised a charity bike ride for next weekend so I could do with some help quick
Many thanks
L

 

[HLaB]

Hiya
I have a similar problem but mine is on the rear cassette.
I'll be cycling along on the flat (or uphill) perfectly happily and then it will just suddenly change up on its own - it's happening in the top few gears -
The bike was serviced about 3 weeks ago and had a new cassette, chain, cables etc. It's been back and forth to the bike shop but we can't work out what's wrong with it.
The other day we discovered a seized jockey wheel which has been replaced, and I really thought this would solve the problem, but it hasn't. I rode today for an hour and at one stage it was changing up and down with every stroke, but then it was fine again for 20 mins, and then started doing it again. really odd. I'm not leaning on the shifter or anything daft honest!
Has anyone come across this before? - I'd be really grateful for any suggestions
Unfortunately, I've organised a charity bike ride for next weekend so I could do with some help quick
Many thanks
L

It might not be the issue but my sirrus was doing something similar before I made the gear cable outer that loops to the rear deraileur a bit longer (less of a tight radius). I had just previously replaced both inners and outers but found that made no difference untill I loosened the loop.

 

[frank9755]

Hiya
I have a similar problem but mine is on the rear cassette.
I'll be cycling along on the flat (or uphill) perfectly happily and then it will just suddenly change up on its own - it's happening in the top few gears -
The bike was serviced about 3 weeks ago and had a new cassette, chain, cables etc. It's been back and forth to the bike shop but we can't work out what's wrong with it.
The other day we discovered a seized jockey wheel which has been replaced, and I really thought this would solve the problem, but it hasn't. I rode today for an hour and at one stage it was changing up and down with every stroke, but then it was fine again for 20 mins, and then started doing it again. really odd. I'm not leaning on the shifter or anything daft honest!
Has anyone come across this before? - I'd be really grateful for any suggestions
Unfortunately, I've organised a charity bike ride for next weekend so I could do with some help quick
Many thanks
L

Sounds like your indexing isn't quite right. Have you tried adjusting it?
NB - you have hijacked Rich's thread; usually its best to start your own!