Phantom gear shifts

sannesley

Well-Known Member
Location
Northern Ireland
I went out on Friday and covered 42 miles. halfway through the run the gears on the rear cassette started to shift on their own up and down. They only seemed to shift between one cog either side (if that makes sense) and didn't jump multiple cogs. It happened a number of times and sometimes if going up a hill the phantom change sounded very hard on the rear cassette.

The run on Friday means the bike has covered around 120 miles in total. I think that it's cable stretch causing it as the bike is only a few months old. Is it something I can fix myself or would I be better to take it to the Local Bike shop?
 

mjr

Comfy armchair to one person & a plank to the next
Fiddly but fixable yourself. Www.SheldonBrown.com or www.ParkTool.com should have info, depending how hipster you are. ;)

Probably just a barrel adjustment but might need cable tension taking up again.
 
Location
Loch side.
I went out on Friday and covered 42 miles. halfway through the run the gears on the rear cassette started to shift on their own up and down. They only seemed to shift between one cog either side (if that makes sense) and didn't jump multiple cogs. It happened a number of times and sometimes if going up a hill the phantom change sounded very hard on the rear cassette.

The run on Friday means the bike has covered around 120 miles in total. I think that it's cable stretch causing it as the bike is only a few months old. Is it something I can fix myself or would I be better to take it to the Local Bike shop?
You don't say what type of bike it is but if it is a road bike with naked cables sliding in a slider under the bottom bracket, have a look there. Sugary drinks leak from the water bottle and the drink runs all the way down the frame and settles on that slider, where the water evaporates and the syrup remains. This causes delayed shifting and ghost shifting with flexible frames under hard riding.

In that case, water is your friend. Slacken the cables without pedaling, so that the derailers can't move. This will give you cable slack and enough space to get in with a brush and water.
 
OP
sannesley

sannesley

Well-Known Member
Location
Northern Ireland
You don't say what type of bike it is but if it is a road bike with naked cables sliding in a slider under the bottom bracket, have a look there. Sugary drinks leak from the water bottle and the drink runs all the way down the frame and settles on that slider, where the water evaporates and the syrup remains. This causes delayed shifting and ghost shifting with flexible frames under hard riding.

In that case, water is your friend. Slacken the cables without pedaling, so that the derailers can't move. This will give you cable slack and enough space to get in with a brush and water.
The bike is a Giant Defy 3 2015. I checked for the sugary drinks but could see no evidence of that being the cause of the problem :sad:
 
Location
Loch side.
The bike is a Giant Defy 3 2015. I checked for the sugary drinks but could see no evidence of that being the cause of the problem :sad:
OK. Ghost shifting is related to cable friction. Somewhere in your cable there is friction. Are you confident enough with DIY to release the cable on the back derailer and get it back on, doing a full adjustment from scratch? If so, then I'll proceed.
 
Location
Pontefract
Uh oh. He mentioned cable stretch....
Who did. I can't see owt.

Basically, clean off any crud on the inner cables, and where it runs under the BB, I use GT85 on the cables and run them through the cables a few time dry off with a clean cloth the re-attach everything.
 
Last edited:
OP
sannesley

sannesley

Well-Known Member
Location
Northern Ireland
OK. Ghost shifting is related to cable friction. Somewhere in your cable there is friction. Are you confident enough with DIY to release the cable on the back derailer and get it back on, doing a full adjustment from scratch? If so, then I'll proceed.
I'm confident enough with DIY but not bike related DIY. I took it to the LBS this morning and he had a look at it and I think he worked with the barrel adjuster on the rear derailer. I was thinking of buying a DIY guide for bike maintainence. Does anyone have any experience of this book?

http://www.haynes.co.uk/bikebook/
 
I'm confident enough with DIY but not bike related DIY. I took it to the LBS this morning and he had a look at it and I think he worked with the barrel adjuster on the rear derailer. I was thinking of buying a DIY guide for bike maintainence. Does anyone have any experience of this book?

http://www.haynes.co.uk/bikebook/
I wouldn't bother with the book, just youtube it. Watch several videos and you will get a better idea than you would with text and pictures .
 
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