top chain run goes slack...

[Maz]

...when pedalling backwards.

This morning (first ride since xmas break), when I turned the right pedal backwards ready to push off, the top chain run went slack and the cassette wouldn't turn round. Then, later on, it was working OK.

What might have caused this? More importantly, how can I fix this? Thank you.

 

[Globalti]

It's usually caused by friction in the freewheel or in the derailleur pulleys. Possibly damp has got into the freehub and rusted it a bit or the grease has hardened up and got sticky. In very cold weather the freewheel can actually freeze. You probably found that it turned backwards more readily with the chain on a big cog, where it had more leverage.

If you can remove the cassette, do so, then remove the freehub, which is usually done with a big Allen key down the hole. If it's gritty and wobbly it ought to be replaced, if not you might be able to revive it by flooding it with a very light lube like WD40 then dribbling in a heavier lube like 3 in 1 oil. Trying to do this with a dirty cassette in place will just drive more dirt into the freehub.

 

[fossyant]

You had problems before Christmas - this is re-occuring ! Time for a strip down rather than running oil into it.

 

[Broadside]

My bike does this if there is not enough lube on the chain but usually free's up after a few rotations of the pedals forwards.

 

[Maz]

Thanks for the help, everyone.
Brace yourself for some ugly photo uploads when it all goes tits-up and I ask for more help.
Cheers

 

[fossyant]

Thanks for the help, everyone.
Brace yourself for some ugly photo uploads when it all goes tits-up and I ask for more help.
Cheers

Fire away !!! Got the 10mm allen key ?

 

[fossyant]

If you can remove the cassette, do so, then remove the freehub, which is usually done with a big Allen key down the hole. If it's gritty and wobbly it ought to be replaced, if not you might be able to revive it by flooding it with a very light lube like WD40 then dribbling in a heavier lube like 3 in 1 oil. Trying to do this with a dirty cassette in place will just drive more dirt into the freehub.

This ^ - take the cassette and freehub off (you'll need to remove axel and bearings so watch for dropping balls !)

 

[Maz]

Fire away !!! Got the 10mm allen key ?

The last wheel (Mavic?) was bigger than 10mm, so couldnt get the freehub off.
I hope this one (Shimano R500) has a freehub that will come off with a 10mm allen key.

 

[snorri]

This morning (first ride since xmas break),

This is the crux of the problem, 'xmas break'.
Your bicycle is understandably a little peeved at being ignored for nearly two weeks and is telling you so in the only way it knows how.