Bicycle Chain flaps when I freewheel

fender

I have a mountain bike I ride.

When I freewheel it such as downhill, the chain slackens and sags and flaps. This is rather worrying. Any idea what is wrong and how I should fix it?

Thanks.

:money::money::money:

maninthestreet

Is the rear wheel seated far back enough in it's locating slot? If it is, then it sounds like you need to remove a link or two for the chain.

Strider590

The rear derailleur should take up any slack in the chain if it's adjusted correctly (the spring loaded bit with the 2 small cogs pull the chain tight).
The chain may also (as mentioned) have too many links.

If it's a cheap bike from a catalogue or Halfrauds then it probably both of the above.

If its a cheap full suspension bike then every compression of the rear will reduce the tension on the chain and cause it to flap about.
The proper FS beasts use complex suspension geometry and multiple links to keep equal tension on the chain at all times.






Does it still flap about when in top gear (on the front)?

fender

It only has five gears.

Strider590

^^ None at the front? O_o

Is it old? has the chain stretched?

Oil up that rear derailleur bit, make sure the that part I mentioned isn't rusted and unable to pull it tight.

fender

Yes, this is an old bike. I have previously oiled the derailleur, did no good. I will try and get that back wheel pushed further back.
Thanks.

Pew_Pew_Pew_Lasers!

The position of the wheel will make little difference. The rear mech is spring-loaded to take up the slack when cycling:

http://www.youtube.com/watch?v=AZQf1bduGYs

Take the chain off the front cog. If the rear mech springs back, its fine. If its slow or sticky, it needs freeing up.

The chain may be too long, but the rear mech is the first thing to check.

sequence

Could be the spring has snapped in the deraileur, has happened to me before. It also could be the pawls in your freewheel are sticking, that will push the chain loose when you freewheel. Does the freewheel turn backwards ok ?

forgotmyname

Probably 20 years old & never been serviced, The bearings are dry.

They need some fresh grease which it not a sticky goo.