"Slack" Rear derailleur

[Little Jim]

My rear derailleur is no longer keeping the chain taut when on small-small gear combinations - by this I mean that the chain will rest on the top of the chain stay if I'm free wheeling.  The problem is mainly when I am on the small front ring (39 tooth) and the outer three rear cogs (and, yes, I know that I shouldn't really use the smal-small combination).  The derailleur is about 8 or 10 years old and will have done in the order of 10 000 miles.  So should I just bite the bullet and buy a new one, or is it worth taking it off and giving it a good clean?

[Torslanda]

By all means clean it first. Use a good cleaner like the Finish Line citrus based one but if it really is that baggy then I think its time for a new one.

[Polar Bear]

I have found similar problems with ageing mechs.   Dismantling and cleaning the spring which sits around the frame bolt helps in my experience.

[Ian H]

Check it's not the freehub/freewheel getting stiff. If the chain goes slack when you back-pedal, it might not be the mech.

[Crepello]

Check it's not the freehub/freewheel getting stiff. If the chain goes slack when you back-pedal, it might not be the mech.

+1