Rear derailleur problem only when shifting down

[facelikebambi]

Hi

Total newbie here. Recently bought a second-hand bike with 18 gears, Shimano Revoshift grip shifters and Shimano RD-TY18 derailleur.

When in highest gear, I get a loud rattle after shifting down (to 5 or 4 rear cogs). On closer inspection, the chain looks like it wants to skip off the cog as it turns. Not sure what the technical term is, it kind of clips off and on again.

If I shift down and back up again (say from 4 to 5), no problem at all. Because of this, I'm assuming the grip shift mechanism probably needs adjusting and not the derailleur (or it would do it all the time, shifting up or down)?

Thanks!
Jason

[cyclerUK]

Somewhere on the bike will be an adjuster(s) for tightening or slacking the cable to the derailleur.
There should be one on the derailleur and maybe one on the gripshift or even on the frame.
Try adjusting this to see if that helps.
See :-
http://bikeride.com/adjust-rear-derailleur/

[erdem]

do you mean when you shift from the outermost rear sprocket (smallest sprocket) to the second sprocket near outermost rear sprocket. if this is the problem this may be related to h limit screw settings. and make sure there is no tension in the inner wire when making these adjustments.

http://www.parktool.com/repair/readhowto.asp?id=64

or practically adjust h limit screw so that the guide pulley is below the outer line of the smallest sprocket when looking from the rear.

[facelikebambi]

Thanks guys - it was a problem with the h limit screw setting and all fixed now!