Bicycle Mechanics - Repeated broken Derailleur- Please Help!

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nfoolchand
01-01-10, 06:00 AM
A happy new year to all,

i wish i could continue on the festive cheer but i have a repeated problem with my derailleur and would love someone with more knowledge to have some input.

When changing gear one day i noticed there was a problem with my derailleur.......the fact was the upper of the two cogs just wasnt there! The cog had completely dropped off the bike whist shifting! In my disappointed state i went to a repair shop (which i have to admit uses second hand parts) to fix it and the problem seemed fine but alas, after about 15 miles, the very same thing happened.

I understand that its is very difficult to diagnose such a problem when not with the bike, but i am wondering if anyone knows of any common problems which may put undue pressure on this part which then causes it to disintegrate!

Is it time for a new bike you think? Or are such things repairable without changing the derailleur, free wheel, chain etc.

Any advice would be appreciated.

Thanks

Retro Grouch
01-01-10, 06:12 AM
If I had to guess I'd say somehow the cage was damaged and the little bolt that holds in the upper jockey pulley keeps coming out. If it was my bike, I'd replace the whole rear derailleur. A used rear derailleur is usually an OK bet provided it has adequate capacities. Rear derailleurs usually take a long time to wear out.
Steev
01-01-10, 06:18 AM
Maybe the "B" limit screw is missing and the jockey wheel is mashing into the larger cogs.

nfoolchand
01-01-10, 06:30 AM
No, i am pretty sure the jockey wheel wasnt moving onto the cogs. I did notice there was maybe more 'play' in the jockey wheel previously so maybe the first person who replied might be correct in saying the cage was damaged!

Thanks guys.

PS: Keep the ideas coming!
Bianchigirll
01-01-10, 06:55 AM
go to a good shop and have a new rear derailleur put on. it is possible since you have lost atleast two upper pulleys the threading is worn or stripped. since a common way to install a new rear derailleur (without a new chain) is to remove one of the pulleys, normally (atleast for me) the upper one. just politely ask them to ensure the bolt is tight and perhaps a dash of loctite. modern front derailleurs are very accurate devices and the days grabbing a used shimano lower pulley and making it work on the top are long gone.