Bicycle Mechanics - Incompatible derailler?
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I have been having problems with my front derailler. the chain keeps rubbing and it wont change in and out of gears smoothly. After struggling with this problem for quite some time, i took it to my local bike shop, where i was told that derailler had come the end of its useful life and i should replace it. So they took off my old Diore derailler and tryed to change it with a new Diore LX. however the new diore LX derailler wouldnt fit and in the end my they put the old broken one back on my bike. They told me that the diore LX derailler was incompatible with my bike and because the bike was so old i wouldn't be able to find a new one that would fit. I'm not sure exactly how old my bike it, as i bought it second hand, but it has a biopace chainring, so i am guessing the it was made in the 80s. Does anyone know why new deraillers would be incompatible with my bike? is it because of the biopace chainring?
08-15-06, 05:23 AM
Seatpost clamp size, up-pull vs. down-pull, top swung vs. bottom swing, cage arc diameter, cage width. They pretty much all have to match. Older mountain bikes tended to have larger chainrings and front derailleur cages had larger arc diameters to match. The bio-pace chainrings make that issue a little trickier to solve. Nine-speed front derailleurs have a slightly narrower cage width and probably won't work quite as well with your wider chain.
All that said, if you really need a new front derailleur, I'm thinking that a Tourney TZ31 might meet all of your needs. I've got to tell you though that actually wearing out a front derailleur is pretty rare.
08-15-06, 05:53 AM
Do you still have the original front derailleur?
I gave my sister my Miyata 615 which is all original. It has biopace chainrings and a 6 speed cassette or freewheel. The front derailleur does not set up like the front derailleur on any other bike I've worked on. It's possible, although unlikely, that the grey-haired mechanic had a day off the day you took your bike to the LBS, and the high school junior summer mechanic worked on your bike. The front derailleur sits very high over these chain rings and for some inexplicable reason the stops are further inboard and outboard than I'm used to seeing. It looks as though the chain would fly off in both directions, but it doesn't. I can only suggest that you confirm that the LBS mechanic is familiar with this set-up, circa '86. Unless the chain has actually worn through the metal cage of your front d., like Retro, I can't imagine that it's worn out. It may just need a careful cleaning and lube. (Thin lube is not recommended for certain parts of a derailleur, so get some servicing information before you start). This is likely a rugged touring derailleur good for thousands of miles. Good luck. I'll be curious how you make out. :D
Thanks for the advice, what exactly is invloved in cleaning and lubing the front derailler? I can't really see how you would get into it. I was told by the mechanic at the LBS that it was the spring that had worn out in the front derailler, i don't know if this is possible, but i have toured for several thousand km on this bike as well as unknown milage from the previous owner (although i suspect that they didnt use the bike much), so if it is possible they wear out i wouldnt be surprised. I have noticed that the derailler moves forwards and backwards as well as in and out from the bike, is it supposed to do this?
08-15-06, 01:50 PM
The derailleur should not have the lateral play that you're descibing. It doesn't sound good. I don't know if and LX is a suitable replacement. You can try a post with the model # of the old derailleur. There is the Tourney that Retro mentioned as a possible replacement; maybe someone else will have another suggestion if they know exactly what derailleur you have. Sorry that I'm not much help.
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