This past summer the front derailleur on my mountain bike broke. When I purchased my bike I was looking for something affordable with a good frame. The frame was the most important consideration because the rest could be replaced as more money became available. Cost being an important aspect of every purchase and repair I chose to do all the work myself, so to that end I picked up a book on bicycle maintenance and repair and read the section about front derailleurs several times, truth be know several is really not the right word. I thought I understood what type of bracket was used on my bike, an E-ring which requires a special bolt on location. After the part arrive I had a friend, with the proper tools, help me take the old one off only to discover that no such bolt on connection existed and returning the derailleur for another one with the appropriate bracket type, a clamp on, was my only option. Fortunately the company I order the part from, Excel Sports Boulder, only charged me shipping.
Move ahead one week, the new part arrived and my friend and I got the derailleur onto the bike, oh happy day. But the next problem presented itself, the new derailleur required a thinner chain than the current one. Can you imagine that, I never knew chains came in different widths before. Back to the internet I went and this time through Amazon, I purchased a thinner chain, again it took about one week to arrive, I am cheap when it comes to shipping costs. Now it should be simple enough to change out the chain, right, I wish that had been so. First thing to happened was I broke my chain brake tool while shortening the new chain to match the old one, and had to purchase another at a local variety store. I finally got my chain to the right length fed it through the system and put in the pin, now I am done, right? Boy couldn't be more wrong, I fed the chain over the top of a tab between the two small wheel at the rear derailleur. Arrrrggggg!!!!! This time I went to REI and purchased a couple of extra pins, just in case, and restrung my chain put in the new pin. Since it is now snowing it will be spring before I discover for sure if everything was done correctly.
I suppose the lesson here is to do a bit more research and pay closer attention to how parts were put together before removing them so that the process can be duplicated properly.