How can I find a replacement derailleur for a nice bike that is 20 years old (GT Winstream) My derailleur kinked up when I was pedaling hard and became a twisted mass of metal. It has a derailleur in the back which is a Shimano Altus and has some numbers on it that Google didn't identify. I can't find a manual for the exact bike online, I think it is a 2003 model.
Does anyone know how to find the exact specifications for such a derailer? I am afraid that if I go to a bike repair shop, they will tell me that they (and they alone) have the right connections to get the part and then they will order one, and I will have to pay the price for a brand new one, plus shipping and then pay the guy 45 bucks an hour to install the thing.
I could probably get another bike like mine used for what I might pay the professional. (If I were very wealthy then I would support such people as bike repairmen, but I prefer to borrow tools from friends and fix things myself.
Good news. Shimano kept broad compatibility between their products, even between generations.
An Altus derailleur from circa 2002 may be from a 7 or 8 speed (number of gears in the rear cluster) drivetrain. You can actually use any Shimano 7, 8 or 9 speed derailleur with a 7 or 8 speed shifter. Shimano used the same derailleur actuation ratio (ratio of cable pulled to lateral derailleur movement) for all these drivetrains.
Remember you need to select a derailleur that has a sufficient total capacity (capacity required is (difference between max and min sprockets teeth) + (difference between max and min chainring teeth), and has a appropriate max and min largest sprocket size for the sprockets on your cassette.