I am in the process of rehabbing an old Mongoose mountain bike from 1984. In the course of the tear down cleaning etc. I noticed that the upper pulley is smaller than the lower pulley. It does not look overly worn. Is this normal for this RD? I am sorry i don't have any pictures as the camera is down at the moment.
I just looked at my Mountech (Bought in 1983-4) and, as I removed the lower pulley, compared the upper with another lower. Several others actually. And yes - the upper wheel is notably smaller than most wheels. If the upper wheel is still attached, it contains a spring which gave it awesome shifting powers. It was in competition with the Huret Duopar. Removing the upper wheel would be stupid - it's what made it shift as well as they did/do. Looking from the front (as though towards the freewheel/cassette), is there on silver hex-nut in the center of the upper wheel? Is this surrounded by what looks like a silver washer? Surrounding this should be a gray-colored plastic "washer." Then a much thinner black-plastic washer. Then you have the derailleur cage itself.
This wheel was what made it work so very well. It's also the part that was blowing apart. The inner spring would escape with some velocity - causing crashes and injuries. That was the end of the Mountech. And Suntour itself vanished a few years later.
Ride on it at your own risk. I took mine off the bike it was on. I'm keeping it as a curio.
Does this match what you have?
Originally Posted by Cateye
Only panthers007 is stupid enough to believe that this is a good idea.