Missliz--Get more members/class participants to "complain". The instructors can only be involved up to a certain point, because the management will use the instuctor as a scape goat if the instructor gets too vocal/sides with clients.

You can also "take the manager by the hand", walk them over to a spin bike and show them the problem. Then, you can emphasis how an injury can happen (and he/she better pray it isn't you!).
Then, if he/she doesn't listen, I'd go over their head and not worry about alienating anyone. They have an obligation and are held to a higher standard of knowledge and I bet their insurance company doesn't know they aren't maintaining the spin bikes...

You can say all of this sort of stuff in a very nice way, but you need to get your point across. You can also suggest that management check on the guy doing repairs...they may be getting ripped off and might not know it.

Moral support seems low on the priority list in most gyms...poor management always pegs a few members as "complainers" to their bosses, but, being a savvy woman, you can win the hearts and minds of the upper management people. It works every time.
Terry