I am building a road bike with shimano 9 speed parts for the drivetrain. I have a shimano 105 derailleur model number RD-1050. It is a 7 speed derailleur. I have heard that the speed number of a rear derailleur doesnt matter, and that only the shifters and cassette need to match. Could I use this deraileur with an otherwise all 9 speed drivetrain? Basically, is a 7 speed derailleur really any different than a 9 speed one?
I ran a Shimano LX from the 7-spd era on a otherwise 9 spd setup until bushing play and slop caused me to retire it. Ran just fine. Given that there's some lateral play in the guide pulley anyhow, speed nomination on the RD usually isn't critical.
No guarantees though, there might still be combos out there that won't play nice together.