Originally Posted by
Bob Ross
I've long contended that if you don't know how to remove the "plastic thing" without destroying it, you should leave it on...but I realize that's a pretty snarky attitude.
More importantly, it sounds like you (OP) need to leave it on, at least until you've had a chance to take your bike to an experienced mechanic for a rear derailleur adjustment, because right now that plastic thing is doing its job.
None of my Road wheels have ever had them on except that a set of Mavic wheels I bought had one supplied in the box. I fitted in and then found the Cassette would not locate properly. MTB's and I left them on the wheels till I made certain that the RD was adjusted properly and then next cassette removal and I took it off.
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How long was I in the army? Five foot seven.
Spike Milligan