Hey, so this is my first post on here and I do apologize if this has been asked before. I decided to purchase a shorter stem to hopefully get a better fit on my bike. I went with a relatively cheap 90mm one from amazon just to see if I'd like the fit. I just installed it and my bike seems to wobble when I engage the brakes and rock the bike back and forth. The new stem didn't come with its own top cap and the one in using from my old stem seems to not fit entirely on. Could this be the cause of the wobble? Or is it something else. I'm new to biking in general and I'd greatly appreciate any help or advice.