So I'm learning a song on my violin which is played at 100 bpm and I'm having trouble switching between two eighth notes, a C on the high E string and C on the A string. I thought I'd shift up and then just play the lower C on the D string using my pinkie so I wouldn't have to shift all the way down to first or second position on the A string. But when I'm trying switch, even when I'm going slow, it sounds really squeaky and the lower C isn't... ringing or heard all that well. To be clear, I'm trying to switch from fourth position on the high E string to the C way up on the D string swinging over my pinkie. Any suggestions would be appreciated.
To be clear, I'm trying to switch from fourth position on the high E string
In that case your first finger is on the lowest B on the E string and your second finger is on the C. The C on the A string is then one octave below that. The "correct/normal" way to play consecutive notes an octave apart is with the fourth finger on the high note and the first finger on the low note on the next lower string. To that end you need to play the first C in second position not fourth and it will become much easier. You need to arrange your shifting and fingering to play the first C in second position.
Playing this way will be much easier than crossing from E to D string without touching the A string and will sound much better. The tone quality differences between E and D strings are much greater than between E and A.