I too have Avid Shorty 4 brakes. Sounds like you toed them too much. These brakes only need a slight bit of toeing.
Also, did you wipe the rims with a degreaser or solvent? That will also cause the problem you described.
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The Lord is merciful and gracious, slow to anger and abounding in steadfast love. - Psalm 103:8
I am a cyclist. I am not the fastest or the fittest. But I will get to where I'm going with a smile on my face.