How can you tell if you are using too much weight for back exercises?
If you can't hold the weight for a split second during peak contraction, you are using too much weight. Many times, you will see lifters master the ability to swing or leverage a weight up to position for DB Rows, etc., without truly gaining the strength to lift it and/or hold it without swinging it up.
When performing back exercises, concentrate on first pulling your shoulder back, then pulling your elbow back. These motions should be smooth and continuous. Lastly, concentrate on contracting your lats tightly as you finish the rep, holding the weight for a small, split second.