In a large bowl mix together, the mayonnaise, sour cream, ranch dressing mix, dill weed, celery seed, plus the 1/4 teaspoon and 1/8 teaspoon of black pepper.
Add the sliced cucumbers and onion, and gently stir to mix everything together.
Serve salad immediately.
Note: I have made this salad twice, once using chopped white onion, and thinly sliced green onion. The second time I made this salad, I added 4 tablespoons of finely chopped red onion, in place of the white and green onion, and that tasted great in the salad too! Also, when I added the sliced cucumbers, they were cucumbers I had in the refrigerator, which help the salad to stay cool.