Hello Tom, thank you for your question. The washer that goes right after the coupler is part number WP2198661 and looks like a plain flat washer. I don't believe there is anything specific about it. I would recommend checking the assembly again to make sure all the spacers are in the right spot. It sounds like the coupler is slipping from the motor shaft. You might want to check the shaft and the Drive Shaft Coupling Sleeve, and Seal ( items# 26 36 30 on the bucket diagram). I hope this helps!