I had the same problem a sudden drop in pressure in my bathtub but no where else? I removed the plastic cover on the faucet which allows you to lift a retaining pin and remove the guts.I found where the ball valve opens and closes it was slicing small amounts of plastic which accumulated and cut off flow.My faucet was a Moen.

Hi RandMil and welcome to the Plumbing pageat at AskMeHelpDesk.com. You piggybacked on an a 2 year old dead thread so I gave you one of your own. In the future, before you post, look in the upper left hand corner for the date.

I found where the ball valve opens and closes it was slicing small amounts of plastic which accumulated That's before it gets to your Moen valve. Where is this ball valve? What does the plastic look like? A baggie? Something harder? More details please, Regard, Tom