Low shower Pressure???

[Tom M.]

I have a fifteen year old Delta shower, it's a single lever that turns counter-clockwise. (It appears to be a 1300 or 1400.)The water pressure recently loss pressure. It is extremely low coming out of the lower faucet, not just the head. Why the sudden drop in pressure?

[Terry]

If it's the pressure balance faucet, then any blockage from either side would reduce the entire pressure.

Removing the cartridge and inspecting may be in order.