Slips/Chatters In Manual 1st Gear
WARNING: This page does not describe the selected car, but rather 13 other vehicles, including the 2003 Mazda B4000, 2003 Mazda B3000, 2003 Mazda B2300, 2002 Mazda B4000, and 2002 Mazda B3000. However, it is still accessible from the selected car via links, so may be relevant.
Check the following: high or low line pressure, valve body (sticking valves or damaged separator plate or gasket), or rear one-way clutch damaged.