Planetary Gear Set

Most conventional automatic transmissions are built from two or more planetary sets combined with clutches and brakes. Hybrid systems use planetary sets as power-split devices to blend engine and motor power. The gears are always in mesh, which makes them strong and quiet.

Holding one element, driving another and taking power from the third creates a reduction, an overdrive or reverse.

Damaged planetary gears cause whining or grinding in certain gears and often require gearbox overhaul. Low or degraded fluid accelerates wear of the bushings and thrust washers.