A seed meter for a planting machine is provided with an adjustable drive coupling between the seed meter and the planting machine main drive. The drive coupling includes a drive member connected to the planter drive and a driven member coupled to the seed meter shaft. The drive member and driven member are drivingly engagable with one another and held into the engaged position by a biasing member. The drive member and driven member are selectively movable relative to one another to a disengaged position, enabling adjustment of the seed meter relative to the drive by rotation of the meter shaft. Once released, the coupling self-engages.