The bell housing is part of the transmission system on a petrol or diesel powered vehicle. It is bolted to the engine block and contains the flywheel, the torque converter or clutch of the transmission. The starter motor is usually mounted here engaging with a ring gear on the flywheel. On the opposite end to the engine is usually bolted the gearbox.

The above is the normal arrangement for an in line transmission system for a conventional rear wheel drive or all wheel drive vehicle. The arrangement for a transverse mounted engine and transmission for a front wheel drive vehicle has the gear box and differential below the engine and consequently the bell housing is a simple cover for the flywheel.