1. Orientation and packaging: A FWD transmission is designed to be mounted *transversely* (across the engine bay, perpendicular to the vehicle's longitudinal axis). This necessitates a compact, often integrated design with the differential built-in to minimize overall width. A rear-engine transmission, conversely, is typically mounted *longitudinally* (along the vehicle's longitudinal axis), often allowing for a more separated and potentially larger design. The packaging constraints are drastically different.
2. Drive shaft configuration: FWD transmissions drive the front wheels directly through short half-shafts. Rear-engine vehicles might use a driveshaft running the length of the car to the rear axle (for rear-wheel drive), requiring a different output flange and potentially a different type of final drive. In some rear engine layouts, particularly in compact cars, a shorter driveshaft may be used. The key is the *absence* of a long driveshaft in the FWD configuration.
