
Converting a car that was originally designed as front-wheel drive (FWD) or rear-wheel drive (RWD) into an all-wheel drive (AWD) vehicle is technically possible, but it is an extremely complex, time-consuming, and expensive process that is rarely practical or cost-effective. For the vast majority of car owners, it is not a feasible DIY project and requires specialized engineering expertise. The most sensible path to gaining AWD is to purchase a vehicle that was designed and manufactured with an AWD system from the factory.
The primary challenge lies in the integration of entirely new components that your car was not built to accommodate. A proper AWD conversion involves installing a transfer case (which distributes power to both axles), a new transmission or extensive modifications to the existing one, a rear differential (for a FWD car) or a front differential (for a RWD car), and a pair of driveshafts to connect everything. This also necessitates fabricating custom mounting points for these components, which often involves cutting and welding the vehicle's chassis or subframe.
Beyond the major drivetrain components, you must also consider the supporting systems. The suspension will need significant recalibration or replacement to handle the new weight distribution and driving dynamics. The braking system may need an upgrade to manage the increased performance and weight. Furthermore, the vehicle's computer (ECU) is programmed for a 2WD setup and will require extensive reprogramming or replacement to properly manage an AWD system.
The financial aspect is the ultimate deterrent. The cost of parts alone for a proper conversion can easily exceed $10,000 to $20,000, not including the hundreds of hours of skilled labor. This investment almost always far surpasses the value of the car itself and the price difference between a 2WD model and its factory AWD counterpart. You are essentially undertaking a project that replicates the R&D work of an entire automotive manufacturer.

As a mechanic, I've seen people ask about this. Honestly, it's a nightmare. You're not just bolting on a part; you're re-engineering the car. You need a new transmission, driveshafts, a rear differential, and a way to make it all fit a chassis that wasn't designed for it. The labor and custom fabrication costs would be astronomical. You'd be better off trading your car in for one that's AWD from the factory. It'll be cheaper and way more reliable.