Toyota & Lexus 4WD Drivetrain Technologies: Here’s How They Work
Toyota & Lexus 4WD drivetrain technologies provide improved traction in slippery conditions, but they also vary in terms of operation.
In essence, pretty much all four-wheel-drive (4WD) systems accomplish the same sort of thing – they all use some form of powertrain and drivetrain setup to move all four wheels on a vehicle, rather than just the front or rear independently. The benefits are obvious, too – increased traction in all conditions, whether that be slippery snow and ice on the roadways or while navigating various off-road obstacles. However, these systems otherwise tend to function a little differently, and that includes Toyota & Lexus 4WD drivetrain technologies.
For the purposes of today’s article, we’re going to focus on larger, body-on-frame truck and SUV 4WD technologies, as the companies’ crossover-based vehicles have a different architecture and layout.
Toyota & Lexus 4WD systems have developed a strong reputation over the years for being quite capable on these types of terrains, with a lot of off-road racing success under the automaker’s belt for that very same reason. This tech has trickled down to road-going vehicles as well, which is obviously great news for consumers. In essence, Toyota 4WD systems are offered in two configurations:
part-time and full-time
Body-on-frame Toyota and Lexus models utilize a front-engine, rear-wheel-drive layout by default, which is great for regular driving conditions – and aided by a limited-slip rear differential in some cases. In those same vehicles that offer part-time AWD, the system can be switched on and off as needed, distributing power between all four wheels in lower-traction conditions. The benefit here is that only using the rear wheels results in greater efficiency, but one can also opt for 4WD when needed.
When activated, part-time 4WD locks the front and rear axles together with a transfer case, which uses a planetary gearset to divide the power evenly between two driveshafts connected by a heavy-duty chain. As a result, the front and rear wheels turn at the same speed, but the transfer case also has two settings – 4H (four-high), and 4L (four-low). 4H sends power straight to the drive wheels for great grip when driving through slippery conditions.
As for 4L, it’s more intended for slow-speed conditions that require extra torque, such as when crawling over rocks, as 4L multiplies torque with its low-range gear and provides additional engine braking to the wheels. 4L also gets Active Traction Control (A-TRAC) – which detects traction loss and applies the brakes to individual wheels that don’t have traction – and a locking rear differential on select models, the latter of which ensures that the rear wheels are receiving equal power, regardless of terrain.
However, part-time Toyota 4WD systems should only be used on slippery surfaces, due to the fact that on dry pavement, it causes the wheels to intermittently bind when turning, as the front and rear axles are being driven at the same speed and can’t rotate independently when going around a curve, which forces the wheels to slip instead.
Full-time Toyota & Lexus 4WD systems, which you’ll find on the current GX 550 models, don’t have that problem, and operate at all times, regardless of traction conditions. It’s quite similar to a part-time system, but instead of a transfer case, it utilizes a Torsen case or Torque-Sensing center differential to distribute power and allow the wheels to turn independently. This system reacts to traction loss between the front and rear axles by reducing the slippage between them, eliminating the binding issue. The center diff also includes a locking function for maximum traction, improving control further.
Join the Club Lexus forums now!
