Subaru Forester

First-generation Subaru Foresters sold in Japan offered a 5-speed manual transmission or a 4-speed automatic transmission. So far, so typical of the cars of the time. But the Forester went further to help the driver in difficult conditions, such as ice and snow.

First of all, the manual transmission featured a viscous limited-slip differential (LSD) center differential, providing a fixed torque split of 50:50 for improved traction and stability, particularly in off-road conditions.

In case you’re wondering how and LSD helps, well it’s a type of differential that allows for some degree of torque (essentially, “twisting power”) to be transferred between wheels on the same axle. This mechanism is designed to limit the difference in wheel speed, which can be especially useful in low-traction conditions. When one wheel loses traction, the LSD can transfer more torque to the wheel with better grip, thus improving traction and stability. Think about it like this – the right rear wheel is on nice, grippy tarmac, but the left rear wheel is spinning on slippery ice, so the LSD transfers more to the wheel that has the greater amount of grip. There are many ways this can be done, such as clutch plates, helical gears, or viscous fluids.

So, what about this ‘viscous’ (not ‘vicious’!) limited-slip differential (VLSD) that you find on first generation manual Foresters? Well, this LSD uses a viscous (‘thick’) fluid to control the torque distribution between the wheels. So, what you have inside the VLSD, is a series of perforated plates connected to each axle that are immersed in a silicon-based fluid. When there’s a significant difference in wheel speed, the shear action within the fluid generates resistance, causing the plates to transfer torque from the faster-spinning wheel (the one with less traction) to the slower-spinning wheel (the one with more traction). This process helps to balance the wheel speeds and improve traction, particularly useful in conditions where one wheel may encounter less grip, such as on ice or loose gravel.

You’re probably wondering what makes the viscous limited slip differential (VLSD) you find in the manual Forester better than the other mechanical types. Well, first of all, it offers a smoother and more gradual engagement, making for a more comfortable driving experience.

You see, unlike mechanical LSDs, which use clutch plates or gears that can engage abruptly, the VLSD relies on the shear properties of viscous fluid transfers torque more gradually. So, you have a more seamless transition between ‘locked’ and ‘unlocked’ states. It’s smoother and more comfortable for you as the postal worker driver, and it helps your car handle those difficult winter conditions better as well.

Another plus is that VLSDs generally require less maintenance. The viscous fluid is sealed within the unit, reducing the need for frequent servicing compared to mechanical LSDs, which often require regular maintenance or replacement of worn parts​. Definitely a plus when you need your car available for deliveries, and you don’t want to spend your precious EMA on getting it fixed.

So, that’s the 5-speed manual transmission with it’s LSD. But, as a postal worker, you may well prefer the convenience of the automatic. Let’s have a more detailed look at the Subaru Forester SF5 and SF9 model’s automatic transmission.

Well, the automatic transmission used something called the Active Torque Split (ATS) system. It sounds impressive, but what does that actually mean? This ATS mechanism used a multi-plate transfer clutch that was electronically controlled to manage torque distribution between the front and rear wheels. The default torque split was 60% to the front wheels and 40% to the rear, which would give you good stability under regular driving conditions. But, the system was always monitoring those driving conditions and could adjust the torque distribution in real-time, redirecting torque to the wheels with the most grip to improve control on slippery or uneven surfaces. In other words, when things got slippery, it would decide which wheels had more grip, and send more of that ‘twisting power’ (torque) to them. You can see how this would be especially effective in adverse weather conditions, such as rain, snow, or ice​.

These transmission options are all part of Subaru’s Symmetrical All-Wheel Drive system. Sounds fancy, doesn’t it? But what about it is ‘symmetrical’, and why should you care?

Well, it’s because it used a symmetrical layout – horizontally opposed “boxer” engine with a symmetrical drivetrain layout – that allowed for even weight distribution along the vehicle’s centerline and created a balanced, low center of gravity. The benefit for you? Greater vehicle stability and better handling.

So, these first generation Subaru Foresters had even weight distribution, a low center of gravity, 4WD, and powertrains that would always send power to the wheels with the most grip. It’s no wonder that SF5 and SF9 Subaru Foresters have such a great reputation with postal workers who deliver in cold climate conditions.