TRANSMISSION
The RS’s 4WD system uses a Getrag MMT6 gearbox, which is durable even at higher power and when used hard. A set of shot-peened gears adds peace of mind for those running silly power and regularly abusing it on track, but if your RS isn’t an Edition model, then the first upgrade here should be to fit a limited-slip differential – it makes such a difference to the way car drives both on track and road.
The Quaife ATB is the most popular and is what Ford fitted at the factory, but another option is the Wavetrac unit available through specialists like Steeda.
The rear differential unit houses the clever electricallycontrolled clutch packs. It looks puny compared to rear axles of old, but you’ll struggle to break one. Mind you, that’s mainly because the clever computers prevent too much torque being delivered to it, and when it gets hot the ECU shuts it down and reverts to FWD spec. Diff cooler plates that direct cooling air across the differential are available, but given the rear diff (RDU, Rear Drive Unit in Ford speak) doesn’t actually have a temperature sensor – instead, the RDU is closely linked with the car’s ECU and infers a temperature based on a calculation of wheel speed, throttle position, and gearbox/PTU oil temperature – some will question their effectiveness.
That’s not to say tuners haven’t investigated the issue further; Mishimoto has a detailed blog on researching and developing a cooler kit that relocates the PTU temperature sensor to bring the inferred calculation back below the critical RDU shutdown point, but at the time of writing we aren’t aware of any complete diff cooler kits currently on the market. That said, as more and more owners venture on track, we don’t think it will be too long before we do.
One thing that is a no-brainer, though, is a decent quickshift kit. They make a huge difference to the feel of the car every single time you drive it; just make sure you choose a shifter with some weight in it to ensure a smooth, positive shift.