Cusco 1.5-Way Rear Diff

Tight autocross elements kept exposing the same weakness. In the tightest turns, the inside rear wheel would lift, the stock rear diff would send the power straight to it, and the car would just sit there spinning instead of driving out of the corner.

The fix was a Cusco Type-RS 1.5-way limited slip. Inside are clutch packs and springs that tie the rear wheels together under power, and partly under deceleration.

I did the swap myself on the bench. Out came the old diff, the ring gear moved over to the Cusco case, and the bolts got torqued and paint-marked.

Then I checked the setup: gear marking compound for the contact pattern, and a dial indicator for backlash. I filled it with Motul 75W-90 LSD gear oil, the friction-modified oil a clutch-type diff like the Cusco needs.

It took a bit of relearning. Coming off a corner, the rear can step out under power much more easily than before, so I had to be smoother with the throttle. Once I adapted, I really loved it. It puts the power down where the old diff couldn't, and the partial lockup on deceleration helps rotate the car a little on entry.