As with the transmission, TRE completely worked over our transfer case. First everything is disassembled and hot tanked, clean enough to eat your veggies off of. A Magnaflux inspection is done on the ring and pinion gears, front differential housing and front differential gearset. Like the gearset on the transmission, there is gear detail work done to the ring and pinion to reduce stress risers and to increase strength for higher torque loads. The transfer case main and tail housings receive CNC machine work to ensure they are square to one another. The reason it is important to make certain that both housings are square to one another is because it has a profound effect on the ring and pinion contact pattern and overall durability of the transfer case. The side cover is also CNC machined for larger M10 bolts to more securely hold everything in place. The ring and pinion gear is shot peened and finished with REM Isotropic Superfinishing.
Our long-lasting Wavetrac front differential resides inside the transfer case as well. This differential has been through war and back. This was the same differential in the Evo VII when it was smashed into the wall at Road Atlanta. The transfer case was destroyed and one stub shaft became permanently attached to the Wavetrac, requiring the differential to be sent back home so the technicians at Wavetrac could separate the two parts. The differential survived with a few broken parts and was rebuilt and has continued to perform perfectly. What makes the Wavetrac special is that it works super smoothly, like an OEM Torsen differential, but with an additional locking feature if one wheel overcomes the torque bias ratio, which would normally split all the torque to the wheel with the least traction.
Back we go to the rear differential. TRE works their magic here much like the transmission and transfer case. The most important change is switching to a 12 friction disc, MAX-LOCK upgrade. Given the greater grip that the rear tires can produce, the ability for stronger locking of the rear differential is a requirement to keep proper balance of the car in on throttle situations. We go a bit against the grain by choosing a 1-way differential, which only locks on accel, not under decel or coasting situations. This allows the car to be looser under braking and initial turn-in. The car is extremely stable in general, so we didn’t feel the need to induce additional stability via the differential being set up as a 1.5 or 2-way design. As with the other gears, the ring and pinion and spider gearset are shot peened and REM Isotropic Superfinished.
Additionally, we have a TRE Heavy Duty side cover which is CNC machined from billet 4340-CR steel. This choice of steel is much tougher than the OEM cast iron, with more material in critical areas and larger corner radii making the side cover very stout. This increased rigidity eliminates deflection of the factory differential housing, keeping the ring & pinion gear running perpendicular to one another, even in the harsh environment of racing.
There you have it, all the details of the Professional Awesome Evo’s drivetrain for the world to read. Please feel free to ask any questions you migh have below!