WPC can be viewed as a shot peening process that hardens the surface of a part by shooting very small particles at it at extremely high speeds. The added hardness comes from a process similar to work hardening. Work hardening happens in most metals like when a paper clip is bent back and forth repeatedly until it breaks. Every time the wire is bent and unbent, small discontinuities in the wire's crystalline structure form. These discontinuities increase the hardness of a part until it gets so hard and now brittle it finally breaks.
But because this is only a surface treatment, the hardness does not affect the overall strength of our gears, which we addressed with the deep cryonics. The difference of WPC from conventional shot peening is the size of the shots and the speed that it's shot at. The shot media are so small that they can't really even be called shots. By shooting the WPC media at a part, the impact energy essentially compacts and deforms the lattice structure of a metal surface at a molecular level. The surface is essentially work hardened, but without the large dents left by standard larger shots. This means that WPC can even be used on machined surfaces with negligible dimensional changes (less than a ten-thousandth of an inch in soft materials). Another advantage of the WPC process is the micro divots left in the surface. Each little divot left from a shot impact now acts as an oil reservoir for lubrication to sit in and hold onto. This is perfect for gear faces, syncros, and even wet clutch plates found in LSDs to help eliminate noise.
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Performance Autosports Service & Supplies supplied the TRD pinion collars. The stock unit,
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KAAZ USA performed the final assembly of our rear axle. The pinion, collar, seals, and bea
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After everything is adjusted and tightened, marker grease is applied between the ring and
The Rear Axle
With all the gears, bearings and seals flying about, we decided to give Project Corolla's rear axle and differential the same treatment, as Corolla rear ends are notoriously weak. So the entire axle was removed, cleaned of rust, hot tanked to remove the idiotic metallic blue spray paint the previous owner had an affinity for, and finally powder coated in a satin black. Internally, the axles were removed for inspection and trued on a lathe, while the worn stock GTS limited-slip differential was dumped in favor of a TRD 2-way clutch-type LSD. We also purchased a new stock ratio ring and pinion to be sent out for cryo and WPC. Although TRD offers a 4.778:1 ratio final drive that would immensely help acceleration and engine response, we stuck with the lower stock 4.3:1 since the car would have to be driven to the track.
We ultimately decided on the TRD LSD because it was designed with track performance in mind. Because the Corolla uses such a small differential, the overall diameter of the clutch plates inside the diff housing are limited to just a few inches. Smaller diameter clutch plates mean less surface area and less torque moment to keep the wheels locked. To compensate, TRD designed the unit with a significant amount of preload to get the clutch plates to engage and lock as fast as possible. While we don't typically like a diff that locks fast and has limited holding power, the TRD unit actually works out in our favor since the huge grip generated by our Nitto NT-01 tires is enough to overcome much of the initial lock of the diff, which typically contributes to mild on throttle understeer. The 2-way locking action also helps the car rotate better under lift throttle. So everything balances out with some tire and driving style adjustments.
Just like with the transmission, a rebuild kit for the rear axle was ordered up from Max Misawa of Illegal Garage. We also added a TRD solid pinion collar sourced from Performance Autosports Service & Supplies in Industry, California to prevent our new pinion from moving around too much. Installation of the new diff, ring, and pinion was handled by Ray Nakadate, President of KAAZ USA and long time Corolla fanatic.