Here's are a couple of great article's on the PTU,RDU on the PI which is similar to the SHO with the exception of the 3:39 Gear ratio IIRC on the PI! Z
The Power Transfer Unit uses an internal temperature sensor, not found on the retail unit. A module keeps track of oil temperature in the PTU and the amount of time spent at that temperature. An electric clutch pack engages and disengages as torque is transferred to the rear wheels.
Third, the Rear Differential Unit on the police version uses a fluid-filled clutch pack, while the retail version uses dry clutches. The fluid-filled RDU can withstand more severe duty.The cooling ability of the police-only auxiliary radiator-water jacket combination was tested in 110 deg. F weather. Hard driving—where power is constantly shifting from front to rear, back and forth—can take many different forms.
Under the worst conditions of high-torque, clutch engagement and disengagement, the synthetic oil reached temperatures around 195 deg F. The special lube is rated for temps just over 500 deg F. The air-to-water cooler works.
Ford Tough AWD in Police Interceptorhttp://www.hendonpub.com/resources/article_archive/results/details?id=5091http://www.hendonpub.com/resources/article_archive/results/details?id=4650