Mark VIII Driveshaft Swap



The factory EEC limits the top speed of the Thunderbird to about 105 mph, and a chip or re-flash is required to remove the govorner. Altho the speedometer only goes up to 120 mph, 145+ mph is possible. The SuperCoupe speedometer directly swaps into the gauge cluster, and will accurately display these higher speeds. The factory steel driveshaft becomes unsafe above 120 mph, and a new driveshaft is required to obtain higher speeds. Most Lincoln Mark VIII Driveshafts are made of aluminum, and are two piece units. Only the 1993 Mark VIII came with a one piece driveshaft, and is the preferred shaft of choice.



The first thing to remove is the exhaust. On my Thunderbird, the custom dual exhaust is all one piece, so the entire assembly was taken down. Most other Thunderbirds, would only require the exhaust to be removed after the catalytic converter, or resonator, depending on the year and model.


Here the car is shown supported by jack stands, and ramps. Once the exhaust is is removed the gas tank will be dropped. Make sure your gas tank is empty, or nearly empty before attempting to remove the tank. Use a jack to hold the tank up while unbolting the two retaining straps holding the tank to the underside of the vehicle. The fuel filler neck, and lines are taken off, and I have stuffed them with a rag to keep gasoline vapors to a minimum.


Now the factory driveshaft may be unbolted, only 4 bolts hold the shaft to the differential. Altho the bolts look akward, they are normal bolts and 12 point sockets should be used. Notice the yellow alignment dots painted on both the shaft and rear axle universal joint flange. When the bolts are removed, the shaft may be lowered, and pulled out of the transmission.


Here are the two driveshafts side by side. The aluminum Mark VIII driveshaft weighs 14 pounds, and the steel shaft 19 pounds. Less arbitrary weight on the driveline.


These pictures show the transmission and rear end without the driveshaft installed. When installing the Mark VIII shaft, make sure the yellow paint marks line up.


After installation, the bolts should be torqued to factory specs ( 71-95 lb-ft ). Then using the jack, lift and re-install the gas tank, and exhaust assembly. Always wear your seat belt when driving 145+ mph =)


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