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2004 Mustang Cobra Wheelhop Fix - IRS Fore-Play
Fore Precision Works And Maximum Motorsports Help Us Eliminate Wheelhop.
To install both pieces, we took a trip to Bohemia, New York, and visited Realspeed Automotive where Dan Carlson had a Cobra needing a fix for the dreaded wheelhop. Bill Loper's silver '04 Cobra arrived sporting a Whipple twin-screw and Snow alcohol injection. It laid down a street-friendly 568 rwhp on Realspeed's Mustang dynamometer. When Loper heads to the track, his Snake is treated to a little race gas and added boost, bringing the rwhp number to 640. With a Spec Stage III clutch, aftermarket halfshafts, and Nitto drag radials, wheelhop is still an issue and it was time to put an end to it.
The first step in the process was removing all of the parts that would be in the way. To change the rear mount and differential cover, we needed to remove the center section from the car. Once the exhaust and axles were removed, Rob DeMartinis made quick work of getting the differential out.
At the time of our installation, neither the Fore or Maximum piece were designed to work with each other, but we had a fix. In addition, the Fore cover we had was a prototype unit. In order accommodate both pieces and maximize the strength potential of the IRS, Carlson sent the Maximum Motorsports rear mount to Fore Precision Works where Fore machined the needed changes to make it compatible.
Although the Maximum mount was modified, we still needed to remove some material from the new cover to accommodate the mount. With the cover swapped and the billet mount secured in place, the process of test fitting the differential began. As soon as the center section was in place, it was clear some trimming was in order. With the center section bolted in, DeMartinis marked both the cover and the bracket for the driver's side tie rod, which needed to be modified for clearance. Production pieces are designed to bolt right into place. After Carlson removed a small amount of aluminum from the differential cover and trimmed the tie-rod bracket, the center section went right in.
With a pole jack supporting the pinion, DeMartinis test fit the spherical washers for the front mount. These washers help locate the front of the center section and put no bending force on the front mounting ears of the differential. They also allow you to raise or lower the pinion angle, which helps eliminate vibrations in the driveline. Once the washers were loosely in place, DeMartinis used an angle finder to set the pinion angle at 31/2 degrees positive (remember the pinion doesn't move). After the rest of the rear end was reassembled and the exhaust was reinstalled, Carlson took the Cobra for a spirited test drive.
The solid mounds add a slight more noise than the stock rubber bushings, but the rear felt solid under the car and wheelhop was reduced dramatically. Now with our differential solidly mounted in the car, we're ready to pour more power to the pavement without worrying about wheelhop.