5.0 Mustang & Super FordsHow To Drivetrain
Limited Slip Differential - Grip And Gears
Getting The Gearing And Limited Slip Correct For What's Coming Up In Our Open-Track GT
Mustang street enthusiasts like to debate which supercharger is best, drag racers are keen on internal engine parts, and road racers-strangely enough-seem fixated on limited-slip differentials. That's because an open differential spins the inside rear tire on corner exit to the point of hopelessness, while a completely locked differential promotes tire and time-scrubbing understeer. A limited-slip differential that splits the difference is best from a power and handling standpoint, but often the trick is finding one that works that you can afford.
Followers of our '96 GT open-track machine know it's aimed at serious road-course handling, which means having some sort of limited slip on hand. As the car's suspension was being heavily modified by Maximum Motorsports with its full line of handling tricks, the 8.8-inch axle in our project car remained illed with a drag/off-road-oriented Powertrax limited slip and 4.10 gears. These are great devices, but are not optimized for the open tracking we have in mind for our hot-to-trot g-machine.
The Powertrax provides the elusive and desirable lockup of the rear axle that positively provides drive to both rear tires. It's a godsend on the dragstrip, but its built-in system of ramped teeth angles means it unlocks and locks up again in midcorner if the throttle is adjusted in midcorner. At street speeds, this is no big deal-resulting in little more than a cluck and a wiggle when negotiating 90-degree intersections. At road-racing track speeds, however, the lock/unlock accompanying throttle movement can upset the car just when you've got it hung out on the edges of its tires. As we've proven ourselves fully capable of high-speed spins through the high-desert chaparral on our own, we figured we might as well avoid any mechanical help in that direction.
While there are numerous differentials to choose from in selecting a road course-compatible diff, this time around we selected the good, old Traction-Lok. Yes, the same limited-slip Ford fits optionally to Mustangs on the assembly line. There were a few good reasons to go with the Traction-Lok, not the least being availability and price. It also does its job quietly.
As does the T5 transmission in Fox chassis cars, the Traction-Lok has a divided reputation. Some folks say it quickly starts slipping and doesn't offer sufficient lockup; others are fairly happy with it. Our experience has shown that tire-smoking throttle-jockeying is the main Traction-Lok killer. Prowl the streets with burnout intent and a Traction-Lok is not going to last. Rely on it to provide protection against time-robbing wheelspin from your smooth driving on a road course, and they work fine. As with any clutch-equipped device, it's clutch slippage, and hence heat, that is the Traction-Lok enemy.