We tune and tweak, we bore and stroke, and if we're serious, we even blow and squeeze, but there's still only one bottom line: Unless we get the power to pavement, it's all for naught. Tire and suspension choices play their parts, but so does the differential--the gearing apparatus that transmits the power from the driveshaft to the drive axles, while also allowing the outside wheel to turn faster than the inside wheel during a turn. There are a multitude of differentials, from standard "open" types to limited-slip and Posi-traction units and spools, which lock the axles together for maximum straight-line performance, and plenty of others. While the diff cover was off our guinea-pig '65 Malibu SS for our "Drumming Away" big drum upgrade (Jul.'04), the car's owner, Johnny Harrigan, decided to install his weapon of choice: Richmond Gear's Powertrax
No-Slip Traction System. We were on the scene with camera in hand to snag the story.One unique feature of the Powertrax unit is that it is installed inside the vehicle's existing differential case; this proved to be a straightforward process. Once installed, Powertrax claims that the No-Slip Traction System provides superior power distribution compared to open and limited-slip differentials. The latter two, according to the manufacturer, direct all (open) or most (limited-slip) of the engine's power to the slipping wheel during a loss-of-traction situation. The Powertrax, according to its maker, delivers traction to the non-slipping wheel for maximum traction. The result, according to Powertrax, is that the "No-Slip Traction System automatically distributes engine power to the drive wheels for maximum traction output while allowing full differentiation for turning." So, with our exploded lead view of the Powertrax for reference, and paraphrasing freely from the owner's manual (which can be downloaded from the Powertrax Web site), we'll explain how this particular diff unit works.
As with an open differential, the pinion gear carries engine power to the ring gear, which is attached to the differential case. The rotating differential case transfers the power to the axle shafts through the components within the differential case, starting with the drivers, which eliminate the spider gears. Both drivers are connected to mating couplers, which join onto the axle shaft splines and replace the side gears. Saddle springs inserted into the driver saddles press upon a new high-strength pinion shaft, pressing the drivers outward onto the couplers. Active spacers fit within the drivers and onto the couplers, communicating the pinion shaft position to the synchro ring mechanisms within the couplers.
The saddle springs center the driver saddles on the pinion shaft and provide damping as power is applied. As the differential case rotates, the pinion shaft advances with it, compressing the saddle springs until the pinion shaft contacts the driver's saddles at a positive-power transfer angle. Power is then directed from the drivers to the couplers through positive engagement tooth profiles on the driver and coupler faces, which mesh to transfer full power to the drive wheels. When the vehicle is driven straight, all the power is delivered to both wheels through both sets of drivers and couplers.
In a turn, the outside wheel effectively "accelerates" ahead of the inside wheel to compensate for the difference in turning radius distance versus the outer wheels. As the outer wheel rotates faster to travel farther than the inner wheel, it advances the coupler from the driver and relaxes the power distributed to the outside wheel. As the coupler continues to advance, it ramps the driver to disengage from the coupler. The synchro ring continues to turn with the coupler until the active spacer paddle stops it. The synchro ring is then positioned to prevent re-engagement of the driver and coupler until the turn is complete. The outside wheel continues to rotate freely, with power being delivered to the inside wheel. When turning concludes, the synchro mechanism is reset and power is reapplied to both driving wheels. Full wheel differentiation is thereby provided automatically and identically for right and left turns. Whew!
Yes, yes, you say, but how does it work? We thought ahead enough to test acceleration before installation with our trusty Escort Passport GT2 Vehicle Performance Computer, and headed back for a retry after a half-day installation and 50 miles of break-in time. Here's what we got:
Nice improvements, to be sure, and even better because we weren't trying all that hard. With the stock open diff in place and launching at a mild 1,500 rpm, wheelspin was rampant all the way until Second gear kicked in. With the Powertrax in place and launching at the same rpm, there was nary a tire chirp, and nothing even remotely resembling tire spin--the ol' Mali just hooked and booked. This is evident from the numbers: 0.22 off our 60-foot time, and more than a second off our 0- to 60-mph time. Had we not been using a public (albeit empty) street, we're certain more aggressive launches would have yielded even better times. Nonetheless, the improvement was marked.
As for drivability issues, Harrigan has noted only one: as noted in the owner's manual, the inside wheel "chirps" under acceleration from a stop into a turn as the inside wheel tries to catch up to the faster-spinning outside wheel. In other turn situations, this hasn't been a problem. Other possibilities that are mentioned: driveline backlash and accentuated understeer, have not been issues with our '65 SS Mali. In this case, we can say this: Powertrax's No-Slip Traction system was exceptionally easy to install, gave us a substantial performance improvement, and has shown no drawbacks so far. Follow along, and we'll show you how easily the no-slip system slips in.