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Powertrax No-Slip Traction System - Power To The Pavement

Not Taking A Spin With Powertrax's No-Slip Traction System

John Nelson Sep 26, 2005

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.


From the "while it was apart" department: Before installing his Powertrax unit, our Malibu SS owner decided to add a bearing cap stud kit from Summit Racing. This is an easy one: The stock cap bolts are removed, the new studs are screwed in to 10 lb-ft with an Allen wrench, and then the cap nuts are torqued to 60-70 lb-ft--all done using plenty of the supplied assembly lube.

From the "while it was apart" department: Before installing his Powertrax unit, our Malibu SS owner decided to add a bearing cap stud kit from Summit Racing. This is an easy one: The stock cap bolts are removed, the new studs are screwed in to 10 lb-ft with an Allen wrench, and then the cap nuts are torqued to 60-70 lb-ft--all done using plenty of the supplied assembly lube.

This, then, is where we start--with an empty differential case, held securely in place with our new bearing cap stud kit. The 3.55:1 gearset hasn't been disturbed. Time to move on to the Powertrax installation. Be sure to refer to our exploded-view lead for the overall scoop.

Normally, we strongly recommend that you follow the manufacturer's instructions when installing any aftermarket piece. In this case, our man Harrigan had a pretty cool variation that we think worked pretty well. He started by assembling the unit on the bench. This is the ring gear-side coupler (left) and driver. Note that the spacer paddle (arrow) was properly inserted into the driver, and the paddle opening in the synchro ring was positioned so the two pieces could be properly mated.

The non-slotted coupler (non-ring gear-side) goes together in a similar fashion, and the two sides now face each other, ready to be temporarily mated. One thing to especially remember here, while actually installing the unit into the diff case, the slotted driver's spacer paddle will face out towards you; the opposite side will face 180 degrees away, toward the back of the diff.

With the parts in order, Harrigan put the unit together, minus the pinion shaft for now. With the ring-gear side facing up (i.e. the spacer paddle for this side is facing up, the one for the opposite side is at the bottom), he drew a big, fat purple marker line across the unit as a guide. As you'll see, it'll be now easy to tell which way each paddle is facing.

After disassembling the unit, Harrigan gave each coupler a good coat of wheel-bearing grease so they'll stick to the drivers until the pinion shaft is inserted. As we've explained elsewhere, the springs visible at the top of the photo are critical to the Powertrax unit's operation. Stick with us as we demonstrate.

Preparation is done, so installation begins by inserting the couplers into the differential case. Harrigan started with the ring-gear side, which is then held in place with the previously removed C-clip. Note the guideline (arrow), facing toward the installer, as it should be.

The opposite slotted coupler was then installed. Harrigan simply installed the coupler, and then turned the axle until his marks lined up with each other, ensuring that the active spacer paddles are facing 180 degrees apart, as specified. Hold on with that C-clip, though, that doesn't come until later for this side.

With the saddle springs in place, assembly continues by inserting the ring gear-side driver into the housing. Remember, the driver contains the active spacer, and the paddle on the spacer must be aligned with the proper slot on the coupler, facing toward the rear of the differential.

Harrigan made this all easier by simply lining up the mark he'd made during preassembly, ensuring that the spacer paddle is in its slot and facing the proper direction.

The opposite-side driver assembly goes into place in similar fashion, but be patient; at this point, space is getting tight within the differential housing, and a little finesse goes a long way. Note that the active spacer is in place, with its paddle facing toward the front of the diff, opposite of the ring gear-side, as it should be (arrow).

Again, our intrepid Malibu owner made this easier by simply lining up the mark he'd made at the beginning. At this point, the driver teeth are engaged all the way around on both sides, so the Powertrax's inner workings are aligned as they should be, and we're ready to button this thing up.

Keeping the two drivers wedged together, the driver's wheel is rotated until one of the two damping spring recesses in the Powertrax assembly is located. Note the notch for the inner spring inside the spring slot (arrow).

Each damping spring assembly consists of a thin inner spring within a larger-diameter outer spring. These spring assemblies are meant to minimize driveline backlash, and in our experience, that's exactly what they do.

The inner spring is compressed, and the assembly is placed into the spring slot. Make sure the inner spring is seated in its notches, then, still keeping the drivers wedged together, rotate the assembly to the other spring slot and repeated. This photo shows a properly installed damper spring, as well as the use of the provided check block (arrow). If the narrow side of the block fits between the drivers, as shown, you're in clover. If not, seek technical advice and try again.

In the home stretch, it's finally time to install the passenger-side axle C-clip through the slot in the appropriately named slotted driver. Again, things have to be properly assembled since the C-clip slots in both the driver and the coupler must be aligned. Even so, this is a job for the patient, and it's essential that the C-clip be fully seated in its axle groove.

As with many differential units, the last touch is to install the pinion shaft. With the Powertrax, the pinion shaft must be wedged past the eight saddle springs. Using the pinion bolt as a T-handle helps.

With the pinion in place, we can button our Mali's 12-bolt rear back up. Harrigan chose to replace the stock piece with this Summit aluminum girdle-style lid. The slick ARP cover bolts get 25 lb-ft; the bearing cap preload bolts (arrows) get 10 lb-in before they're secured with locknuts. In half-a-day's work, we've got a stronger rearend with greatly improved traction--cutting a full second off our 0-60 time and 3/4 seconds off of our e.t. Nice.


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