The Eaton Truetrac LSD and a Road-Raced Fifth Gen Camaro
Back in March we detailed Mike Franz’s 2013 1LE Camaro – a ride that’s built to handle the twisties and put down a solid amount of power while doing so.
The car has seen a number of upgrades, from the American Racing Headers long-tubes underhood to the custom-ground COMP Cams bumpstick designed to pump up the 6.2L LS3 engine. An Airaid cold-air kit is also on the job, and with these modifications, the car makes 472 horsepower and 432 pound-feet of torque at the wheels on the dyno at Cunningham Motorsports in California, where Franz works as the right-hand-man to shop owner Ryne Cunningham.
The stock 1LE suspension, already upgraded from the standard Camaro’s underpinnings by GM, has been further enhanced as Franz has a set of high-performance sway bars and drop springs on board to assist the 1LE parts in hustling the car around a road course and through its daily job of shuttling him to and from the shop.
The 1LE package is offered on 1SS and 2SS coupe models, and offers a substantial number of upgrades over the standard SS package. Monotube rear dampers, a strut tower brace, higher-capacity rear-axle half-shafts, new toe links and rear shock mounts – the list goes on and on. Chevrolet installed a 3.91:1-geared limited slip differential at the factory, but Franz was looking for an upgrade and better traction in all situations; this is where Eaton Performance comes into the picture, with one of the company’s Detroit Truetrac differentials.
What Is It?
Put simply, the Detroit Truetrac is a differential unit that maximizes traction in all situations without any input required from the driver. For road racing and track days, this is especially important as it will allow Franz to perform better on the track.
Engineering The Fifth Gen Truetrac Fitment
Fitting the Truetrac into the 5th Gen platform required special considerations during the engineering process. Since the 5th Gen uses an independent rear suspension, Eaton had to change a couple of the dimensions compared to a standard live-axle Truetrac. The pilot on the axle shaft where it enters the differential’s bearing journal is unique, so it had to be re-engineered to work properly.
The 5th Gen Truetrac is designed to accept stock or aftermarket 31-spline half-shafts and requires only traditional 80W90 gear oil, with no friction modifiers added to the mix. In fact, Eaton also stresses that unlike the stock limited-slip differential, the Truetrac needs resistance to work properly, so conventional oil is specified over “too-slippery” synthetic oils.
The Truetrac is very different from traditional limited-slip differentials, which rely on plate clutches or cone-type clutches to manage torque and transfer power between the wheels. One of the chief responsibilities of a differential is to allow the wheels to run at different speeds, such as in a corner, where the inside wheel is turning more slowly than the outside wheel – it has to travel a shorter distance, thus the slower speed.
In a clutch-type differential, there is a spring pack in the center of the unit that press the side gears against the clutches, which are held in place by the differential case. When the wheels are moving at the same speed, the side gears spin with the housing, and the clutches are just along for the ride.
When a vehicle enters a turn, the clutches fight the behavior of one wheel wanting to turn more quickly than another – the wheel must overpower the clutch to achieve the different speed (thus the name differential). The stiffness of the spring pack, combined with the friction material of the clutches, determine how much torque it takes to overpower the assembly and allow the wheels to run at different speeds. A cone-style differential works in much the same way, except the clutch packs are cone-shaped rather than flat.
Inside The Truetrac
Where a Truetrac differs from the above mentioned differential designs is that there’s not a single clutch to be found in the unit – it operates silently, with a set of helical gears that mesh together to split the torque when required.
“All limited-slip differentials rely on natural gear-separation forces one way or the other to bind themselves up. They don’t actually lock, they bind. When the torque starts escaping out of one wheel – one wheel starts to slip and spin faster than the other – now the internal workings of the differential are spinning independent of the case that they’re housed in. When you’re going straight, all of the rotating components are working as one unit. Everything is being driven by the ring gear that’s bolted to the differential. When torque is applied, and the wheels start to slip, the helical gears in the Truetrac bind themselves up in the channels of the differential case to provide traction to both wheels as they can handle it,” says Gwozdz.
How It Works In Pictures
The Truetrac has the ability to dramatically reduce lap times because of its ability to transfer up to 70 percent of the torque load. – Barney Gwozdz, Eaton Performance
Internally, there are six helical pinion gears (three pairs) that remain locked to the side gears when torque is being applied equally to both axles. As traction needs change, the gear separation forces take effect, transferring the power to the wheel with the highest traction – ensuring that the vehicle continues moving forward and improving the overall handling of the vehicle.
The separation forces create friction between the pinion gears and the gear pockets, which increases until the wheel spin is slowed or completely stopped – keeping the tires firmly planted to the road and the power distributed to the wheel that can use it most. Additionally, since there are no clutches or springs to wear out or become soft over time, the Truetrac can boast lifetime torque bias retention.
The Truetrac Applied To Road Racing
“The Truetrac allows you to power through the corner. Instead of coasting through a corner and powering out at the very end, the Truetrac will allow you to power through the corner and minimize traction loss. With a lot of limited-slips when you lay on the hammer and go around a corner, you end up going sideways due to a loss of traction – which is losing speed – and the Truetrac minimizes that,” says Gwozdz.
The Truetrac relies on a steel gear case and alloy internals, which are designed to handle high shock loads found during standing-start launches in addition to the stresses put upon the differential in road course applications. During our conversation, Gwozdz recounted that he had done a like-for-like swap in a different car a few years ago at the Mid-Ohio road course and noticed an immediate improvement in the car’s overall behavior. The Truetrac behaves the same in all applications – you just put the power to it and go.
The Install And Performance
Getting to the the differential on a 5th Gen Camaro is a time-consuming job that requires a number of components to be removed in order to extract the differential housing for the change to the Truetrac. The wheels, exhaust, driveshaft, and rear control arms all need to find a secure temporary home away from home in order to begin the swap process. While the removal process is underway, the existing fluid should be draining from the differential housing.
Also removed at this time are the axles, which are disconnected from the hub, then pried from the sides of the differential housing and set out of the way. Three bolts are removed from the differential mounts, and you can go ahead and pull the pumpkin out from underneath the car. It’s not light, so make sure you’re ready to pick it from its place and set it on the bench. Have extra hands ready if necessary – your toes will thank you later.
Once the pumpkin was on the bench, the process to swap out the differential isn’t much different from any other platform – the whole struggle in this instance comes when removing all of the ancillary parts to get the pumpkin to the bench. Remove the cover bolts, a bit of prying on the case with a long bar to sneak the differential out (or you could use the specified case spreader) and the differential can be removed. Follow along with the captions for more install tips.
After the car was all wrapped up, Franz took it for a quick spin, and has been putting miles on it ever since. “I love it – the power engagement is nice and smooth. There’s a definite difference there, especially around corners. I can give it more throttle in the same situation than I could before. The install went easily too. We checked the gear pattern after installing it, and we’ve found that these are designed and manufactured to such close tolerances, in many cases we’re able to just swap them for the factory differential.” he says. He did caution that’s only his experience and not always the case, but seeing as how he says he’s done around 30 of these swaps in recent months we’d say he’s pretty well-versed in what it takes.