C5 or C6 Corvette Drivetrain - Power To The Pavement
Corvette drivetrain upgrading guide
From the September, 2012 issue of Vette
By Barry Kluczyk
Photography by Barry Kluczyk
Tremec six-speed manual transmissions have served the Corvette since the introduction of the C5 generation in 1997. The T56 appeared in all models until the C6 Z06 introduced the stronger Tremec TR6060 in 2006. Two years later, the 430-horse LS3 brought the TR6060 to the Corvette lineup across the board. The '09-up ZR1's LS9 is also matched with the TR6060, which happens to be rated for 700 lb-ft of torque.
The transmission, of course, transfers torque to the rear axle, and here again, the C5 and C6 have featured a number of different rearend assemblies of varying capacities. Not surprisingly, the C6 Z06 and ZR1 models offer the largest and strongest. Beyond what the factory offered, there are aftermarket upgrades for the trans, the rear axle, and everything in between. These are capable of handling performance upgrades ranging from basic bolt-ons and road-course setups to high-boost power adders designed to send a Corvette down the dragstrip in single-digit e.t.'s.
But it isn't quite as simple as ordering a "Viper" upgrade for your T56 or swapping in a Z06 rearend to ensure your modified Vette is best equipped to handle big power. Take the tried-and-true T56 six-speed, for example: While it may not be the most refined manual transmission in the universe, it has nonetheless performed admirably in the realms of performance and efficiency. You just can't beat the satisfaction of clicking into Sixth gear on the freeway and approaching 30 mpg with more than 400 hp on tap.
It's when the engine's output is increased significantly that the T56's limits are revealed. In the C5 and early C6s, this transmission's maximum torque rating was 450 lb-ft. That's fine for most mildly modified street cars, but in this age of 700-, 800-, and even 1,000-horse street engines, the T56 just doesn't have the strength to cope.
1 Broken parts are hard on...
1 Broken parts are hard on the ego...and the wallet. Whether it's a broken transmission, snapped axle shafts, or, as seen here, a shattered differential housing, an insufficiently upgraded drivetrain won't stand up to big horsepower forever.
2 Let's start with the manual...
2 Let's start with the manual transmission. The TR6060 used in LS3-, LS7- and LS9-powered C6s has a 700-lb-ft torque capacity--nearly 56 percent more than the 450 lb-ft capacity of the T56 used in C5s and early C6s. The TR6060 also features triple-cone synchronizers on gears 1-4, a stronger input shaft, stronger shift forks, and other enhancements. Photo courtesy GM
3 A close-up profile of TR6060...
3 A close-up profile of TR6060 (left) and T56 Second gears shows the dramatic difference between them. The TR6060 gear is 1.200 inches thick, compared to the T56 gear's 1.075-inch thickness.
"Once you get to about 700 hp, the T56 is done," says Rodney Massengale, at RPM Transmissions, in Anderson, Indiana. "It's a very good transmission, but it just wasn't designed for the kind of power that LS engines have been pumping out for the last few years."
And what about that vaunted Viper version of the T56? The biggest difference is the output shaft (also known as the main shaft). The Viper unit uses a beefier 30-spline shaft (1.290 inches in diameter), versus the Corvette's 27-spline shaft (1.175 inches in diameter). That's it, really. Some enthusiasts will tout the Dodge's steel 3-4 shift fork, too, but having torn down countless transmissions over the years, Massengale says his technicians find steel forks only occasionally in the Viper versions.
"You can upgrade the T56 with the Viper main shaft and some other internal upgrades, but the gears and synchros will be the same," he notes. "If you really want to step up to the next level, you've got to look at the TR6060."
The TR6060 has its roots in the venerable T56, but it was designed for much more powerful engines such as the LS7 and LS9. It's also more refined, with smoother, more direct shifts.
The TR6060's greater strength comes from larger and stronger components, as compared with the T56. Take First gear, for example. It measures 4.9 inches in diameter and is 0.98-inch thick in the older trans. In the TR6060, First is still 4.9 inches in diameter, but it's 1.19 inches thick--a significant 22 percent increase. It's a similar comparison for all the gears, and the TR6060 also gets a 31-spline output shaft measuring 1.36 inches in diameter.
4 The 3-4 synchros (left)...
4 The 3-4 synchros (left) are larger and stronger for the TR6060, too. This one has a 4.760-inch diameter, compared with the T56 part's 4.115-inch diameter. It also has fine-tooth gear angles, with more teeth (64 vs. the T56's 36, in the case of these examples).
5 The main shaft in the TR6060...
5 The main shaft in the TR6060 (left) is also much beefier, with a 1.360-inch diameter and 31-spline output section vs. the 1.175-inch/27-spline shaft of the T56 unit. The TR6060's thicker shaft contributes greatly to the transmission's higher torque capacity.
6 The 1-2 synchronizer-assembly...
6 The 1-2 synchronizer-assembly retaining ring in the T56 (right) is known to break on occasion. The TR6060 retainer has been upgraded to prevent this potentially catastrophic failure.
7 Both the TR6060 and the...
7 Both the TR6060 and the T56 come with a plastic shifter insert (right), which is prone to wear and cracking. Replacing it with a bronze insert is a must, regardless of the transmission you're using.
8 Bronze fork pads should...
8 Bronze fork pads should be used in place of the factory plastic pads. The pads press onto the shift forks, which move the sliders back and forth to engage the gears. When the plastic pads break or wear, the sliders can't fully engage, causing the transmission to pop out of gear.
9 When it comes to automatic-shifted...
9 When it comes to automatic-shifted powertrains, swapping out the stock four- or six-speed trans for a prepped 4L60E like this one can be an easy way to improve durability and performance. With a factory shifter in the console, the conversion looks OEM, too--even in Z06s and ZR1s.
Your title here...
To put it bluntly, you C6 guys with the six-speed 6L80E slushbox have few options at the moment. There are plenty of aftermarket upgrade systems for four-speed-equipped '05 models and C5s, but the computer "tuning" of the six-speed autos hasn't been fully cracked yet. Accordingly, if the planned rear-wheel output of your Corvette is north of 700 hp, retrofitting a beefed-up four-speed might not be a bad option.
In fact, when it comes to high torque capability, a properly built automatic transmission is sometimes preferable to a manual. Just look at the quickest Corvettes on the dragstrip these days--even the Z06s and ZR1s--which don't run stick shifts. Specially built 4L60E, 4L80E, and even Turbo-400 transmissions are the ways to go.
Switching to a 4L80E or Turbo 400, however, will require surgery. Each is a few inches longer and taller than a 4L60E, so tunnel modifications are needed, along with a shorter torque tube and driveshaft. It's a serious commitment to step up to one of these transmissions, but they're strong and dependable.
"The 4L60E is great for cars running from the 11s into the 9s, as I can personally attest," says Massengale. "If you're aiming for bottom 9s or the 8s, you'll probably want to go with the 4L80E or Turbo 400."
And when it comes to deciding between the two, the three-speed Turbo 400 is ultimately more adaptable for performance use, with a greater range of gear ratios available. It also offers a faster trans brake, and, unlike the 4L80E, there's no lock-up converter. In short, it's a true racing transmission--complete with all the positive and negative traits that distinction entails.
10 Even if the stock transmission...
10 Even if the stock transmission is retained, its main shaft should be swapped out for a stronger one at around 550 rwhp. It's also a good idea to upgrade the differential's output shafts at this power level.
11 When the capabilities...
11 When the capabilities of the 4L60E have been exceeded, a 4L80-series or Turbo-400 (shown) trans may fit the bill. These units weigh roughly 75 pounds more but offer a significant upgrade in strength. The three-speed Turbo-400 is typically preferred for cars that primarily see strip duty, while the four-speed 4L80 is better suited to street use.
12 RPM Transmissions modifies...
12 RPM Transmissions modifies the Turbo-400 (bottom) to fit the C5/C6 chassis, but the car itself also requires alterations. The tunnel must be clearanced, while the torque tube and driveshaft must be shortened. In this photo, you can see the approximately 3-inch-greater length of the Turbo-400, as compared with a 4L60E. It's also a bit wider and taller.
As for the rear-axle system--that is, the differential, axle shafts, and so on--it's once again the C6 Z06 and ZR1 components that deliver the greatest strength. C5 and C6 Corvettes have used a variety of differential housings, with the C5's being the smallest and weakest. While they're all mostly upgradeable, a C6 Z06 or ZR1 housing will bolt right into a C5 chassis using a C6 chassis cradle. The Z06/ZR1 diffs are easily upgradeable, too, with even-heavier-duty components to ensure bulletproof performance on the street or track. The Quaife torque-biasing differential is one notable example.
"The Quaife is the best option for high-powered cars that are going to see some time on the dragstrip or road course," says Massengale. "We can upgrade stock differentials for cars mostly used on the street, using compressed-carbon clutch packs in place of the stock bronze clutch packs, among other modifications. There are also a few aftermarket differentials that provide greater capacity than the stock diff, but for serious power and performance, the Quaife is definitely the way to go."
Unlike other differentials, the Quaife does not incorporate clutch packs. It's strictly gears inside, for maximum strength. Sets of floating helical gear pinions mesh to provide "normal" performance, but in the presence of wheelspin, torque bias is generated by the axial and radial thrusts of the pinions in their pockets. The resulting friction forces enable the differential to transmit a greater proportion of the torque to the appropriate wheel. According to Quaife, it's a progressive process and doesn't entirely lock the diff. At around $995 for the unit alone, it's not a cheap solution, but it's a bulletproof one.
While upgrading a C5/early C6 to the TR6060 trans and a C6 Z06/ZR1 axle will deliver the torque capacity to support a high-horsepower engine combination, Massengale advises that the rest of the driveline needs to be addressed, too.
"The biggest killer of transmissions and rearends isn't necessarily too much horsepower or torque channeled through weak parts, it's abuse and wheelhop," he says. "We've seen cars with only about 400 rear-wheel hp break the differential housing because of wheelhop, and we have customers who send twice that power through a basically stock manual transmission because they know how to launch correctly and shift precisely. The stronger parts are fundamental, but they're no replacement for driving skill."
13 Eliminating the transmission/differential...
13 Eliminating the transmission/differential housing's natural tendency to rotate upward under load helps reduce the chance for wheelhop. One way to do that is to swap the stock rubber transmission mounts (left) for solid ones. The change doesn't make for a comfortable ride on the street, but on the strip, it's a significant contributor to planting the IRS at launch.
14 C5 and C6 Corvettes have...
14 C5 and C6 Corvettes have come with a number of different differential housings over the years. Generally speaking, they've grown larger and stronger with the car itself. This photo shows a range of housings, starting with a C5 "3 series" unit at the bottom right and a C6 "base" housing to its left. On the top row are C6 Z06 (left) and ZR1 housings.
15 The difference in size...
15 The difference in size between a C5 (right) and a ZR1 housing is significant. Note, too, the substantial ribbing on the ZR1 piece, which bolsters strength, along with the integral cooler. It's also cast with a stronger aluminum alloy. The C6 Z06 and ZR1 housings are the two strongest units available, with the ZR1 being the strongest of all.
Massengale walked us through the setup his shop put together for Ohio customer Mark Carlyle, whose Atomic Orange, single-turbo '07 Z06 has run as quick as 7.75 at 183 mph using an automatic transmission and the production-based independent rear.
"Starting at the engine, Mark's car runs a new flexplate and bellhousing, along with a new driveshaft and driveshaft couplers," says Massengale. "The transmission is a Turbo-400, and the differential is a Quaife set in a ZR1 housing. And, of course, the output shafts are stronger, and even the CV shafts and wheel studs are stronger. It's a complete system from end to end, backed up with the right suspension."
Along with the trans and rearend, Carlyle's car runs a racing-spec flexplate, bellhousing, torque tube/driveshaft assembly, and more. That's more than you'll need when bolting a blower onto your C5, but it does illustrate the importance of assembling the right combination.
"It's easy to spend too much on parts you don't need, or to pick the wrong part and wonder what went wrong later. [For this reason] upgrading your driveline shouldn't be done by blindly picking parts out of a catalog or off a website," says Massengale. "Because the production parts are basically interchangeable, it's easy to put together a transmission/axle package that's tailored to the power level of a vehicle. For example, we can use a T56 with a C6 Z06 differential--or match a TR6060 with the ZR1 diff, mount it to a C6 cradle, and slide it up into a C5. You really just need to consult with an expert to pick the right parts for the expected performance level of your car. You'll save money and frustration in the long run."
Be smart and honest about your performance upgrades. If you plan to drive your car primarily on the street and keep its output level below the 700hp threshold, there's no reason to spend the extra money on a TR6060. RPM Transmissions and a number of other drivetrain specialists can deliver a strengthened T56 with a 30-spline output shaft, solid synchronizer keys, bronze fork pads, a steel 3-4 shift fork, and other upgrades for roughly half the cost of a full TR6060 swap. The same goes for the rear axle.
A little forethought will help put your Vette's power to the pavement efficiently--rather than putting expensive parts on the pavement in tiny, expensive pieces.
16 A C6 differential housing...
16 A C6 differential housing will fit in a C5, but it's necessary to swap out the entire rear cradle, which also includes the control arms, CV shafts, and more. Fortunately, it bolts right up to the C5 chassis.
17 Quaife's torque-biasing...
17 Quaife's torque-biasing differential contains no clutches, which can slip and burn out. In their place is a series of hardened pinions that provide positive, slip-free torque transfer. This cutaway photo illustrates the composition of the unit. This is by no means a budget upgrade, but it's the best option for cars putting a lot of torque to the pavement. Photo courtesy Quaife
18 When using the Quaife...
18 When using the Quaife with a C6 Z06 or ZR1 housing, there's only one ratio choice: 3.42. While that doesn't sound optimal for the dragstrip, RPM Transmissions' Rodney Massengale says it works very well for high-revving LS engines that cross the finish line in less than 9 seconds, since it places them in the sweet spot of the rpm band. It's also a great highway gear for street cars.
19 RPM Transmissions worked...
19 RPM Transmissions worked with the Driveshaft Shop to develop output shafts that mirror the shape of the stock shafts, but are made from an aerospace alloy that's stronger than 300M steel. (The manufacturing process lends the shafts a reddish color.) Just as important as the material used is the method in which the splines are created: They're rolled rather than cut or machined. This compresses the material of splines, which strengthens them.
20 One of RPM Transmissions'...
20 One of RPM Transmissions' unique replacement parts is the torque-converter drive plate, shown here below the factory stamped-steel part. At 1/4-inch thick, the RPM plate is 1/8-inch thicker than stock. This provides an exponential increase in strength, and the ability to stand up to 1,000-plus-hp power-adder engines.
21 Next in line for an upgrade...
21 Next in line for an upgrade is the driveshaft. Shown here is one of the Driveshaft Shop's 3-inch-diameter/0.125-inch-wall shafts above the remnants of a stock driveshaft. The Driveshaft Shop's piece also features stronger, billet-aluminum ends.
22 Matched with the stronger...
22 Matched with the stronger driveshaft are stronger couplers. These urethane-based parts, offered through the Driveshaft Shop and used in many of RPM Transmissions' systems, have a higher durometer than the stock rubber couplers, helping them withstand higher loads and critical speeds.
23 Get the combination right,...
23 Get the combination right, and consistent performance is virtually guaranteed. This is Al Brodbeck's C5 Z06, which uses a Vortech blower on a built LS7 to rip a best e.t. of 9.04 at 159.96 mph. The stock drivetrain has been replaced with a RPM Transmissions–built 4L60E automatic, a C6 Z06 differential housing filled with a Quaife diff, and a number of other upgraded components.
24 This photo amply illustrates...
24 This photo amply illustrates the importance of upgrading the couplers. This is a stock unit that was destroyed in a high-power race Corvette. Under high load, the couplers get squeezed out of shape and grow, causing them to rub against the inside of the torque tube and shred.