T56 Transmission Torque Doubling - No Guts, No Glory

From the August, 2012 issue of GM High-Tech Performance

By Barry Kluczyk

Photography by The Author

The innards of the Tremec TR6060 effectively double the torque capacity of a T56 transmission--and we show you how to make 'em work for your Fourth-Gen F-body and other LS cars

For fourth-gen F-car jockeys – as well as the third-gen enthusiasts who've made the swap – the Tremec T56 six-speed manual transmission has been a source of both satisfaction and frustration. On the street and on the freeway, it's a suitably strong transmission that delivers generally excellent performance – even if it's not the most refined-feeling transmission. And we don't know anyone who complains about clicking into sixth gear on the freeway and pulling down mileage in the high 20s, while the engine loafs along barely above idle. When you start leaning on the T56 harder, however, the edge of its performance envelope begins to show. In its F-car form, it was rated for 450 lb-ft of torque, while the vaunted Viper version was rated at 550 lb-ft. That was just fine 10-15 years ago, but as time marched on, so did the rear-wheel output of LS-based street/strip machines. You can exceed the torque rating by merely slipping in a hotter camshaft in an LS7 crate engine. Add a power adder to just about any well-tuned LS engine these days and you'll be asking too much of your T56 at the drag strip.

"Once you get to about 700 horsepower, the T56 is done," says Rodney Massengale, at RPM Transmissions, in Anderson, Indiana. "It's a very good transmission, but just wasn't designed for the kind of power that LS engines have been pumping out for the last few years." And what about the Viper version of the T56? The biggest difference is the output shaft (also known as the main shaft). The Viper version uses an admittedly beefier 30-spline shaft (1.290 inches in diameter) versus the F-body's 27-spline shaft (1.175 inches in diameter). That's it, really. Some enthusiasts will tout the Viper transmission's steel 3-4 shift fork, too, but after tearing down countless transmissions over the years, Massengale says his technicians find steel forks only occasionally in the Viper versions – but, interestingly, they're always in the T56s used in 2003-04 Mustang Cobras. "You can upgrade the T56 with the Viper main shaft and some other internal upgrades, but the gears and synchros will be the same," says Massengale. "If you really want to step up to the next level, you've got to look at the TR6060."

The Tremec TR6060 was the answer for GM's most recent stable of factory-built super cars, like the C6 Corvette Z06 and ZR1, the fifth-generation Camaro SS and the second-generation Cadillac CTS-V. The TR6060 has its roots in the venerable T56, but designed for much more powerful engines – with a torque rating of 700 lb-ft. That's serious capacity from a factory-built manual transmission. It's also a much more refined transmission. And just to be clear: You Pontiac G8 guys are running the TR6060, too, but GTO drivers are rowing the T56. The 2004-07 Cadillac CTS-V uses the T56.

On a recent visit to RPM Transmissions' new headquarters in Anderson – about 25 miles north of Indianapolis – we got a side-by-side look at the differences between T56 components and TR6060 parts. The comparison was dramatic. At a glance, it is easy to see the TR6060 gears, synchros, bearings and other internal parts are simply larger and stronger. Even the Magnum transmission case that holds the TR6060 guts is thicker in key areas. It's simply an all-around stronger setup.

Sounds great, right? But there's a problem for the F-body crowd: A salvage/take-out TR6060 from a Camaro SS, G8 or CTS-V won't bolt into a fourth-generation, LS-powered Camaro or Firebird. It just won't go. The length is wrong, the tail shaft doesn't have the torque arm mounting points and the front plate/bell housing is different, too – and the shifter location is just-plain incompatible. Tremec sells the T56 Magnum transmission as a universal-style aftermarket piece with the guts of a TR6060 stuffed in a die-cast aluminum T56 case. But again, it's not a bolt-in for F-bodies, because the bell housing and tail shaft are incompatible – especially the tail shaft, which is too long and has the wrong shifter location for a Camaro/Firebird. RPM Transmissions has a solution: They modify the Magnum transmission to make it a direct bolt-in for a fourth-gen F-body. It will work, too, in third-gen cars.

In a nutshell, RPM Transmissions starts with a brand-new T56 Magnum, disassembles it, whacks off about three inches from the rear of the main shaft, swaps the factory Magnum tail shaft with an F-body tail shaft and builds a custom shifter rail to replace in factory rail. Of course, it's a bit more complicated than that, but the end result is a transmission with a torque capacity nearly 60 percent greater than the T56 – and one the slips into the F-body chassis as a direct bolt-in. You simply add a new, 31-spline yoke and the stock driveshaft snugs right up to it, too. This modified Magnum trans runs about $5,000 out the door, which may seem steep, until you consider you could spend about half as much on a high-performance T56 rebuild, but will still end up with about half the torque capacity of the TR6060 – even if you add the Viper main shaft.

Be smart and honest about your performance upgrades. If you plan to drive your car primarily on the street and keep its horsepower level below the 700 threshold, there's no reason to spend the extra money on TR6060 guts. RPM Transmissions and a number of other transmission specialists can deliver a strengthened T56 with the 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 the TR6060-ized transmission. But it you're going for big power, the insurance of the strongest Tremec available makes the extra investment seem not so great.

In the accompanying photos, we've illustrated the key differences between the T56 and TR6060 gear sets, along with the some of the features that are used to either upgrade a T56 or distinguish the TR6060. We've also followed RPM's conversion of a Magnum aftermarket transmission to an F-body-specific version. And what about those of you with a GTO, first-gen CTS-V or C5/early-C6 Corvette (LS3, LS6, LS9 cars feature the TR6060)? Well, the C5 solution is pretty easy, although a bit more expensive, as it involves mating the Magnum case and a modified output shaft with a Corvette transaxle – and if you're stepping up to the strength of a TR6060, you'll probably want to match it with a C6 Z06 or ZR1 differential. As for the GTO and 2004-07 CTS-V, RPM can build a TR6060 for those applications, as well.

No matter which route you choose, if you're high-powered LS ride doesn't have the right guts in its transmission case, you'll never enjoy all the glory of its performance.