Tremec’s six-speed gearboxes have been the standard-bearers for manual transmissions in high-performance domestic applications for decades, and for good reason. In factory-stock applications, these transmissions have proven to have both the strength and refinement to provide the three-pedal faithful with many years of trouble-free service, despite the abuse they’re typically subjected to. And that’s one of the reasons that manual transmissions are often overlooked in the pursuit of better performance.
“In a stock state, the T-56 was basically flawless,” says George Kreppein of Rockland Standard Gear in Sloatsburg, New York. “They sold a lot of them, and they really did hold up well.” It’s a good thing, too, because that transmission can be found in everything from the fourth-gen F-bodies to the first three generations of the Dodge Viper — along with plenty of other high-performance models across the automotive landscape.
But the march of time hasn’t been particularly kind to the T-56, and we’re not just talking about the 26 years of botched power shifts. While the aftermarket has been busy developing a vast array of go-fast hardware for the LS and other popular engine platforms, these aging transmissions have been tasked with far more torque, revs, and heat to deal with than they were originally designed for, and that’s led to the untimely death of many a T-56.
Rebuilds are a common occurrence in the performance game, of course. But in the case of this particular transmission, the end-users aftermarket options offer little in terms of strengthening to ensure that they won’t end up in the same spot with another failure due to inherent design limitations. Fortunately, Rockland Standard Gear has developed a solution in the Tranzilla Magnum. We sat down with Kreppein to get the skinny on issues faced with the factory T-56, what Rockland Standard Gear does to address those problems with the Tranzilla, and what this gearbox has to offer for builders who are looking to step up to a better transmission.
Identifying The Weak Links In The Standard T-56
“As engines became more capable of reaching higher RPM, the style of keys and spring assemblies used in the factory units just couldn’t keep up,” Kreppein explains. “So while those engines progressed, the T-56 didn’t. They were more or less the same from 1993 to 2007. And because of the way the design was, the aftermarket-style solid keys would affect shift quality. People just didn’t realize that the weight of the key would hamper high-speed shifts.”
In a nutshell, a transmission key is a piece of metal used in the hub to connect a rotating machine element to the shaft. The original keys in cars like the Camaro, Viper, and Mustang were produced in hardened stamped steel, while aftermarket parts were offered in a powdered metal – a far softer material. “Ninety-nine percent of key failures on the T-56 was due to power shifting without a full release of the clutch,” notes Kreppein. “That’s basically why these keys broke. When the release is good, what happens is the keys and the synchro ring fall into a neutral position, allowing the slider to go across and make the shift. This all happens in a split second. But when you try to force the transmission to shift under power, the keys are locked in a groove in the blocking ring, and they don’t line up with the sliders.”
With only minor iterative changes throughout the years that were based mainly on packaging concerns and other application-specific requirements, this design issue followed the T-56 throughout its life span and continues to do so to this day in aftermarket use. But Tremec also took note of this shortcoming when they designed the T-56’s successor, the TR-6060.
“It pretty much fixed that multiple-key synchronization issue,” Kreppein says. “One through four were all the same sized synchro ring, and they were triple coned for first and second gear, while three through six were double coned. They also changed the key system – it no longer has springs and keys like the T-56, it uses key cartridges which are actually integrated into the synchro hub. That design alleviated the issue that the T-56 had with synchro keys breaking.”
The engineers at RSG saw that they would be facing an insurmountable task if they tried to address the T-56’s design issues by merely retrofitting the gearbox with slightly different components, as the rest of the aftermarket had been for many years to little effect. So they decided to take a different – and far more comprehensive – approach with the Tranzilla.
“The problem is that the T-56 has been more or less made obsolete by Tremec,” says Kreppein. “And that means that the factory gear-train is very difficult to get now. So rather than turning to the aftermarket, we actually build what are basically TR-6060s into T-56 configurations. That’s how we addressed the problem.”
Now you might be wondering why a builder wouldn’t simply opt for a TR-6060 unit to begin with. Kreppein points out that with certain applications, it’s just not that easy.
“It mainly comes down to the packaging. The cars that were originally equipped with T-56s were designed around the dimensions of that setup, and the TR-6060 wasn’t really designed with the intention of being retrofitted into those applications. So what we did was develop all the components needed to take a TR-6060’s internals and fit them into a T-56 box. It’s not really a retrofit – it’s a direct replacement.”
The cars that were originally equipped with T-56s were designed around the dimensions of that setup, and the TR-6060 wasn’t really designed with the intention of being retrofitted into those applications. So what we did was develop all the components needed to take a TR-6060’s internals and fit them into a T-56 box. It’s not really a retrofit – it’s a direct replacement.”
Between ratio availability and different configurations, RSG offers 192 different variations of this T-56/TR-6060 hybrid.
“The Magnum Tranzilla is a hand-built unit with match-fit components to make sure the clearances are minimal, and we use different gear-train, synchronizers, locking rings and overdrive combinations versus what you would get in a typical Magnum,” says Kreppein.
The original Tranzilla builds are made of 9310 alloy steel, 300M main shafts, utilize a steel 3-4 shift fork and solid billet steel synchronizer keys, and feature a gear-train with a 22-degree helix angle for increased strength, less thrust load, and lower operating temperatures. All in, it equates to a seriously stout, direct-fit T-56 alternative that can handle up to 1,200 horsepower and a1,000 pound-feet of torque. RSG also offers a similar build with its 9310 Magnum Tranzilla HD, rated at 1,200 horsepower and 1,000 lb-ft of torque.
But Kreppein is also quick to point out that the performance isn’t solely a product of the transmission itself.
“A lot of it has to do with having a well-configured clutch. The spin-down time in racecars, for instance, has to be fast because they’re shifting up and down constantly. So the smaller the discs, the shorter the spin-down time, and the faster the transmission can shift without causing extra wear.”
Going Plug And Play
Because of RSG’s design approach with the Tranzilla Magnum, there are virtually no limitations in terms of applicable models.
“Any T-56 can be built into a plug-and-play replacement,” Kreppein says. “We can build them as a straight replacement, and we can also build them with updated input and output shafts to hit those higher torque ratings.”
He notes that the Corvette line – available for C5 and 2005-2007 C6 models – is one of the most high-demand markets, but later C6 owners can see benefits from Tranzilla upgrades, as well.
“In the 2008 and 2009 models, they had some synchro issues because the factory only uses sintered metal rings, and what we’ve learned about sintered metal rings is that they’re very nice in a regular street car – they make the shifts smoother and reduce notchiness. But while they have a bit more bite, the carbon ring actually grabs the cone. So in a racecar we’ll always use carbon, but for mixed-use applications, we can use a combination of carbon and sintered metal rings to give you the best of both.”
Along with the Corvette, RSG also supports other American muscle cars, including 1993-2002 GM F-bodies, GTOs, CTS-Vs, Chevy SSRs, all Gen I through Gen III Dodge Vipers, Challengers, Ram SRT10 pickup, and Ford Mustangs equipped with the MT82, as well as the Terminator Cobras and GT500 models equipped with the TR-3650.
The Virtues Of Adaptability
While the added strength of the Tranzilla gearbox is perhaps its most obvious benefit, RSG’s ability to tailor these transmissions to the needs of builders is a massive boon, not only for durability, but performance potential, as well.
“We build more close-ratio boxes than anything else,” says Kreppein. “Most cars have a 1,500 RPM drop between gears – when you upshift from gear to gear, the revs go down by about 1,500 RPM. When you move to a close-ratio setup, that drop down is reduced tremendously, and you stay in the engine’s power band rather than waiting for the engine to recoup the RPM.”
For both road racing and street cars used in a similar context, having a close-ratio box can be a massive improvement in overall response versus a factory gear set, where higher ratios tend to favor fuel economy and other OE requirements rather than outright performance.
We build more close-ratio boxes than anything else. Most cars have a 1,500 RPM drop between gears – when you upshift from gear to gear, the revs go down by about 1,500 RPM. When you move to a close ratio setup, that drop down is reduced tremendously, and you stay in the engine’s power band rather than waiting for the engine to recoup the RPMs.
Kreppein states, “On a street application, where most guys are running 3.73 or 3.90 rear end gears, with a 2.29 first gear, the only time you might not love it is if you’re stuck in traffic – otherwise it’s pretty ideal.”
But ratios and component materials aren’t the only options when it comes to the Tranzilla.
“We also offer various shifter locations,” Kreppein notes. “From the face of the bellhousing to the shifter, we offer 25-, 26.25-, 29-, 33-, and 36-inch spacing locations. That can be a big benefit to cars like the GT500, the Dodge Challenger, and the fifth-generation Camaro, which use remote-mount shifters. In a remote-mount setup, you’re dealing with bushings, linkage and all of these changes in direction to get it to work. With the Tranzilla Magnum, you can get rid of any slop in applications like these by moving to the shifter to a location that gets rid of that extra hardware so you can use a direct-mount setup.”
Speaking of bellhousings: RSG offers some options there, as well. “For 2010 and up Camaros, we also offer an SFI bellhousing,” Kreppein says. “A lot of rule sets, both at tracks and within sanctioning bodies like the NHRA, want you to have an SFI-certified bellhousing or a blanket. But with the heat these cars generate, you can just bake the clutch with those blankets, so this bellhousing helps to keep everything cool while staying in compliance with those rule sets.”
RSG even has something for off-road enthusiasts.
“The 4×4 guys are very limited by how many standard transmissions are out there, and there are even fewer that shift like a performance transmission rather than a truck transmission,” notes Kreppein. “So we build a four-wheel drive version of the Tranzilla Magnum, too. There’s a multitude of output shafts available, and it comes with an adapter which can be easily set up for whatever your drop angle is for the front driveshaft – you’re not fixed to one drop angle, so you can mount your transfer case anywhere you want. It also means you can get those benefits of close-ratio gearing, improved shift quality, and capability of servicing it in the future – you can buy parts for it anywhere, because those components are still in production today.”
Whether it’s for the street, track, or dirt, RSG’s goal with the Tranzilla Magnum is to provide builders with peace of mind that the gearbox they’re using is purpose-built to take the abuse they’re going to dish out.
“We test our parts at 200 miles per hour,” Kreppein adds. “Whether it’s for an endurance race car or a street car that goes back and forth to shows, we build our transmissions the same way. In our world, consistency is absolutely key – what you pay for is what you get.”