When the gods above blessed us with the six-speed T56 gearbox, we were beyond words. Here was this slick-shifting internal-rail gearbox built like a brick poophouse that could handle immense amounts of torque without breaking a sweat and, best of all, it bolted right up to any Chevy engine. The LT1 owners soon discovered that 500 or more rear-wheel horsepower could course through the T56's veins with little-to-no consequence.
Not long after, traditional small-block enthusiasts began retrofitting these boxes into their older rides with incredible results. These gearboxes ultimately proved themselves durable on the street and bulletproof on the track.
Having seen the inner workings of a T56 firsthand, we can certainly understand why the T56 is such an incredible transmission, right out of the box. Ease of service, robust construction, and lightweight design all come together in what must be the best six-speed on the planet. If there was anything we could wish for, it would be Fifth being a direct 1:1 ratio for a tighter ratio set between First through Fourth gears. But we're being a picker of nits at that point because, really, what is there not to love?
As time passed, T56s started showing up at transmission shops at rebuild time. Many technicians treated it like any other transmission, often forgetting key processes while reassembling it, never realizing how significant the little details could make the T56 better than it was new. For instance, by blueprinting a T56 for minimal endplay, overall torque capacity can sometimes improve by as much as 40 percent. So when it came time for us to rebuild the T56 in one of our LS1 Camaro projects, we decided to go to Rockland Standard Gear.
Located in Sloatsburg, New York, Rockland Standard Gear is a company that specializes in all sorts of on- and off-road performance drivelines. From rock-smashing transfer cases in rugged four-wheel-drive trucks to American Le Mans race series transmissions, Rockland has been versed in racers' needs for many years. We knew that Rockland's experience would be overkill for our measly street-driven and occasionally strip-beaten Camaro, so we went with its Race Ready rebuild that ups the torque capacity of the factory T56 to a staggering 650 lb-ft of torque. As a point of reference, the T56s that were installed in the '93-02 Camaros and the '97-present Corvettes were/are factory rated anywhere from 400 to 450 lb-ft capacity.
As the vice president of the remanufacturing division at Rockland Standard Gear, George Kreppein Jr. showed us all the tricks that he had up both of his sleeves and didn't hesitate to tell us what works and what doesn't. Case in point: He wholeheartedly recommends carbon-fiber OE synchronizers and billet synchro keys with a steel shift fork on the commonly weak 3-4 gearset, but finds no value in bronze fork pads. He explained that the nylon OEM-style fork pads work very well and that the metallic units just beat up and wear the slider grooves unnecessarily.
As for why T56s fail, Kreppein mentioned that the reasons are typically ... er ... typical. That is, it's not usually the transmission's fault but everything that it's surrounded by. As he related, "The biggest cause for failure on these T56s is lubrication, which is the cause of most of the damage we see. Not enough fluid and the bearings and synchros get burned out real quick. Then it's usually the clutch. Most racers put in a heavy aftermarket clutch with one or two discs and it beats up the synchros real fast."
Kreppein warned us not to use a clutch disc setup that is much heavier than stock. If you think about it, it makes perfect sense. When rotational weight is added to the input shaft, it adds momentum and makes it harder for the synchronizer to slow down or speed up the gears inside to match them together as you reach for the next cog. This will wear the synchros quicker and make your transmission rough shifting in short order. This issue is more common on C5 and C6 Corvettes because, unlike Camaros, they come with an incredibly long (read: heavy) input shaft extension, and the use of a multi-disc clutch just makes an already bad situation worse.
Lastly, Kreppein added, "The most uncommon cause for failure is driver error by either missing a shift or going into the wrong gear. The mechanical failure rate on these T56s is so rare, it's scary. You hardly see broken gears or hard parts. This transmission is one of the best engineered in the industry, and I've seen them all."
A highly recommended option is a Super Finish micro polish for all the internals that help reduce operating temperatures and silken shift action for an extra $250 (prices vary up to $450, depending on the application of your T56.) This process may add seven days to the turnaround time on your gearbox, but we think it's worth it.
Kreppein also emphatically recommends a good synthetic fluid to keep temps down, improve synchronizer action, and prevent foaming. Because Rockland has done so much testing in road race environments, it has come up with its own line of synthetic transmission fluid branded as "Tranzilla." It is designed to work with Rockland's own line of transmissions, but will work perfectly fine with your existing gearbox.
So, we went with his fluid recommendation and heeded his word on clutches by matching our freshly Race Ready T56 with a proven Zoom single-disc Kevlar clutch and matching billet steel flywheel for reliable performance. Trademark features to the Zoom Kevlar setup include incredible clamping force, reasonable pricing and minimal pedal effort-all three attributes are ones that we can certainly live with. Besides, we were digging the purple paint.
If you choose to buy one of Rockland Standard Gear's in-stock boxes, then it will save you tons of time, but of course, will add to the total out-the-door price. For those who chase horsepower like it's covered in blond hair and tight jeans, Rockland Standard Gear also offers its Tranzilla series of transmissions that includes a custom gearset made of a unique proprietary alloy that can handle an incredible 1,200 lb-ft of torque (read sidebar). Although it was offered to us, we thought it would have been more realistic to live with the standard $1,695 Race Ready rebuild.
Once completed, we reinstalled this gearbox into our 10-second '01 Camaro test vehicle. The Zoom clutch held up to the hellacious punishment without a peep and on the street, its silken action made driving a pleasure. In the end, any rough-shifting T56 deserves a thorough rebuild done right. Just make sure that the next time you plan a project that will include a T56 gearbox, have it gone over properly and let an expert go through it, not some fly-by-night operation. You'll save yourself considerable amounts of time and energy in the end.
As you know, the T56 has been the favorite six-speed of choice by the Big Three for all of its performance applications. From Viper GTS Coupes to Z06 Corvettes and even SVT Mustang Cobras, this gearbox has come in many different forms over the years for specific applications. As such, different variants have come out of the T56's Tremec factory in Mexico, allowing the aftermarket to mix and match its own combination of OEM parts to make transmissions handle immense amounts of torque. But Rockland Standard Gear goes a step further and offers its own unique 9310 alloy gearset for the T56 and calls the finished product the "Tranzilla T56."
The Tranzilla T56 is designed to handle 1,200 lb-ft of torque (yikes!) and is available with an incredible variety of ratios as steep as a 2.29 or as short as 2.98 for First. Ratios for all the remaining gears can be suited for your needs as road racers and drag racers alike would want to take advantage of the four available combos. The gears themselves have a less helical profile (of just 22 degrees) to handle more torque. It does increase gear noise ever so slightly, but the increase in power capacity is certainly worth it. Units retail from $5,200 to $8,200, depending on the applications, and come with a one-year unlimited mile warranty. This is the T56 to get if you're serious about power.
In total, the sum of all these parts allows you to pound ludicrous amounts of power to the ground. Just pray that the rest of your driveline can handle it.