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."