A rebuilt T56 is only as good...
A rebuilt T56 is only as good as who screws it back together. Rather than cheap out on a backyard rebuild, we went straight to the source and had it done right at Rockland Standard Gear. Here, a freshly re-bop'd T56 awaits its new owner.
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?
Our gearset was treated to...
Our gearset was treated to a Super Finish polishing process. Compared to a stock gearset (left) it greatly reduces stress risers that can riddle the teeth and cause premature wear. In addition, it helps with lubrication and promotes quieter operation. This service sells for anywhere from $250 to $450, depending on the version of T56 that you have (Corvette or otherwise).
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.
Located on top of the main...
Located on top of the main case is the shift gate plate, which actually sits forward of a Camaro's shifter pad. Having this Super Finished by Rockland promotes slicker shifting and smoother gear change operation.
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."
 No transmission job is complete...  No transmission job is complete without a quality high-performance clutch. Considering the nature of our LS1-powered project car that has already run a best of 10.16 at 138 mph, we didn't want to skimp out. To meet our street/strip expectation, we relied on Zoom for one of its excellent clutch packages that includes a beefy Kevlar-lined disc and stout pressure plate covered in its trademark purple paint. The Kevlar clutch kit was coupled with a billet steel flywheel (same weight as stock) and a newer-style LS1 throwout bearing assembly for smooth actuation and incredible bite. |  Using two circular magnets,...  Using two circular magnets, a T56 is well protected against aquatic-borne materials that could wreak havoc on gears and synchronizers. T56s are one of the few transmissions in the world that boast such designs from the factory. We wiped everything down before assembly and chased every remaining particle down with a handheld magnetic tool. |  Here is an exploded view of...  Here is an exploded view of our T56 before reassembly. As you can see, T56s rely on a bolt-on frontplate for easier serviceability and a rear tailhousing that houses the two overdrive gears (Fifth and Sixth) and of course, Reverse gear. Note that there are two shifter locations possible at the top of the T56. Camaros use the rear opening while Corvettes use the forward one and use a very short tailhousing. |