The fourth-generation F-car remains a staple of the LS performance world, thanks to its relative affordability and adaptable architecture. But while the platform itself remains a constant, the progress of engine performance continues to march steadily forward, straining some of the F-body’s capabilities.
“Once you get to about 700 horsepower, the T-56 is done,” says performance transmission guru Rodney Massengale of RPM Transmissions (rpmtransmissions.com). “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.”
The Viper version isn’t exactly the answer either. It uses an admittedly beefier 30-spline output shaft (1.290-inch diameter) versus the F-body’s 27-spline shaft (1.175-inch diameter), but that’s about the extent of the differences. 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 only occasionally find steel forks in the Viper versions. It’s not a sure thing—but, interestingly, they’re always in the T-56s used in ’03- 04 Mustang Cobras.
“You can upgrade the T-56 with the Viper mainshaft 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 TR-6060.”
The Tremec TR-6060 was the answer for GM’s most recent stable of factory-built supercars, such as the C6 Corvette and fifth-generation Camaro performance models. It has its roots in the venerable T-56 but is 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 the “guts” of Tremec’s aftermarket-based T-56 Magnum transmission.
The TR-6060’s greater strength comes from larger and stronger components, when compared to the T-56. Take First gear, for example: it measures 4.9 inches in diameter and 0.98 inches thick, but in the TR-6060, First gear is still 4.9 inches in diameter, but is 1.19 inches thick—a significant 22 percent increase that delivers exponentially greater strength. It’s a similar scenario for all the gears, and when it comes to the output shaft, the TR-6060’s 31-spline shaft measures 1.36 inches in diameter.
That’s all well and good, but the TR-6060 from a late-model Camaro SS isn’t a direct swap for the T-56 in a fourth-gen car. The length is wrong, for one thing, and the tailshaft doesn’t have the torque arm mounting points. Also, the front plate/bellhousing is different and the shifter location is simply incompatible.
The aftermarket T-56 Magnum version has the beefier innards of the TR-6060 in an aluminum case that is pretty much a duplicate of the fourth-gen case, but it’s not a bolt-in solution for the fourth-gen cars, either. The bellhousing and tailshaft are incompatible, especially the tailshaft, which is too long and has the wrong shifter location for an F-body.
RPM Transmissions’ solution modifies the Magnum transmission to make it a direct bolt-in for a fourth-gen F-body. It will work, too, in third-gen cars. We visited their shop in Anderson, Indiana, to see how they made the changes to adapt the Magnum transmission and took the time to compare the components of the TR-6060 with the fourth-gen T-56. The differences are dramatic, with the TR-6060 gears, synchros, bearings, and other internal parts simply being larger and stronger. Even the Magnum transmission case that holds the TR-6060 guts is thicker in key areas. It’s simply an all-around stronger setup.
For the record, RPM’s modified Magnum 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 T-56 rebuild, but will still end up with about half the torque capacity of the TR-6060, even if you add the Viper mainshaft.
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 TR-6060 guts. RPM Transmissions and a number of other transmission specialists can deliver a strengthened T-56 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 TR-6060-ized transmission. But if you’re going for big power, the insurance delivered by the strongest Tremec available makes the investment worth every penny.
01. The Tremec T-56 Magnum is built with the “guts” of the TR-6060, which includes triple-cone synchronizers on gears 1-4, a stronger input shaft, stronger shift forks, and additional enhancements over the T-56 that enable a 700 lb-ft torque capacity. (Photo Courtesy GM)
02. This comparison shot shows the TR-6060/Magnum gears side by side with their T-56 counterparts (the TR-6060 gears are on the left of each pair). Look closely and you’ll see the TR-6060 parts are generally beefier.
03. A close-up profile of TR-6060 (left) and T-56 Second gears shows the dramatic difference between them. The TR-6060 gear is 1.200 inches thick, compared to the T-56 gear’s 1.075-inch thickness. That’s a 15 percent difference, which helps illustrate why the TR-6060 has nearly twice the torque capacity.
04. Another comparison shows the input shaft with Third gear. Note the significantly larger tapered roller bearing on the TR-6060 component (top), which will take much more load than the T-56’s smaller input bearing.
05. The 3-4 synchros are larger and stronger for the TR-6060, too (left). The one in the TR-6060 measures 4.760 inches in diameter versus the T-56 part’s 4.115-inch diameter. It also has fine-tooth gear angles, with more teeth than the T-56—64 teeth compared to the T-56’s 36 teeth, in the case of these examples. Triple-cone synchros are used on gears 1-4 on the TR-6060, with double-cone synchros on gears 5-6, which really helps give the transmission a smoother feel.
06. The mainshaft in the TR-6060 (left) is much beefier than the T-56 shaft, with a 1.360-inch diameter and 31-spline output section versus the 1.175-inch/27-spline shaft of the T-56. The TR-6060’s thicker shaft contributes exponentially to the transmission’s greater torque capacity.
07. The cluster gears may look identical, but upon closer inspection the TR-6060 has wider gears (top) and larger front and rear bearings, which withstand a much higher load capacity.
08. Here are the T-56 and TR-6060 Fifth- and Sixth-gear driven gears. The main advantages of the TR-6060 are wider gears, along with separate construction. That allows RPM to change the Fifth and Sixth gear ratios independently. Since both gears are fully splined, they are stronger on the mainshaft.
09. The 1-2 synchronizer assembly retaining ring in the T-56 (right) has proven to be problematic and is known to break on occasion. The TR-6060 retainer has been upgraded to prevent this potentially catastrophic failure.
10. T-56 single cone rings (right) have much less surface area for friction than the new TR-6060 design. This is another feature that makes the TR-6060 superior in the shifting department, once RPM makes their refinements.
11. Both the TR-6060 and the T-56 come with a plastic shifter insert that is prone to wear and cracking. Replacing it with a bronze insert (left) is a must regardless of the transmission you’re using.
12. The cases of the T-56, TR-6060, and Tremec’s Magnum aftermarket transmission are similar at a glance, but the Magnum/TR-6060 case (bottom) is stronger in key areas, both outside and inside. All are made from die-cast aluminum, but the thicker TR-6060 case and larger gearsets inside add approximately 20 pounds to an assembled transmission versus a comparable T-56.
13. This close-up shows the thicker flanges of the TR-6060/Magnum (right) compared to the T-56.
14. Here’s why the TR-6060/Magnum transmission isn’t a bolt-in swap for vehicles originally equipped with the T-56: The tailshaft (left) is about 3 inches longer than the T-56, although the shifter position is farther forward. This just won’t work in your fourth-gen F-body. Besides the length and shifter issue, there’s no mounting point for the fourth-gen torque arm.
15. The TR-6060 front plate (left) is much stronger than the T-56 counterpart. It offers much-improved frontal bracing, as well as larger input and cluster bearings. The TR-6060 is also cast with provisions for a mechanical cooler pump, like the factory-equipped ones found on the Corvette Z06, ZR1, and fifth-gen Camaro.
16. The TR-6060 front plate incorporates a roller bearing for the front of the shifter shaft, as well as in the case. This allows for much smoother shifting operation over the standard Babbitt-material bushings in an early T-56.
17. Bronze fork pads should be used in place of the factory plastic pads. The pads press onto the shift forks, which move the sliders back and forth to engage the gears. When the plastic pads break or wear, it doesn’t let the slider fully engage the gear. This can cause the transmission to pop out of gear after moving the shifter into that gear.
18. RPM Transmissions’ T-56 Magnum packages blend the guts of a TR-6060 with a custom package designed for fourth-gen F-bodies. A $350 option on the basic Level IV package and standard on the Level V and VI packages is micropolishing of the gearsets, which helps reduce friction to enhance performance and durability. Check out rpmtransmissions.com for a complete look at their packages.
19. After all the components are disassembled and micropolished, the transmission is carefully reassembled by technicians who know these parts like the backs of their hands. Here, the 1-2 synchronizer assembly is slipped into place. The sliders and hubs are hand-fit.
20. Here, the die-cast aluminum case is slipped over the gearsets. To fit the fourth-gen F-body, the TR-6060 mainshaft is cut down by approximately 3 inches.
21. The welded area shows a necessary modification to the F-body tailhousing in order to install the single-piece cluster of the TR-6060. It allows RPM to install the newer-style TR-6060 rear cluster bearing.
22. For the TR-6060/Magnum transmission to work in the fourth-gen F-body, the factory shifter rail must be replaced. RPM Transmissions makes their own and inserts it (arrow). By the way, the shifter location in the case is unused in the F-body, as well as the fifth-gen Camaro and other applications. A block-off plate will seal off this section, as the shifter is mounted in the tailshaft.
23. RPM Transmissions uses new fourth-gen F-body tailshafts to complete the conversion of the Magnum T-56. Without it, the transmission won’t bolt up to the F-body chassis.
24. A Viper tailshaft seal is used to match the 31-spline TR-6060 output shaft with the F-body tailshaft.
25. This close-up of the tailshaft shows the all-important mounting provisions for the fourth-gen torque arm, along with the vehicle speed sensor and Reverse solenoid. Again, the TR-6060 doesn’t have these provisions, and the production T-56 Magnum transmission comes with a Ford speed sensor, making RPM’s conversion all the more necessary.
26. With the bronze shifter insert in place, a pin holding the shifter mount to the custom shift rail is tapped in place, effectively finishing off the conversion of the Tremec T-56 Magnum with TR-6060 guts.
27. Here’s the final, assembled transmission. As shown, the cost for this conversion to a fourth-gen bolt-in is about $5,000—not quite twice as much as a full-blown T-56 upgrade, but with twice the torque capacity. Bring on the power-adders!
T-56 Super Magnum Installation Kits Now Available From Chevrolet Performance
Chevrolet Performance has developed installation kits that allow the T-56 Magnum—dubbed Super Magnum in their catalog—to bolt right up to small-block, big-block, and LS engines, and even the all-new Gen V LT1 crate engine. It’s a tremendous advancement for builders looking to hook up a manual transmission for every kind of V-8 offered in a Chevy since 1955. Generally, the kits include a bellhousing and the pilot bearing, as well as a clutch and pressure plate. The new kits include the following applications:
- LS engines with a six-bolt crankshaft flange (PN 19301625). It includes a fourth-gen F-car-type bellhousing and LS7-type flywheel, clutch, and pressure plate.
- LS and LT engines with an eight-bolt crankshaft flange (PN 19329912). This one is for LSA and Chevrolet Performance crate engines, including the LSX376B-15, LSX454, and LSX454R. It’s also the kit required for the new LT1 crate engine.
- Small-block with one-piece rear main seal (PN 19329900). It includes a 1986-later-style flywheel, along with the clutch kit and bellhousing. A big-block kit can be used for earlier small-blocks with the two-piece seal.
- Big-block—externally balanced (PN 19329901). The kit is intended for Chevrolet Performance’s externally balanced 454 and 502 engines and includes an externally balanced flywheel.
- Big-block—internally balanced—and small-block with two-piece main seal (PN 19329902). This kit is intended for internally balanced Chevrolet Performance 427 and 572 engines, along with small-blocks using a two-piece main seal, and includes an internally balanced flywheel.
Additionally, separate bellhousing and clutch kits are available for all of the applications listed here, but the bottom line is it’s never been easier to adapt the modern performance balance of strength and efficiency of the Tremec six-speed for whatever restomod project you’re planning. See more details in the 2015 Chevrolet Performance catalog, which is available online at chevrolet.com/performance.