Offering great strength and performance on the track while also enabling great highway fuel economy, it’s little wonder the TREMEC Magnum six-speed transmission is the gearbox of choice for many builders these days. Pro Touring pioneer Mark Stielow has used it exclusively on his last several Camaro projects and is going with it again with his latest build, dubbed Gunner.
Based on the design of the well-regarded T-56 transmission, the Magnum uses the “guts” of the TREMEC TR-6060, with its gearbox found in late-model performance vehicles such as the fifth- and sixth-gen Camaro, C6 Corvette, and Cadillac CTS-V. Simply put, it picks up where the T-56 left off, with elements designed to stand up to the kind of performance generated by, say, the 650hp Camaro ZL1.
“The T-56 was great for power levels of the vehicles it was matched with,” said Don Walsh, Sr., founder of transmission specialist D&D Performance in suburban Detroit. “As time, technology, and performance capability marched on, so did the need for a stronger transmission, and that’s where the TR-6060 and Magnum came in.”
The Magnum’s greater strength comes from larger and stronger components compared to the T-56. First gear, for example, is 22 percent thicker in the Magnum than in the T-56. But for all its built-in strength, there are a couple of elements that could still be stronger. We’re talking about the blocker rings—also known as synchronizer rings—and the shift fork pads. For virtually indestructible performance, Walsh recommends replacing the standard brass blocker rings with carbon-faced or total carbon units and swapping the original plastic fork pads with brass ones.
More than the potential of breaking the components, heat is a persistent threat, particularly for cars that see regular track time. “If you’re not running a trans cooler, it’s very easy to heat up the transmission fluid to 200 degrees F,” says Walsh. “That can melt the fork pads and add to the wear of the blocker rings.”
Stielow plans to put Gunner on the track the moment the last bolts are tightened and the final wiring harness is plugged in, so bulletproofing it is a top priority. The only rub to making these upgrades is they require the transmission to be completely disassembled.
“You really want to do it before the transmission starts shifting ‘funny,’ because by that time it’s too late,” says Walsh. “It’s cheap insurance and you’ll probably never have to touch the transmission again.”
To be clear, these enhancements don’t increase the transmission’s torque capacity, but make it more durable. We followed along as D&D Performance’s Carlos Tumpkin tore down Stielow’s brand-new Magnum transmission and installed the new components. At Stielow’s request, the Sixth gear ratio was also changed from 0.63 to 0.50, to reduce rpm on the highway and stretch out the intervals between fill-ups.
At D&D, the upgraded blocker rings and shift fork pads cost $600 for parts and labor. Making changes to a brand-new, dry transmission was infinitely more convenient than tearing down a used gearbox. Think about that when you order your next Magnum. One more thing. It’s important to note that the accompanying photos and captions provide an overview of the steps involved and not every nut and bolt turned in the project. CHP
1. The teardown begins with the removal of the shifter assembly and the transmission’s tailshaft extension housing over the mainshaft (also known as the output shaft).
2. With the extension housing removed, the 5-6-Reverse shift rail comes out. It moves the shift fork that’s connected to the 5-6-Reverse synchronizer. The Magnum transmission has a separate shift rail for the 1-2-3-4 shift forks and synchronizers.
3. The speedometer gear comes next, along with a ball bearing that allows the removal of the roller bearing between the output shaft and the extension housing. After that, the Reverse gear pulls off the mainshaft.
4. Next, the 5-6-Reverse synchronizer assembly is removed from the mainshaft.
5. The 5-6 driven gear comes off the mainshaft next, and the process involves a long gear puller to clear the mainshaft. A tie-wrap at the bottom of the puller holds it to the gear.
6. The disassembly continues with the removal of the Reverse drive gear, which is located on the countershaft.
7. Digging further into the gearbox, the 5-6 synchronizer is removed and then the 5-6 hub itself.
8. After removing the fasteners that hold the shift lever guides in place, the transmission case is removed from the gearset.
9. Here, the 5-6-Reverse shift linkage is removed.
10. The 3-4 synchronizer is removed to allow the gears to be removed from the synchro hub.
11. A press is used to remove the individual gears from the synchro hub. Here, Third gear is being removed.
12. This is the all-carbon blocker ring assembly for the 1-2 synchronizer that D&D swaps into the assembly. The upgrades also include carbon-lined brass rings for the 3-4 and 5-6-Reverse synchros.
13. Here, the Sixth driven gear and bearing are pressed off the countershaft. The plate beneath the bottom gear (First) spreads the load under pressure to help remove everything conveniently as an assembly.
14. Changing the top-gear ratio involves swapping two gears: the larger drive gear (not shown) and the complementing, smaller driven gear (seen here). In this instance, the ratio was changed from 0.63 to 0.50 in order to reduce highway-cruising rpm.
15. The new blocking rings are soaked in ATF for about a half-hour prior to installation.
16. The new Sixth driven gear and complementing bearing are heated on a hot plate for a few minutes before being installed on the output shaft.
17. With the parts still hot, requiring a glove, the new Sixth driven gear and bearing are slipped onto the shaft without the need to press them into place.
18. After installing the blocker rings on the synchronizer, the 3-4 synchro hub is pressed back on to the mainshaft.
19. New bronze fork pads simply snap on in place of the original plastic pads—a simple yet highly effective upgrade that stands up to heat and cracking.
20. The mainshaft slides onto the input shaft. All the blocker rings have to be aligned perfectly to ensure proper operation.
21. One of the trickiest aspects of the assembly is indexing the shift levers on the 1-2-3-4 and the 5-6-Reverse rails. They’ve got to be lined up just so before the attachment screws can be fastened from the outside.
22. Wrapping up where the project began, the shifter assembly is reinstalled. The upgraded Magnum is now ready for lap after lap of gear-banging performance.
Back to Basics: How a Manual Transmission Works
When it comes to rowing the gears yourself, there are two basic types of manual transmissions: the sliding-gear type and the constant-mesh design. With a sliding-gear trans, nothing except the main driver gear and cluster gear turn when the transmission is in Neutral. Pushing the clutch pedal and moving the shifter engages the linkage and forks required to mesh the appropriate gears and get the vehicle moving. The design requires the driver to un-mesh one gear before meshing another, which could lead to gear clashing because the gears within the transmission all rotate at different speeds.
With a contemporary constant-mesh transmission, such as the TREMEC Magnum, all of the gears on the mainshaft continuously mesh with the cluster gears, because rather than being splined to the shaft, the gears freely rotate on it. All of the gear hubs are always turning, even when in Neutral.
Alongside each gear on the mainshaft is a dog clutch with a hub that is splined to the shaft and an outer ring that can slide over each gear. The mainshaft gear and the ring of the dog clutch each have a row of teeth. Moving the shift linkage moves the dog clutch against the adjacent mainshaft gear, causing the teeth to lock the gear to the mainshaft.
Finally, synchronizers are used to prevent gears from grinding or clashing during engagement. They push in one direction to lock a gear to the mainshaft and disengage that gear to engage another on the other side when pushed the other way.
There’s more to the components and the intricacies of the synchro action, but this brief summation should keep you in gear.
Photos by: Barry Kluczyk