As the technology in Pontiac’s engines progressed over the years, so did its transmissions. Back in the glory days, manual boxes featured linkage-actuated clutches and three or four forward gears. The internals were simple and rugged, and the shifting a bit notchy, but they got the job done and provided a grin that can only be derived from manually slamming the shifter into the next gear.
Over the course of the next 30 years, three- and four-speeds gave way to the five-speed and six-speed transmissions with internal rail shifters and built-in reverse lockouts. The T56 six-speed was standard in Fourth-Gen Trans Ams and Formulas and late-model GTOs. It’s not uncommon to hear about a six-speed late-model LS car getting upper 20s in fuel economy or holding lots of rwhp with stock guts from Tremec, while still being a smooth shifter.
“How is this possible?” you ask. Let’s take a look inside a Tremec T56, more specifically an M12 out of an ’05 GTO.
This variant was shared by the other GM powerhouses of the day—the Corvette Z06 and Cadillac CTS-V—and has some upgrades inside straight from the Tremec factory that make it better than previous T56 transmissions. Out of the box, the synchronizer sleeves feature stepped teeth to make engagement feel lighter and more positive. The synchronizers also utilize high-density-carbon blocker rings and reverse synchronizers. Additionally, the M12 uses a one-piece countershaft, which is stronger than a two-piece.
[1] Because of the easy access...
[1] Because of the easy access to the adapter-to-bellhousing bolts, we decided to remove our transmission here. We also noticed a crack in our bellhousing, so we took extra precautions with the removal using our transmission jack.
Still, with all these upgrades, our intense downshifting and track duty combined with a few shifts during wheelspin resulted in the loss of Second gear. In our case, it was worn fork pads that prevented us from smoothly selecting Second gear and eventually caused the synchronizer to fail. We called Gray Fredrick from American Powertrain and explained our situation. We were soon provided with the correct package for our Goat.
With our heads and cam GTO used primarily for road-course racing and on the street, there was no need to go crazy with upgrades and break the bank. According to Gray, there are affordable solutions for each power hike you make with your Pontiac.
[2] With the transmission case removed, we discovered that the crack was actually a clean break (upper left), as the piece around the alignment dowel went along for the ride as we backed the transmission out and lowered it away from the car.
[3] The fluid was drained...
[3] The fluid was drained prior to disassembly.
“Unlike most packages out there, we include a vehicle-weight rating with ours because we can confidently say they can hold the claimed power level at the listed vehicle weight,” he says. “It’s easy to say a transmission can hold 500 hp, but is that 500-horse transmission going to hold the power in a car weighing 4,000 or more pounds? In our experience, it won’t.”
Because of these established power ratings, it was easy for Gray to suggest the Level 2 package, which is rated for a 495 lb-ft constant-torque load.
[4] Complete disassembly is...
[4] Complete disassembly is required to extricate the parts to send to American Powertrain, and is best done by a professional, like Greg Lovell.
[5] With the trans torn down,...
[5] With the trans torn down, we learned that our mainshaft received some heavy wear. Gray suggested we go ahead and replace it with a new one from Tremec to be treated rather than reuse this one.
[6] Gray took this photo before...
[6] Gray took this photo before sending our transmission pieces back to us. In it, you will find the parts you should expect to send out from your transmission. While you will receive the mainshaft partially assembled, your mechanic will still have some bearings to press-in, snap rings, and other assorted parts to assemble.
“This package is going to be the solution for 80-percent or more of enthusiasts out there. While peak loads and shock loads can climb well above this on the dyno, not many engines run these kinds of numbers on a sustained basis.
[7] This diagram illustrates...
[7] This diagram illustrates how the mainshaft and the input shaft and gear assemblies attach to the front adapter plate.
“The ratings are based on a 3,600-pound curb weight and street-legal radials. It covers the typical upgrades you would want, such as bronze fork pads and shims, but takes it a step further with cryo and REM treatments.” Those last two upgrades Gray mentioned add a new level of strength to the internal components.
You may have already heard the word cryogenic or cryo thrown around the hot rod industry for some time. It can increase strength up to 30 percent without affecting tolerances.
[8] This is the front mainshaft...
[8] This is the front mainshaft assembly, featuring (left to right) the Second and Third gears, synchronizer, gear blocker, synchronizer, gear blocker, First gear, and a tapered bearing. The billet synchronizer keys are considerably stronger than the factory parts, and are considered a necessity for high-performance applications.
[9] The First/Second shift...
[9] The First/Second shift fork was cryo-treated to increase strength.
[10] The Third/Fourth shift...
[10] The Third/Fourth shift fork is darker, as it’s not made from aluminum like the First/Second. This is because the 2-3 shift is usually the most violent and it’s not uncommon for the aluminum forks found in earlier variations of the T56 to actually break. Our GTO came from the factory with this stronger steel shift fork.
[11] Gray wanted us to point...
[11] Gray wanted us to point out the discoloration on the input shaft. This is normal and occurs after the treatment process.
[12] This is the Fifth/Sixth...
[12] This is the Fifth/Sixth driven gear. These are the overdrive gears that help these modern transmissions achieve excellent highway mileage with their 0.84:1 and 0.56:1 ratios, respectively.
[13] After receiving the parts...
[13] After receiving the parts from American Powertrain, Anti Venom’s Greg Lovell carefully taps the races for the countershaft and input shaft bearings into the front adapter.
[14] With the front adapter...
[14] With the front adapter elevated, the cryo- and REM-treated input shaft with its pressed-in tapered bearing is lowered into place.
American Powertrain’s cryogenic treatment consists of slowly reducing the temperature of the parts to -300 degrees F using liquid nitrogen, and then holding that temperature for 12 hours. This process relieves stresses and minute fissures in the part by refining the structure of the metal, resulting in a more uniform material. Strength and wear resistance are improved.
The rate at which the temperature of the part returns to normal also contributes to its attributes. According to American Powertrain, the quicker the part is returned to normal temperature after the process is completed, the better.
[15] After Greg taps the bearing...
[15] After Greg taps the bearing onto the front of the mainshaft using a properly sized traditional socket, the mainshaft is mated to the backside of the input shaft on the adapter.
REM treatment follows cryo and is a process that fills the minute imperfections that occur naturally in the gear’s surface. By filling and polishing these minuscule valleys and inconsistencies, fluid pressure requirement and friction are reduced across the gear face, and durability and corrosion resistance are enhanced. According to Gray, this translates into reduced temperatures, noise, and parasitic loss—which is good.
With the package chosen, we disassembled our broken transmission and sent the parts to American Powertrain to have them treated and put back together with parts included in the Level 2 package. Greg Lovell at Anti Venom handled the disassembly and reassembly.
[16] Next the countershaft was installed after its tapered bearing was pressed on (shown behind the bottle). Maintaining optimal lubrication of the parts—especially the bearings—during the assembly process is crucial. Greg uses Pennzoil ATF.
[17] The shift rails were...
[17] The shift rails were installed next. These will house the shift forks that we sent out to American Powertain for the treatment process. This is where a professional installer comes in handy to line things up correctly. Everything will be installed in neutral to keep the Third/Fourth shift rail from engaging.
While Anti Venom is mostly known for its high-end builds and performance installs, Greg has been rebuilding transmissions since he was a teenager and most of those high-horse cars that roll off out of his garage feature a trans he rebuilt. Even with the great “how-to’s” out there, it’s always best to seek out professional expertise when dealing with an expensive manual transmission.
Please keep in mind that this is not a step-by-step trans teardown and rebuild story, as space would simply not allow it. Instead, we cover most of the highlights of the process and discuss the upgrades.
[18] Greg slides on the new...
[18] Greg slides on the new bronze fork pads. From the factory, these pads are made of a nylon that tends to wear and distort under the stress of performance driving. Once they have worn out, it can make it extremely difficult to shift—as was the case with our GTO. As the first point of contact after a shift is made, this simple upgrade can increase transmission longevity and improve shifting feel.
[19] This is what 80,000 miles...
[19] This is what 80,000 miles of performance driving can do to the stock fork pads. These units were all showing signs of intense wear, and certainly contributed to the shifting issues we were experiencing.
[20] Here we see what the...
[20] Here we see what the transmission looks like after installing the mainshaft, countershaft, and First/Second and Third/Fourth shift forks.
Level 2 M12 T56 transmission
495 lb-ft constant-load torque rating
Price: $995
The Level 2 kit includes:
Bronze fork pads for 1st, 2nd, 3rd, 4th, 5th, 6th, and Reverse
Billet synchronizer keys and spring kit for 3rd/4th synchronizer assembly
Cryo treatment of 1st-4th gears, shift forks, and sliders
Call tag to pickup parts from customer (within continental U.S.) to have cryo-treatment performed
The following parts will need to be removed and boxed for American Powertrain to Call Tag for this upgrade:
1st/2nd/3rd/4th gears and their input shaft
Countershaft (lower gear in gearbox, also known as cluster)
Sliders, not hubs, for 1st-2nd and 3rd-4th
Shift forks (no rails) for 1st-2nd and 3rd-4th
[21] Next, Greg lines up the...
[21] Next, Greg lines up the parts for the Fifth/Sixth driven gear and Reverse gear to be installed. First the case has to be installed, so he cleans the gasket mating surface.
[22] This closeup of the shift-fork...
[22] This closeup of the shift-fork rail assembly gives you an idea of its complexity, which can be overwhelming for a first timer. Greg tells us that everything will only be happy going together one way, so it may take some trial and error before moving onto the next step. A generous bead of high-temperature silicone is applied to the perimeter of the front adapter on the raised surface where it will come in contact with the case.
[23] Greg slowly lowers the...
[23] Greg slowly lowers the case onto the front adapter. This can be tricky, as the parts resting in place underneath will want to move around with the slightest touch. After a few attempts, he is finally able to align it correctly to the dowels and keep the front assembly together. He then tightens the case-to-adaptor bolts in a crisscross pattern to 26 ft-lb.
[24] Finally, the Fifth/Sixth...
[24] Finally, the Fifth/Sixth gear driven is lowered onto the main shaft with Sixth gear aligned. This is followed by the reverse shift fork, which is held in place with a snap ring, and the reverse speed gear assembly.
[25] Carefully, the transmission...
[25] Carefully, the transmission extension housing is lowered into place and guided in with the alignment dowels. This houses the countershaft extension bearing, as well as the reverse idler shaft, gears, and bracket. The bracket bolts are treated to Loctite and torqued to 18 ft-lb. The extension housing bolts receive 26 ft-lb and the same silicone process as the front adapter. (There are many other steps and procedures to dismantling and rebuilding the T56—too numerous to cover in a single story.)
[26] Here’s the completed...
[26] Here’s the completed trans, ready for reinstallation. The process of removing the transmission from our car took a couple hours on a lift. Greg had it apart in less than an hour with our parts bagged and tagged to be sent out for treatment. The turnaround time from American Powertrain is usually one to two weeks, depending on the package.
[27] As per Gray’s suggestion,...
[27] As per Gray’s suggestion, instead of tracking down another expensive OEM bellhousing, we took the opportunity to upgrade to this sharp SFI-approved QuickTime bellhousing that is offered with some of American Powertrain’s kits. Unfortunately, our large 1.875-primary headers created some clearance issues with the slightly wider bellhousing. This required Greg to remove some material on the driver side, which negated its SFI rating.
[28] This is the ACT Street...
[28] This is the ACT Street Disc (PN GM9-HDSS)—an entry-level clutch, which offers a holding capacity rating of 745 lb-ft while offering smooth actuation. The kit comes with a heavy-duty pressure plate, a sprung hub organic disc, and a 26-spline alignment tool. It retails for around $488.
[29] We combined the clutch...
[29] We combined the clutch kit with the SFI-approved Prolite Xact Flywheel (PN 600585; $350), which has a terrifically low weight of 14.7 pounds. The combo has proven after-track use and extended street driving to maintain its user-friendliness and easy operation with crisp throttle response. We also installed a new hydraulic slave cylinder (PN SACHS PN SH6414; $87) that actuates the clutch and pilot bearing (ACDelco PN CT1078; $14) from Rock Auto. It took Greg a little over two hours to reassemble the trans, and another couple hours to put it back into the GTO. With its upgraded parts and Pennzoil Synchromesh Manual Transmission Fluid in it, the trans shifts buttery smooth and there is a positive feel to each gear selection. It’s the perfect build for our demands and makes the car more enjoyable to drive every day.