Pontiac’s transmission offerings for 1964–1974 GTOs were similar to the transmissions offered in other Pontiac and GM models. Transmissions were sourced from Muncie, Saginaw, GM’s Hydra-Matic Division, and even Dearborn (Ford). In addition to 3- and 4-speed manual transmissions, Pontiac also offered 2- and 3-speed automatic transmissions.
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When the GTO arrived in 1964, three manual transmissions were available: the standard Muncie 3-speed manual, an optional wide-ratio Muncie M-20 4-speed, and a close-ratio Muncie M-21 4-speed available only with 3.90:1 gears installed at the factory or with dealer-installed 4.33:1 gears. (There has been speculation as to whether the close-ratio 4-speed was actually installed in any 1964 GTOs, even though it is listed as available.) All manual transmissions used a 10.4-inch clutch featuring a single dry-friction plate, bent-finger diaphragm spring, and a 2,350-pound spring-loaded pressure plate. The clutch assembly was housed in an aluminum bellhousing, which also mounted the transmission.
The sole automatic transmission choice was an upgraded version of the 2-speed Super Turbine 300 that was available in the Tempest and LeMans series. The transmission was mated to the 215 inline six (I6) and the 326 and 389 V-8s in the General Motors A- and B-Body cars. This 2-speed transmission was slotted into various models in the Buick, Oldsmobile, and Pontiac lines. The ST300 has a complex multi-angle torque converter and front and rear clutch packs. A planetary gear set, front band, and a clutch pack were dedicated for manual low gear and reverse. The transmission weighed 152 pounds, and it shifted from low to high gear at highway speeds. Though often mistaken for the Chevrolet Powerglide automatic, it is in fact a different transmission. Both transmissions have a certain level of similarity, but they are different designs.
Compared to other transmissions offered by competing manufacturers, such as Ford’s C4 3-speed automatic and the clearly superior Chrysler 727 TorqueFlite, the Super Turbine 300 transmission sent performance enthusiasts straight to the manual transmission choices. History has treated the Super Turbine 300 very kindly and because of its design and wide gear ratio, but not many owners opt to rebuild the Super Turbine 300. Instead, many GTO owners install a Muncie or Turbo 400 if using a period-correct transmission, particularly with non-numbers-matching cars.
The transmission offerings were revised in 1965. The Muncie 3-speed manual was replaced with a Ford-built Dearborn Toploader 3-speed. This transmission is the strongest manual transmission ever put in a GTO and required a new transmission bellhousing to mount it. This transmission lineup continued unchanged through 1966.
The manual transmission lineup remained unchanged for 1967, but the performance-sapping Super Turbine 300 was finally dropped from the GTO lineup with the introduction of the legendary M-40 Turbo 400 HydraMatic. An extremely strong and durable 3-speed automatic, it was introduced in the 1964 Cadillacs and in the full-size offerings of other GM brands the following year. It featured gear ratios of 2.48, 1.48, and 1.00:1. The Turbo 400 is still regarded as one of the greatest transmissions ever developed, and even nearly half a century after its initial release, GM is still building the 4L85-E, a computer-controlled overdrive version of this transmission.
These basic transmission offerings were retained without changes other than coding until the 1970 model year. It was then that two significant changes were made. First, the introduction of the 455 HO V-8 required the substitution of a larger 11-inch clutch with an effective 2,750-pound pressure plate to handle the additional torque output of the long-stroke engine. It was similar in design to the standard 10.4-inch version. Only the 455 engines received the larger clutch.
The second major change was the retiring of the Dearborn Toploader 3-speed manual transmission. The new base transmission was a Muncie heavy-duty 3-speed manual transmission that was related to the Muncie 4speeds.
The 1971 transmissions were the same as from previous year, except that the M-21 close-ratio 4-speed transmission was replaced with a stronger version of the Muncie close-ratio gearbox the famous M-22 “Rock Crusher” 4-speed. It was the strongest 4-speed manual ever installed in a GTO. This lineup remained unchanged in 1972.
In the interest of fuel economy and emissions, some more restrictive changes were made in 1973. The close ratio M-22 was dropped, leaving the wide-ratio M-20 as the only 4-speed transmission. Additionally, the optional 455 4-barrel V-8 was available only with the M-40 Turbo 400 automatic.
With the GTO moving from the A-Body platform to the X-Body, the transmission choices mirrored those available in the rest of the Ventura series and continued to use the 10.4- inch clutch system. The Muncie manual transmissions were replaced with lighter-duty Saginaw transmissions. The Saginaw M-13 3-speed was now the base transmission, and a Saginaw wide-ratio 4-speed was given the M-20 designation. The Turbo 400 used in previous years was replaced with the more compact M-38 Turbo 350 automatic.
Rebuild or Replace?
The transmission in your GTO may not be the original one from the factory. Many failed in the line of duty and were replaced under warranty or were swapped out later.
If your car is a numbers-matching example and you are doing a concours-style restoration, then retention and rebuilding of the original transmission is a priority, especially if it is a manual transmission, which not only has the application code, but also the VIN of the car stamped on it. As long as the case is in good condition, everything inside can be replaced without detracting from the car’s value or hindering authenticity with regards to judging. Cars equipped with automatic transmissions are not judged as stringently as cars fitted with manual tranmissions, though the application code must be correct for the car to be considered numbers matching.
If your car does not have its original transmission, it is still worth restoring and certainly it’s less of an issue if the GTO is to become a regular driver. If the transmission you have is in good working order or is at least rebuildable, you can save quite a bit of money working with it. For example, if your GTO has a later BorgWarner Super T-10 out of a Trans Am, or your 1965 Goat has a Turbo 350 instead of the 2-speed automatic, it really isn’t a problem and if you don’t want to search out a correct transmission that might actually hurt its drivability, it is perfectly acceptable to work with what you have.
Turbo Hydra-Matic 400
The Turbo Hydra-Matic is one of most prolific and highly regarded automatic transmissions of all time and certainly the GTO helped further its performance record. The Turbo 400 offered a breakthrough in performance from its predecessors and became favored among racers and hot rodders. Whether on the street or track, drivers could run larger and stickier tires and put the transmission under more stress, and it kept coming back for more. The Turbo 400 transmitted the power from 400 and 455 GTOs, but this legendary transmission also handled the shifting duties for many Buicks and Cadillacs.
A huge aftermarket offers every component for this transmission including torque converters, gear sets, gaskets, seals and bearings, so this transmission can be set up for virtually any application. You can find a wide range of high-performance parts, such as flexplates, planetary parts, torque converters, bellhousings, cases, and valve bodies. The Turbo 400 can also be rebuilt at home, but there isn’t time or space to cover all the specifics here. However, the entire rebuilding process of the Turbo 400 is covered in How to Rebuild and Modify GM Turbo 400 Transmissions by Cliff Ruggles. A myriad of businesses offer every kind of performance part for the Turbo 400. Among the many reputable shops is TCI Transmissions and Cliff’s High Performance.
Automatic Transmission Upgrades
When you need to upgrade your transmission, you can improve the one you have for better performance or you can swap in a newer, more modern unit for the advantages of better technology, strength, and an overdrive gear.
Most transmission manufacturers and remanufacturers offer shift-improvement kits, high-performance clutch packs, high-strength bands, and other components to increase transmission performance and durability. Additionally, a higher-stall converter can also be added without causing a visually incorrect situation. All of these upgrades can add up to a very noticeable performance gain. If you are restoring a numbers-matching GTO, this is a normal and accepted regimen that won’t cause any deductions in points.
If you are not restoring a numbers-matching GTO, or not otherwise concerned with originality, you have many more options. Replacement transmissions are as close as your local rebuilder or a larger company, such as TCI, B&M, or other manufacturers. They are also stocked by Summit, Jegs, and other larger performance parts retailers. You can have a transmission custom-built to your specifications and price range, often cheaper than doing it yourself if you figure in the cost of the specialized tools needed to do the job. If you already have the skills and tools to rebuild a transmission yourself, great. Otherwise, it is perfectly acceptable to buy one ready to go. Again, if you are inexperienced in the area of transmission rebuilding, have a reputable builder prepare your transmission.
Super Turbine 300 to Turbo 350
If you have a 1964–1966 GTO that came with a 2-speed Super Turbine 300 automatic and aren’t doing a concours restoration, a time-honored, inexpensive, and very easy swap is to replace that substandard 2-speed slushbox with a vastly superior Turbo 350 automatic out of a 1968 or newer Pontiac A- or F-Body. While not quite as beefy as the larger Turbo 400 in stock form, it does have less parasitic drag and it swaps into these early GTOs with minimal effort, using the existing crossmember and driveshaft without alteration. It is an option well worth looking into. If strength becomes an issue with your combination, beefed-up versions take up to 700 hp, so you’re not really losing anything by using one.
Another option that makes a lot of sense with street-driven GTOs is to use an automatic overdrive transmission. Even if your car does not have aggressive gears, it is still advantageous from fuel economy, engine longevity, and highway comfort standpoints to have your Pontiac V-8 merrily loafing at 1,500 to 1,800 rpm at common highway speeds. If you have experienced driving a vintage GTO for sustained periods at 65 to 75 mph, you already know that without an overdrive, it tends to rev higher than necessary, negatively impacting gas mileage. If you’re used to later-model cars, it’s more than a little annoying; it’s like you’re waiting for the overdrive and lockup to kick in, yet it never does. Using an automatic overdrive transmission often increases the mileage to such an extent that it actually becomes a viable cross-country hauler. It is not unheard of to crack into the low- 20-mpg range with an overdrive-equipped GTO, even with 400 or more horsepower.
Conversely, the use of an overdrive allows you to retain a modicum of driveability when using aggressive gears. With an overdrive of .70, a 3.90 becomes a 2.73:1, a 4.11 gear runs like a 2.87:1, and a 4.33 performs like a 3.03:1 final drive, adding a great deal of civility to a car with steep gears from the factory or for a more radical street/strip combination.
If you are going for the ideal combination of fit and beefiness in a factory transmission, look for the 2004R out of a 1986–1987 Buick Grand National or a 1989 Trans Am turbo. Though rare, they can be found from used parts vendors, eBay, racingjunk.com, or even craigslist. org, if you’re lucky. These transmissions are desirable for two reasons. First, the Buick V-6 used in those cars and the Pontiac V-8 use the same bolt pattern, so adapting is not necessary. Second, they are strengthened to handle the power output of the turbocharged V6s, which were actually as strong as most 1960s-era big-blocks. Many aftermarket versions are even further strengthened. If you strike out finding one of those fairly rare units, most automatic transmission builders can build you one that is beefed up to handle just about any power level.
Another option is to use the more common 700R4, used on many performance-oriented GM products from the late 1980s and early 1990s. Avoid units built before 1987, as they are substantially weaker than their later counterparts. They are easily upgraded with high-strength components from the later-model, computer controlled version, the 4T65-E, which was offered in LT1 and LS1 powered cars. The 700R4 requires an adapter plate to mate it to the Pontiac V-8 and the crossmember must be modified or replaced with an aftermarket unit designed for the swap. The length of the driveshaft also needs to be modified.
Last, I would be remiss if I didn’t mention the 4L80-E, the late-model, computer-controlled version of the Turbo 400 automatic. This is a more complicated and more expensive alternative to the 2004R and the 700R4, but it does offer the advantage of a stand-alone computer that is not tied to any engine controls. The twist is that the 4L80-E was offered behind Diesel engines in Chevy and GMC pickups. Because of the Diesel engine’s lack of an ignition system, that combination needed a transmission controller that wasn’t dependent on any engine electronics. Once this controller is reprogrammed with shift patterns suited to a carbureted V-8, this transmission becomes a very attractive choice, though it is more expensive than the others and requires an adapter and driveshaft mods to work in a GTO chassis. It may also require some transmission tunnel mods to fit, as it is physically a very large transmission.
Owners of manual-transmission GTOs enjoy a great deal of aftermarket support, with rebuilding and exchange services available for Muncie, Saginaw, and Dearborn transmissions on both local and nationals levels. Additionally, several companies restore Hurst shifters. Rather than recommend specific companies to do these operations, this is a good area to get the opinions and recommendations of local club members. The reasons are twofold. One, it is likely that you will find someone right in your local club chapter or your area who can do a great job for not a lot of money, or may be willing to trade out the job for parts or other non-cash consideration. The other reason is that the cast of characters is constantly changing, especially in the Hurst shifter rebuilding world. Some of the best guys only do a few each year or are not consistently available. Hurst rebuilds shifters as well, so that is an option.
The regular productions codes identify an M-20, M-21, and M-22. Of the regular production codes, one particular Muncie 4-speed type appears. A properly set up M-22 Rock Crusher transmits up to 700 hp, so this stout transmission is a wise choice for high-performance applications as well as authenticity. But that is not a definitive method for positively identifying the transmission.
On the edge of the main case is a number stamping that identifies the Muncie gearbox as well as state the year and month it was made. For Muncies, the serial number starts with the letter P. The serial number sequence from 1963 to 1966 started with the month and then the day of the month. For August 16, 1963, the serial number is P0816.
However, from 1967–1968 the year designation was first in the serial number sequence followed by the letter for the particular month. The third digit represents the month. The first month in the year is A, so the third month in the year is C. The third day in the month is represented as 03 So, this gearbox reads P7C03.
Several businesses offer high-quality rebuild kits for the Muncie 4-speed transmissions, including 5speeds.com and T&B Transmission & Gear. These businesses offer a full range of gears, synchros, gaskets, mainshaft bearings, and even a full case, so you can build a Muncie 4-speed from the ground up or you can rebuild one from your GTO. T&B and 5speeds.com offers the M-22 Rock Crusher Supercase. T&B offers a complete Muncie 4-speed and it features the new Masiero Italian gearsets, Muncie Supercase, super tailhousing, iron midplate, and roller bearing sidecover. Medatronics Corporation at 5speeds.com offers M-22 complete transmission with the finest components from Autogear. Like the T&B M-22, the Medatronics sold M-22 exclusively uses Masiero gears. When buying a rebuild kit or an entire gearbox, be sure to buy these components from a reputable source. Some of the Muncie components you see Online are made to substandard tolerances and are of inexpensive materials. You put yourself at risk of failure if you build your gearbox with these components.
Muncie 4-Speed Disassembly
Step-1: Place Shift Shafts in Forward Position
To begin the rebuild, use a 9/16-inch wrench to remove the four bolts that secure the clutch gear bearing retainer. The bearing-retainer nut, which is a left-hand thread, follows both shift shafts on the case cover. The shift shafts are placed in the forward position, locking the transmission into gear. Midwest Transmission Supply offers a J-tool (PN WT297-W) to facilitate the job. It retails for about $40. (Photo Courtesy General Motors. Used with Permission, GM Media Archive)
Step-2: Remove Case Cover
Before removing the case-cover assembly, place the transmission into second gear by leaving the rear shift shaft (on the case cover) in the forward position and moving the front shaft to the center. Remove all seven case-cover retaining bolts with a 1/2-inch wrench, lift the assembly away from the unit, and set it aside. (Photo Courtesy General Motors. Used with Permission, GM Media Archive)
Step-3: Remove Speedometer Gear
Remove the speedometer gear fitting using a 7/16-inch wrench, which is required to take off its retaining bolt. Pull it out of the case and examine it. Make sure the nylon gear is in good condition and is not damaged. Set it aside for the re-assembly process. (Photo Courtesy Rocky Rotella)
Step-4: Remove Reverse Gear Lock Pin
Look down inside the case at the mainshaft gear and the counter gear. If there has been a gear box failure and it’s locked up, you can see the damage to the gear sets. Use a 3/16-inch-diameter punch to drive the reverse-gear lock pin upward and out of the rear extension (tailshaft). (Photo Courtesy Rocky Rotella)
Step-5: Place Transmission in Neutral
After removing the case cover, place the transmission in neutral by manually positioning the rear synchronizer sleeve so the teeth of all four bronze synchronizer rings are visible. (Photo Courtesy Rocky Rotella)
Step-6: Separate Main Case and Tail Case
Thread a bolt into the reverse shift shaft and pull the reverse shift shaft outward about 1/2 inch, freeing the reverse shift fork from the reverse gear. The rear extension is attached to the main case assembly by six bolts, all of which must be removed with either a 9/16- or 5/8-inch wrench. A few blows from a soft mallet separates the main case assembly and the tail case, which is rotated away and set aside. (Photo Courtesy Rocky Rotella)
Step-7: Remove Mainshaft from Case
Extract the rear-bearing retainer and mainshaft assembly, including the reverse idler gear, from the main case. Though still intact here, the main drive gearshaft (or input shaft) simply pulls away from the mainshaft, but most likely remains in the main case, where it can be gently tapped out of its main bearing and into the main case. It can also be tapped outward, along with its bearing, and be removed as a unit. (Photo Courtesy Rocky Rotella)
Step-8: Remove Steel Drive Gear
The speedometer’s steel drive gear is pressed onto the mainshaft and must be pulled off for complete disassembly. Use a bearing separator tool (available from Mac Tools and other sources) to complete the task. Slide the mainshaft reverse gear off the mainshaft and pull the reverse idler shaft straight out. (Photo Courtesy Rocky Rotella)
Step-9: Inspect Mainshaft Gears
The mainshaft and gear cluster are seen here. Inspect the gears for chipping, excessive wear, or other visible imperfections. It is a lot easier to replace any necessary parts at this time, than take the cluster out of the case a second time. (Photo Courtesy Rocky Rotella)
Step-10: Remove Rear Bearing Snap Ring
To disassemble the mainshaft, use a pair of external snap-ring pliers to remove the rear-bearing retainer snap ring located on the rear end of the mainshaft. (Photo Courtesy Rocky Rotella)
Step-11: Press Mainshaft through Bearing
Insert the mainshaft assembly into a hydraulic press; while supporting the rear-bearing retainer, spread the snap ring, and press the mainshaft through the rear bearing, separating the two. The procedure is the same as the one illustrated here from the service manual. (Photo Courtesy General Motors. Used with Permission, GM Media Archive)
Step-12: Disassemble Mainshaft
Using snap-ring pliers and working front to rear, remove the front snap ring that retains the third-and fourth-gear synchronizer sleeve and third gear. (The synchronizer sleeves and hubs are matched pairs, so be sure to keep them oriented correctly.) (Photo Courtesy Rocky Rotella)
Step-13: Disassemble Mainshaft (Continued)
While supporting second gear, insert the mainshaft into the hydraulic press. Applying pressure from the rear, remove the second gear, the first- and second-gear synchronizer hub, and the first gear to gain access to the second-gear synchronizer-block ring. (Photo Courtesy General Motors. Used with Permission, GM Media Archive)
Step-14: Disassemble Mainshaft (Continued)
Using a 3/4-inch-diameter metal dowel and a hydraulic press, remove the countershaft gear pin by applying pressure from front to rear. This allows removal of the countershaft gear, its 112 roller bearings, and its thrust washers, as well as the front reverse idler gear and its thrust washers. Set all parts into a parts washer for a thorough cleaning. The main drive gear and its bearing were already removed from the main case. (Photo Courtesy Rocky Rotella)
Step-15: Decode Transmission ID
Here is an example of the coding found on a manual transmission: P9E01A. It breaks down as follows: P=Muncie Plant; 9=1969; E=May; 01=1st day of the month; A=M-20 wide-ratio. (Photo Courtesy Rocky Rotella)
Step-16: Decode Transmission ID
The original vehicle’s VIN is typically stamped on the top of the main case in Muncie applications and, in this particular case, it’s broken down as follows: 2=Pontiac Motor Division; 9=1969; R=Arlington, Texas, assembly plant; 175134=vehicle identification number. This unit appears to be from a 1969 Pontiac A-Body, most likely from a GTO, but possibly from a Tempest, Custom S, or LeMans. (Photo Courtesy Rocky Rotella)
Muncie 4-Speed Assembly
Step-1: Press On Second Gear
After visually inspecting all the parts that could be reused for signs of excessive wear or fatigue, cut a suitable length of 1¾-inch-diameter steel pipe to help press the second gear, its bronze synchronizer-block ring, and the first- and second-gear synchronizer clutch assembly (synchronizer hub and sliding sleeve) onto the mainshaft. (Retain the shifting keys on the synchronizer hub with heavy bearing grease.) Once that is completed, install the retaining springs. (Photo Courtesy Rocky Rotella)
Step-2: Press On First Gear
Continue with the first-gear synchronizer-block ring and first gear. Use lightweight engine oil for lubrication. (Photo Courtesy Rocky Rotella)
Step-3: Install New Rear Bearing
Tap a new rear bearing in place using a 15⁄8-inch-diameter pipe and then install the rear-bearing retainer. Spread the front snap ring, sliding it over the rear of the mainshaft and fully seating it against first gear. Select a rear bearing retainer snap ring that reduces clearance between the snap ring and the rear-bearing face to a maximum of .005 inch. This limits mainshaft endplay when under load, much like an engine’s thrust bearing. (Photo Courtesy Rocky Rotella)
Step-4: Install Third and Fourth Gear Synchro
The third gear and the third- and fourth-gear synchronizer clutch assembly and snap ring follow. Set the completed mainshaft assembly aside for the time being while the main case is attended to. (Photo Courtesy Rocky Rotella)
Step-5: Install Countershaft Roller Bearings
Use a liberal amount of heavy bearing grease to retain the countershaft gear’s roller bearings and bearing washers. This procedure includes loading a .050-inch washer in one end, followed by a row of 28 roller bearings, another washer, 28 more roller bearings, and the last washer. (Photo Courtesy Rocky Rotella)
Step-6: Install Countershaft Roller Bearings
Perform the same steps on the countershaft’s opposite end until a total of 112 roller bearings are installed. (Photo Courtesy Rocky Rotella)
Step-7: Place Countershaft Gear in Main Case
Set the countershaft gear and thrust washers into the main case. Using a hydraulic press, gently press the countershaft pin into the case from the rear. (Photo Courtesy Rocky Rotella)
Step-8: Insert Pin in Main Case
The pin should be flush with the front of the case, and its stepped portion should face downward to clear the rear bearing support. Check the countershaft gear endplay with a dial indicator if old thrust washers are reused. It shouldn’t exceed .025 inch. If it does, replace the washers. (Photo Courtesy Rocky Rotella)
Step-9: Install Roller Bearings in Mainshaft
In this diagram from the service manual, heavy bearing grease is used to retain 17 new roller bearings and a retaining cage into the main drive gear cavity before installing the unit onto the nose of the mainshaft. (Photo Courtesy General Motors. Used with Permission, GM Media Archive)
Step-10: Install New Gasket
Install a new gasket onto the front of the rear-bearing support, placing the fourth-gear synchronizing ring on the main drive gear, sliding the 3-4 synchronizing clutch sleeve forward into the fourth-speed detent position, and insert the entire mainshaft assembly into the main case. This positions the main-bearing retainer so that the guide pin in it aligns with the hole in the case. Tap it into place. (Photo Courtesy Rocky Rotella)
Step-11: Install Front Reverse Idler Gear
With the unit loosely assembled, install the front reverse idler gear (its tanged thrust washer into the main case) and insert the rear reverse idler gear through the rear-bearing support. (Photo Courtesy Rocky Rotella)
Step-12: Orient Front Reverse Idler Gear
This photo was taken prior to the installation of the front reverse idler gear on the mainshaft assembly. It shows the correct orientation of the front reverse idler gear’s forward thrust washer. (Photo Courtesy Rocky Rotella)
Step-13: Insert Reverse Idler Gear
Insert the rear reverse idler gear thrust washer and reverse idler shaft. Note the position of the shaft’s lock pin; it corresponds with a notch in the rear extension. (Photo Courtesy Rocky Rotella)
Step-14: Install Reverse Shift Shaft Seal and Parts
During disassembly, you removed the reverse shift fork and drove the reverse shift shaft into the extension housing (the reverse shifter shaft detent ball and spring fell out). Replace the reverse shift shaft seal before reinstalling the spring-and-detent-ball assembly back into the housing (shown is the assembled housing). With a small flat-blade screwdriver, reinstall the reverse shift shaft and shift fork, then remove the existing bushing in the rear extension and tap the replacement into place with a race driver. Next, install the rear extension oil seal. (Photo Courtesy General Motors. Used with Permission, GM Media Archive)
Step-15: Install Reverse Gear and Speedometer Drive Gear
Slide the reverse gear onto the mainshaft and drive the speedometer drive gear into place using a length of steel pipe. According to the Pontiac service manual, the drive gear’s proper location is roughly 6.15 inches from the rear of the shaft. Also install the rear extension gasket at this time. (Photo Courtesy Rocky Rotella)
Step-16: Install Tail Case
Pulling the reverse shifter shaft outward, slide the rear extension over the mainshaft while aligning all the internal components. Give the six retaining bolts a coating of blue thread locker and tighten them to the suggested torque spec. Apply torque evenly to the case during tightening. The upper three bolts receive 20 ft-lbs of torque, and the lower three receive 30 ft-lbs. (Photo Courtesy Rocky Rotella)
Step-17: Install Reverse Shaft and Speedometer Gear Fitting
Install the reverse shift shaft lock-pin and speedometer gear fitting. Use a new O-ring to ensure proper sealing. (Photo Courtesy Rocky Rotella)
Step-18: Install Roller Bearing
Install a new roller bearing and snap ring onto the main drive gear. (Photo Courtesy Rocky Rotella)
Step-19: Install Case Cover
With the shift shafts and shift forks in place, slide the third-and-fourth gear synchronizer sleeve into the neutral position while leaving the first- and second-assembly in the forward position. From there, position the case-cover gasket and lower the case cover into place. (Photo Courtesy Rocky Rotella)
Step-20: Install Case Cover Bolts
Tighten the case cover’s seven retaining bolts to 18 ft-lbs of torque using a crisscross pattern. (Photo Courtesy Rocky Rotella)
Step-21: Install Bearing-Retainer Nut
After sliding both mainshaft synchronizer sleeves forward to lock the transmission into opposing gears, thread the bearing-retainer nut onto the main drive gear. Although using the correct tool (shown earlier) is preferable, a flat blade screwdriver and hammer, or a pipe wrench, can also be used to gently walk it around the main drive gear to tighten. Remember, it’s left-hand thread, and the correct torque spec is 40 ft-lbs. The nut can also be staked with the corresponding holes in the main drive gear to securely lock it into place. (Photo Courtesy Rocky Rotella)
Step-22: Install Clutch Gear Bearing Retainer
Install a new gasket on the clutch gear bearing retainer before sliding it over the main drive gear. Note the machined hole points toward the bottom. This ensures that the retainer’s internal oil drain is positioned correctly. Apply thread locker to the four retaining bolts and tighten each to 20 ft-lbs of torque. (Photo Courtesy Rocky Rotella)
Step-23: Install Seals on Case Cover
The forward shift forks and shifter shafts have been removed from the case cover during disassembly. Use a ballpeen hammer and a socket that matches the diameter of the new seals. Then tap the new seals into place on the shift fork cover. (Photo Courtesy Rocky Rotella)
If you are looking for a fifth or sixth gear for your GTO, there are two main options available. The first is the Tremec 5-speed transmission, which is an aftermarket transmission designed to be a bolt-in replacement for a 3- or 4speed GM transmission. It bolts up to a factory bellhousing and is the same overall length as a factory transmission, so this transmission is a viable candidate for a street-driven GTO.
The other option is the Tremec T-56 6-speed manual transmission. This is an expensive upgrade for a GTO, or any A-Body for that matter. The most desirable version is from the Dodge Viper and most aftermarket versions use the Viper internals for higher strength. The T-56 should be considered only for a Pro-Touring style of build, as it requires extensive transmission tunnel modification. Really, a new tunnel needs to be fabricated and truth be told, you’re cutting the car up pretty well at this point. Add a custom bellhousing/ scattershield, as well as a new crossmember, and you’re talking about a big-ticket upgrade.
Step-24: Fill Case with Fluid
There are some transmission builders who feel that synthetic lubricant was never intended for use with vintage manual transmissions. Conventional lubricants, such as this 75W-90 product from Valvoline, seem to be the choice of those professionals. The M-20 Muncie’s capacity is 2.5 pints. (Photo Courtesy Rocky Rotella)
Adapting this transmission to a traditional Pontiac V-8 is possible, but if you are seriously considering it, please re evaluate your restoration mission statement, as this is a pretty serious investment and the course of your project will change significantly.
A T-56 becomes a much more viable alternative if you are re-powering your GTO with a GM LS-series engine, like the original LS1 used in the 1998– 2002 Firebird/Camaro or the later LS2 used in the 2005–2006 GTO. You can buy the engine and transmission together, along with the computer system, and do it as a complete conversion. I don’t mean to upset any traditional Pontiac V-8 fans who would be against a corporate V-8 transplant, but this information is included in the interest of providing a complete description of the options available. If the idea of an LS-powered GTO is appealing to you, there are other books out there that describe this path more completely.