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Classic Chevy 5 Speed Transmission Insight - CHP Insider

Jeff Mortenson Of Classic Motorsports Group Tells All There Is To Know About Swapping An Overdrive Stick Into Your Classic Chevy

Stephen Kim Aug 1, 2009
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So what if the guy in the other lane is putting the holeshot on you with his 5,000-stall converter? Truth be told, outside of the top 1 percent of power-shifting studs out there, an automatic is the quickest way down the track. However, for many hot rodders the thought of becoming a stab-and-steer jockey isn't particularly appealing. Whether it's for apex clipping on the road course, streetability improvements around town, hearing loss prevention on the freeway, or simply having a dirty good time on the street, fully experiencing the visceral rush of going WOT requires a clutch pedal beneath your left foot and a shift lever in your right hand.

That's why folks like Jeff Mortenson of Classic Motorsports Group work hard to make swapping five- and six-speed sticks into your musclecar painless. CMG offers complete Tremec TKO and T56 conversion kits for just about every classic Chevy out there. To throw some pointers your way, we spent a day at Mortenson's shop and learned how to help you trade in that old-school Muncie or Powerglide for a modern overdrive manual. Thanks to CMG, it is much easier than you might think.

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Company Background
As is often the case, Classic Motorsports Group was founded by enthusiasts who discovered a void in the marketplace through firsthand wrenching experience. As Jeff Mortenson embarked on a Tremec five-speed swap for his Chevy musclecar several years ago, he noticed that no one offered a complete turnkey conversion kit. After dealing with the headache and expense of tracking down parts from several manufacturers and waiting for weeks whenever custom components had to be ordered, he recognized the need for bundled conversion kits and started Classic Motorsports Group with business partners Scott Lindquist and Jim Goodlad.

The concept of packaging everything for a five- or six-speed swap--including the trans, crossmember, shifter, clutch assembly, driveshaft, and hydraulics--under one convenient part number has really caught on. "It's really just a hobby gone wild. It started out as a weekend project in my garage, and just a few years later we became the largest distributor for Tremec in the country," Mortenson quips. "As demand picked up, we moved into several platforms such as the Camaro, Nova, Chevelle, Impala, and Corvette. Before we knew it, we had our own in-house R&D department, fab shop, and warehouse. I've always had a passion for doing things the right way, and it shows in our products."

Easy Overdrives
The perceived difficulty of upgrading to modern overdrive manual trans may seem intimidating, but Mortenson says that it's the product of common misconceptions and assures us that the swaps are actually straightforward. "Whether you're running a small-block, a big-block, or an LS motor, our goal is to provide a bolt-in transmission solution for your car that requires little or no modifications, achieves stock shifter positioning within your stock center console, and retains a factory appearance. Some applications require cutting the floorboard, but with the templates and patch panels we include with our kits, it's not difficult at all. Our shifters come up in the stock location, and it's not even necessary to switch to buckets if you have a bench-seat car. We currently have turnkey kits for '67-81 Camaros, '64-72 Chevelles, '58-88 Corvettes, Tri-Fives, '62-74 Novas, and '60-69 Impalas

Cutting Tunnels
In certain applications, such as Chevelles and Chevy IIs, the only way to make room for a TKO is to cut the trans tunnel. Fortunately this process isn't as difficult as it may seem, and Mortenson has some helpful tips to guide you along. "A lot of people are scared about cutting their tunnel, but it's more of a mental block than a physical block. After tracing around the template supplied with our kit, use a cutoff wheel or plasma cutter and slowly start cutting the tunnel," Mortenson explains. "Our patch panel is designed to require as small a hole as possible while still providing the necessary clearance for the Tremec trans. Since the panel will be covered by carpet, even if you're not the best welder it's not a big deal. After welding the panel into place and reinstalling the carpet and center console, the interior will look stock."

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Turnkey Approach
By nature, hot rodders are resourceful people always looking to stretch a buck. Even if you're particularly adept at scouring salvage yards and eBay, it's tough to beat the convenience of a turnkey five- or six-speed swap. "If you can get the same components we offer in our kits for less money, I'd be very surprised. At the end of the day, scrounging up parts from multiple sources will probably cost you more," Mortenson explains. "At Classic Motorsports Group, we want to be a one-stop shop for people who value their time and want to do things right the first time. In the unlikely scenario where you could do it cheaper by piecing a swap yourself, it will take much longer, cause more headaches, and may require some custom fabrication."

CMG's Deluxe kits--designed for factory four-speed cars--include either a Tremec TKO or a T56 trans, a custom crossmember, a driveshaft, a speedometer cable, a trans mount, and a pilot bearing. To that, its Elite kits--designed for automatic-to-stick conversions--add a bellhousing, a flywheel, and a clutch assembly. A clutch pedal, a Hurst shifter, and hydraulic assemblies are optional.

T56 Magnum
"Although most people opt for a TKO trans, CMG also offers T56 six-speeds for hot rodders who need an additional overdrive ratio or just want to impress their friends with an extra gear. The big news, however, is the upcoming T56 Magnum. An updated version of the T56, this is the same transmission used in new Camaros and Corvettes. Revisions include larger input and output shafts, larger and stronger gears, an improved heat treatment process, a stronger case, double- and triple-cone synchronizers, laser-welded dog teeth, stronger shift forks, and shorter throws. The result is an astounding 700 lb-ft torque capacity, which is more than enough for everything outside of full-blown racecars.

In the past, rebuilding a T56 to handle big loads was an expensive proposition, but the Magnum only costs a couple hundred dollars more than a standard T56. Unlike a Jerico or a Lenco, a Magnum is very much a street-friendly transmission. For added versatility, the Magnum has multiple shifter locations and mechanical and electric speedometer pickups and is compatible with both cable- and hydraulically actuated clutches."

Upon installation, a fresh manual trans can feel a bit tight, but Mortenson says that this is completely normal. A combination of fresh synchronizers, gears, and blocker rings, the extra effort required when shifting gears will loosen up very quickly. "First fill the trans up with 2.65 quarts of GM Sychromesh fluid, and take it easy for the first 500 miles," explains Mortenson. "That means no hard shifts or clutch dump. The trans will shift tight for the first 50-60 miles, but it will free up very nicely after that. The fluid is designed to last the life of the trans, so there's no need to drain it after the break-in period."

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Light-duty Tremec five-speeds such as the T5 have earned an underwhelming reputation with enthusiasts, but the TKO is a different animal. Essentially evolutions of the TR-3550, the TKO 500 and TKO 600 are extremely stout gearboxes rated at 500 and 600 lb-ft of torque, respectively. Compared to the TR-3550, which was designed to serve behind meager stock-output V-8s, TKOs feature larger gears, tapered roller bearings, a beefed-up case, an internal three-rail shift system with cast iron forks, 4615 alloy steel gears and shafts, a stronger single-piece countershaft, and a short-throw billet shifter.

"Since it was designed specifically with hot rod applications in mind, the TKO has provisions for eight shifter locations, three crossmember mounting locations, and electric and mechanical speedometer pickups," Mortenson explains. "The TKO 500 has a deep 3.27:1 First gear, while the TKO 600 has a 2.87:1 First, which accounts for the difference in torque capacity. Enthusiasts can choose between a 0.64:1 and a 0.82:1 overdrive on the TKO 600, while the TKO 500 has a 0.68:1 Fifth gear. Considering its flexibility, strength, and low cost it is not surprising that the TKO is the most popular aftermarket Tremec overdrive by a large margin."

Custom Crossmembers
Having the right crossmember can literally make or break your five- or six-speed swap. To ensure a proper driveline angle and trans positioning, CMG includes a custom crossmember with all its kits. "The crossmember mounting pads on the Tremec TKO and Magnum transmissions are located farther back than on the stock four-speeds and automatic transmissions found in older Chevys. Without a custom crossmember, the customer would have to fabricate his own unit, which can be time-consuming and difficult to properly build," says Mortenson "Our crossmembers are direct bolt-in units constructed from 0.120-inch 1020 carbon steel tubing as found in NASCAR and NHRA approved rollbars. Unlike less expensive and weaker box design crossmembers, CMG's mandrel bent, tubular design provides maximum torsional strength and rigidity, are lighter in weight, and are compact in size for maximum exhaust clearance. Each crossmember utilizes thick CNC-cut flanges, precision TIG and MIG welding, and black powdercoating for a beautiful finish."

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Shifter Location
Thanks to the various shifter locations of the TKO, it's often possible to achieve proper shifter placement within the stock console while using the factory Tremec shifter. However, in cars such as first- and second-gen Camaros, the Tremec shifter sits too far to the right. Furthermore, in Novas and '64-67 Chevelles, the Tremec shifter won't work at all. The solution is the offset Hurst Blackjack shifter, which allows for perfect positioning inside the factory center console. "Using the Blackjack shifter eliminates the need to modify the car, center console, or transmission itself," says Mortenson. "It's built from 4340 billet steel and 6061 T-6 billet aluminum, utilizes a Delrin pivot ball, and works as a direct bolt-in replacement shifter. CMG has a complete line of Blackjack shifters for the TKO and T56 Magnum transmissions for proper shifter placement in Camaros, Chevelles, and Novas that have center consoles. Again due to our relationship with Hurst, the Blackjack shifter is an exclusive offering from Classic Motorsports Group."

Shared Resources
In late 2007 CMG was acquired by B&M, which also owns Hurst. Mergers like this are common and usually of little consequence to the consumer, but being part of the B&M/Hurst family has greatly improved the types of products we are now able to market. With access to our parent company's resources and engineers, we can reach more people and offer exclusive products. For instance, CMG has just released a reproduction of the original Hurst round-style shifter handle found in '68 and '69 Camaros. This shifter handle exactly replicates the factory shifter's bends, angles, and height. Since CMG is part of the Hurst family, we can use the original Hurst logo on the shifter, making this an exclusive part only available from CMG. For the '68-69 Camaro owner who wants that original look, this shifter handle is a great choice.

Corvette Caveats
The Corvette has always been more of a sports car than a traditional muscle car, and as such its compact dimensions mean that space is at a premium when it comes to swapping in a modern manual trans. Mortenson says that it's not uncommon to have just 1/8 inch of clearance between the top of the trans case and the tunnel in these cars, and removing the factory tunnel insulation may be necessary. "In order to make swapping a TKO in a '58-82 Corvette as easy as possible, CMG machines the trans case for tunnel clearance," Mortenson explains. "We also install a Hurst Sidewinder shifter that mounts to the side of the tailshaft housing, which in turn positions it perfectly in the stock location. Furthermore, the rearend mounting points on these cars can bend over time, which throws off the U-joint angle on the driveshaft. To compensate for this, we include shims that can be installed on top of the crossmember to raise the trans."

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A critical link in any trans swap is the bellhousing, and CMG offers units designed for just about every conceivable configuration, whether it's a small-block,a big-block, or an LS motor. For mega-power applications, the company has a complete line of SFI-approved steel scattershields. For vehicles where maintaining a stock appearance is a priority, CMG manufactures a reproduction of the popular GM "621" bellhousing for both TKO and T56 transmissions. "These bellhousings feature a low-pressure injected titanium-aluminum alloy construction and are precision built to within 0.005 inch of run-out," says Mortenson. "So not only do they look just like the factory bellhousing, they're much stronger as well. Each unit is double-checked for proper register bore alignment and parallelism prior to shipping, which is very important when installing a TKO transmission."

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"Developing a new five- or six-speed swap kit isn't particularly complicated, but it's a time-consuming process that requires lots of patience. First, we test-fit parts that we know will fit in all models of a vehicle platform, such as the bellhousing, clutch, and flywheel. The next step is mounting the trans at the correct height to achieve a proper driveline angle. If our desired driveline angle creates interference between the trans and the floor, we modify the floor for clearance. After the trans is bolted in, we can determine if a stock or an aftermarket Hurst Blackjack shifter is necessary to position the shifter in the stock location. After that, a prototype crossmember is fabricated with the goal of duplicating the correct driveline angle we achieved earlier in the R&D process while still providing enough room for the exhaust.

"As for the hydraulics, most of it is a bolt-in affair. The most difficult part is figuring out where to mount the master cylinder. We make our own custom brackets for Chevelles and Camaros in order to position it properly on the firewall where it's out of the way of other components.

"With the exception of our Corvette kits, no mods are performed to the exterior of any of the transmissions that we sell. That way, if you want to pull your trans out and sell it later on down the road, it will fit in any car because it hasn't been modified."

In the Works
Due to the tall 0.50:1 Sixth gear ratio and limited shifter locations of the standard T56, CMG only offers it in '67-74 Camaros and '68-74 Novas. However, CMG will soon be offering six-speed swaps for every Chevy musclecar where a TKO swap was once the only option. "The main drawback of the standard T56 is that it took a lot of work to relocate the shifter to the locations necessary in most Chevy musclecars. Plus, most of them had a lower torque capacity than the TKO," Mortenson explains. "With the new T56 Magnum, all that's changed since it accommodates several shifter locations, and it is rated at 700 lb-ft. In conjunction with the Hurst Blackjack shifter, we'll now be able to offset the shifter to place it in the stock location. We are working hard to have our T56 Magnum kits readily available within the next few months."

Sticky Pedals
Owners of many late-model GMs with factory six-speeds often complain of hydraulic issues, such as sticky clutch pedals and improper clutch disengagement. Since this is an undesirable characteristic in any application, CMG made sure to eradicate the problem in its six-speed kits. "The problem isn't necessarily a product of the T56 itself, but actually the result of GM's hydraulic system," says Mortenson. "In order to smooth out clutch engagement, GM inserted a restrictor valve into the fluid supply line. Many racers have found that drilling out this valve reduces the tendency for the clutch pedal to stick on the floor. Our solution is to use a Tilton master cylinder, which prevents this issue from surfacing in the first place."

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Clutch Actuation
"Although Tremec transmissions work with a stock mechanical linkage, CMG has a complete bolt-in hydraulic clutch setup that will convert your car to a modern hydraulic system. In the past, mechanical linkages were preferred in high-horsepower applications due to the fact that they could handle greater pressure plate clamping loads. However, this has changed with modern advances in clutch technology. For example, CMG offers an optional LUK 11.5-inch clutch rated at 600 hp that's compatible with our hydraulic system. Our hydraulic setup includes a throwout bearing, a master cylinder, a remote mount reservoir, and all fluid lines and hardware.

"The most important part of the conversion is the master cylinder firewall mount bracket. The stock firewall is too thin to properly mount a clutch master cylinder, and our bracket is designed to provide a solid foundation for it. Additionally, the bracket positions the master cylinder pushrod at the correct geometric angle for proper pedal feel."


Classic Motorsports Group



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