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 0 Comment(s)

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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