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)

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."


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