Overdrive transmissions have been around since the 1930s, but for some reason, during the heyday of muscle cars they were nowhere to be found. Sure, gas was cheaper, but with big powerful engines and steep rear gears being the norm, if there was ever a time that an extra gear would have made sense, it was then.

It's not that we're getting soft; it's just that spinning the engine harder than it needs is bad on all fronts. Basically stated, an overdrive transmission is any gearbox, automatic or manual, that has a final gear ratio numerically lower than 1:1, typically in the .78 to .50 range. The main benefit is reduced engine rpm—which not only significantly improves fuel economy, but an overdrive also decreases engine wear thanks to slower piston, bearing, and valvetrain speeds. Those reduced speeds also reduce heat in the driveline, which leads to long-lasting components and lubricants. High rpm is always the enemy of longevity. Hand in hand with reduced rpm comes reduced interior sound levels, which is guaranteed to make long trips more pleasant. Just ask anyone who's taken a long road trip in a hot rod built for acceleration. They'll either sing the praises of their overdrive trans, or tell you that it's the next install on the list.

Thankfully, the aftermarket has come on strong with overdrives that can handle all the grunt, torque, and abuse hot rodders can dish out, and made it easy with complete swap kits to make it easy. Transmissions are kind of a black art to most hot rodders. We may understand basically how they work, but we'd rather not be the ones sitting at a table surrounded by clutch packs and gears. And when it comes to handling power reliably for many years, it's usually best left to the true experts. What we really need to know is where we can trust our money to deliver a product that just flat out works.

To help you find the source for your overdrive upgrade, we pulled together transmissions and swap kits from the companies we know and trust. Whether you want to keep your original trans, put in a beefed-up new automatic overdrive, or convert an auto to manual or vice versa, these are the folks to call to get more gears in your ride!


American Powertrain

Five-Speed Manual Early Mustang

American Powertrain sought to create the most complete, well-researched kits for the popular Tremec TKO five-speed manual, with a focus on making the least amount of permanent modifications. For some kits, including the popular early Mustang, the square TKO housing receives what American Powertrain refers to as Case Streamlining to aid fitment and reduce necessary modification and/or cutting. These kits include a mid-shift kit with shift knob (original four-speed shift position), a seamless DOM driveshaft assembly (race balanced with solid U-joints), cryogenically hardened steel driveshaft slip yoke, poly trans mount, stainless steel pilot bearing, reverse light harness, speedometer conversion (mechanical or electronic), hardware, and instructions.

Available Kits:

'55-57 Chevy Car or Truck
'67-92 Camaro/Firebird
'56-82 Corvette
'58-'64 GM B-body
'62-72 GM X-body
'63-72 C10 Truck
'64-72 Chevelle
'68-72 BOP A-body
'65-72 GM B-body
'67-68 Cougar
'64-71 Fairlane, Falcon/Comet and Early Fairlane through 1963
All Torino/Galaxie
'67-76 Mopar A-Body
'62-74 Mopar B-Body
'70-74 Mopar E-Body

Six-Speed Manual
First-Gen Camaro/Firebird

Based on Tremec's T56 Magnums six-speed, American Powertrain has created the Pro Touring kit for '67-69 Camaros and Firebirds that includes just about everything needed to get six gears in an early F-body. The kit includes AP a White Lightning shifter mechanism with white AP six-speed shifter knob (original four-speed shift position), DOM aluminum driveshaft assembly (race balanced with solid U-joints), X-Factor crossmember, stainless steel pilot bearing, reverse light harness, modular reverse lockout harness, speedometer conversion (mechanical or electronic), transmission hump, hardware, instructions, and a close- or wide-ratio Tremec Magnum six-speed.

Available Kits:

'55-57 Chevy Car or Truck
'67-81 Camaro/Firebird
'56-82 Corvette
'58-64 B-body
'62-67 X-body
'63-72 C10 Truck
'64-72 A-body
'68-72 BOP A-body
'65-72 B-body
'68-72 X-body
'64-'13 Mustang
'67-68 Cougar
'64-71 Fairlane
All Torino/Galaxie

Source:

American Powertrain
931-646-4836
www.AmericanPowertrain.com


GBodyParts.com

Four-Speed Automatic
200-4R Stage 3

GBodyParts.com builds some of the most serious 200-4Rs out there. They have a Stage 1 and Stage 2 for lower power levels, but the Stage 3 is the big daddy. Rated up to 1,000 hp and 850 lb-ft of torque, the Stage 3 is the ultimate 200-4R for big-block, nitrous, or turbo cars. Using only the best cores, GBodyParts loads in all brand new parts with some serious upgrades including hardened stator, billet anchor pin, EA high-pressure regulator valve and spring, EA high-rpm pump priming spring, billet pump rings, tensioned Teflon sealing rings, EA extra-large billet servo, EA billet forward clutch drum, EA billet input shaft, EA billet overdrive planetary, EA billet overdrive ring gear, EA billet 6061 direct and forward pistons, billet rotor and slide assembly, HD roller low center support, HD roller low/rev ring gear, seven-clutch max duty direct pack (multi parallel), five-clutch forward pack, three-clutch overdrive pack, high-static low-reverse clutch, carbon-fiber wide band, recalibrated valvebody for firm shifts, and a sheet aluminum pan with bottom-mounted sump. You also get a two-year warranty.

Source:

GBodyParts
252-825-3293
www.GBodyParts.com