Manual & Automatic Transmissions

How to choose a transmission for a swap or rebuild

Match three things before anything else: the bellhousing pattern of the engine, the torque the engine makes, and how the transmission will be shifted and controlled. Gear ratios come next, chosen together with your axle ratio and tire size.

Manual transmissions: torque rating and ratios

Torque capacity separates the common TREMEC aftermarket gearboxes. TREMEC rates the T-5 for up to 300 lb-ft, the TKX 5-speed for 600 lb-ft, and the Magnum 6-speed for 700 lb-ft. Leave margin above your engine's torque figure, especially with sticky tires or forced induction. Within a model, check the ratio set: the Magnum family is offered with a 2.66 or 2.97 first gear and double overdrive, and TKX versions are listed as close or wide ratio. The TR-4050 is a truck gearbox with a six-bolt power take-off.

What a manual swap needs

TREMEC says that in most cases replacing a factory transmission with one of its units requires changes to the driveshaft, crossmember, and clutch and bellhousing arrangement. Two installation steps matter most: TREMEC specifies a maximum bellhousing runout of .005 in., checked with a dial indicator, and stresses keeping the original driveline angle to avoid vibration and damage. TREMEC Magnum units ship without oil. Install kits in this department are sold for specific engines, so match the kit to your block, such as small block Chevy before or after 1986, LS, or small block Ford.

Automatics: hydraulic or electronic

Older GM automatics are controlled hydraulically. The TH350 and TH400 are three-speeds without overdrive; the 700R4 adds a 0.70 overdrive and depends on a correctly adjusted throttle valve (TV) cable. TCI calls proper TV cable adjustment essential for shift points and transmission life. Electronic units such as the 4L60E, 4L80E and 6L80E are shifted by a computer, so a swap needs a transmission controller; TCI recommends its EZ-TCU for standard operation of its 4L60E-based 4X, and Chevrolet Performance's engine and transmission packages include a transmission controller. The two-speed Powerglide is common in drag racing; TCI lists OEM first-gear ratios of 1.76 and 1.82.

Torque converters

Stall speed should suit the camshaft, gearing and use. A lock-up converter lets you use a higher stall at launch and lower cruise rpm on the highway, as TCI describes for its 4X. TCI advises having any used converter professionally flushed and inspected, and never installing a converter of unknown specifications or origin.

Race and remanufactured units

Circle track race transmissions from makers such as Bert, Brinn, Falcon and Winters are sold for specific racing classes and are listed by rear main seal type, so confirm both your rules and your block. Remanufactured automatics are replacement units; match them to your vehicle's original transmission and application.

Choosing the engine as well? See crate engines, including Chevrolet and Ford packages, or send fitment questions through contact.