Bob's Resource Website (2007)

(Transmission Conversion Facts)

Transmission / Driveshaft FAQ

Transmission Selection:

sources are from the net, with modifications as required

Transmission conversion: Most people feel the 3 best choices are the Chevy Turbo 350, Turbo 400, and Turbo 700-R4. 

The Turbo 350 is very suitable; is abundant and most easily incorporated. 

The (short shaft) Turbo 400 is the best choice for performance considerations. It is more robust than the T350 but is harder to find and more expensive. It makes driveshaft fabrication more difficult, but it is the way to go if one has the need for speed (but not MPG). Note: be aware that "Chevy" style TH-400 with a short tailpiece are getting rare. 

The Turbo 700-R4 is a good choice* due to the higher rear-end gear ratios on older cars. On a Stude with 3.31 rear end gears, the overdrive T700-R4 will drop engine speed from 2500 RPM to 1750 RPM at 60 MPH. Highway fuel economy will increase about 30% and general wear-and-tear on the engine components will be reduced. Avoid pre-1985 versions of these transmissions, as they have known reliability problems, unless they are salvaged from Police Cars or they are remanufactured for heavy duty use . Also, a switch is required to operate the lock-up feature of the torque converter in high gear-- failure to do so will cause damage** to the transmission. B&M sells this Power Switch for about $40 and it includes wiring instructions. It is also possible to have a hydraulic version of this valve installed within the transmission. 

Note: When searching for a 700-R4 for use in a conversion, remove the torque converter, and look on the front plate inside the bell-housing for the casting number. Get one with the last three digits being 732. This ensures an 87 or newer unit with the best of GMs updates.