Volume III, Issue 9, Page 12

Hot How-To Swap: Turbo 350 to 700R4

At first, the idea of adding an overdrive feature was novel to hot rodders and enthusiasts, another piece of must-have equipment for the complete car. The original equipment manufacturers were way ahead of hot rodders in this instance, and have been putting them in production vehicles for more than 25 years. See, Detroit actually did learn something from the first of the fuel debacles in 1973. Hence, a ready market for the hop-up guys before there even was a market, corporate average fuel economy (CAFE) notwithstanding. The advent and press coverage of popular over-the-road gatherings such as the Hot Rod Power Tour stressed the importance of this auxiliary gear and in today’s gas–crunch climate overdriven top gears have become mandatory equipment.

Preliminary Precautions
Although possible to do in your driveway, the operation will go much easier with the car on a lift. If you must do this operation on the ground, support the vehicle with jack stands at all four corners. These transmissions are very heavy, hold many quarts of fluid, and wiggle room is scant, so regardless of your method, you must use a proper transmission jack to support the case and to move it back and forth. Before you begin, disconnect the battery, the TV (throttle valve) cable from the carburetor or EFI and the hold-down bracket, remove the distributor cap, and place the shift lever in Neutral. Raise the car. NOTE: Powerglide, Turbo 350 and Turbo 400 transmissions use vacuum control to perform the upshift. The 700R4, 200-4R, etc, do this via the cable-operated throttle valve (TV).

You can delete some of the transmission mass (prox. 25 pounds) immediately by dropping the pan and draining the fluid. In any case, have the correct plastic plug or a spare yoke to cap the output shaft to keep the fluid from draining out once the driveshaft has been extracted. Have a bucket ready. Now you are ready to begin.

NOTE: This is an excerpt from Cartech’s “GM Automatic Overdrive Transmission Builder’s and Swapper’s Guide” that will be released in October. Please click on the link here for more details.

Disconnect the shift linkage from the transmission and move it aside or tie it out of the way. If the shifter is an aftermarket item, the procedure is still the same.

Using a 7/16 wrench, remove the U-bolts holding the driveshaft universal joint to the differential yoke. Be careful to retain the bearing cups and keep the roller bearings intact.