True Connections

This month we continue our discussion of transmission swaps with the installation of a TH700R4. Lately this has proven to be a popular transmission swap due to the increasing availability of cores and the fact that it is a 4spd automatic overdrive transmission. The higher 4th gear will allow the use of a lower rearend gear for increased acceleration without adversely effecting drivability at cruising speeds. The TH700R4 does require a few special pieces that are made only for that transmission. They include the flex plate, dust cover, dipstick & filler tube, kickdown, or TV cable, and the torque converter lockup kit. Once the flexplate is installed according to the manufacturer’s specifications, the transmission with the converter can be mounted up to the engine. The stock crossmember can be used by simply relocating it back along the frame, similar to the installation of a TH400 which we discussed a few issues ago. The next step would be to have your driveshaft shortened, & luckily the yoke used in the powerglide and TH350 is the same as what you will use for the TH700R4. If you are using a column shifter you can use the same linkage that was used with the TH350 or TH400 transmissions. The stock floor shifter will require some modifications, fortunately there are kits available to help. The TH700R4 will use a floor shift cable similar to the TH350 & TH400 but the detents on the shifter itself will need to be replaced due to the extra gear in the transmission. The final jobs left are to install the TV cable & torque converter lock up kit, both of which are available through aftermarket manufacturers. We contacted Mogi Transmissions in Riverside, Ca. to find out a little more about setting up these items and we came to the conclusion that for the average car builder this process it is best left to a qualified transmission shop. The reason for this is that the setup needs to be perfect, otherwise you could cause severe damage to your transmission.

There are two other things to consider before you go out and purchase a TH700R4. One, is the amount of horsepower you intend to use in front of it. It is well known that a TH700R4 will be hard pressed to withstand anything above 500hp. We have heard of many a 700R falling by the wayside when mounted to a high horsepower motor. The other thing to consider is the gearing of your vehicle. If you drop in a TH700R4 with your stock 3.08 gears, the engine RPM’s will be much to low to effectively cruise at freeway speeds. The ratio we prefer to use with a 700R would be a 3.73 rear gear. Of course there are other factors involved but at speeds of 60-65 mph & 3.73’s, engine RPM’s will be around 2000, which will be great on your mileage. Next issue we’ll discuss installation of body mount bushings.