Although the above gains are all great, what really sets the new TCI 700-R4 apart from the GM 700-R4 is the TCI transmission's new Constant Pressure Valve Body. One of the GM 700-R4's key downfalls is the fact that it doesn't hold sufficient line pressure while cruising down the highway in overdrive at 1,800 rpm; in fact, the line pressure can be as low as 90 psi, which means the clutches are slipping ever so slightly all the time. Another problem area is making sure the GM 700-R4's T.V. cable, which determines internal line pressure and part throttle shifting, is set dead on. Unfortunately, to adjust the T.V. cable right where it needs to be requires some skill, and when the cable is improperly set, it will result in a transmission meltdown. TCI has found a way to avoid all this by designing the new Constant Pressure Valve Body to maintain at least 100 psi of line pressure at idle and 150 to over 200 when accelerating or cruising, the adequate amount of pressure at all times. The constant pressure avoids common transmission destruction, and although the transmission still requires a T.V. cable, the Constant Pressure Valve Body provides more freedom when setting part throttle shift points, upshift, and downshift timing. Line pressure settings are always at sufficient pressure at all times. That also means you won't find yourself encountering a low line pressure condition.
The TCI 700-R4's other main advantage is the lockup converter, which runs off vacuum provided by the intake manifold vacuum line, as well as a 12-volt source when the key is on. When hooked up, the lockup converter is good for another 200-rpm drop.
For now, TCI is only offering the new Constant Pressure Valve Body in their 700-R4 trannys, but due to the performance and driveability benefits they have seen in the 700-R4, plans are in the works to expand the lineup. Eventually, the TCI 200R and Ford AOD, both plagued with problems similar to the 700R, will include the new valve body. Until then, we decided to get our hands on one of the new 700-R4 transmissions to swap out the existing GM 700-R4 in John Barkley's square-body Chevy.
 The trans cooler lines need...  The trans cooler lines need to be removed as well, but first, John removed the dipstick on the trans for better access to the lines. From there, he released the T.V. cable hookup at the throttle linkage on the manifold. |
 There are three bolts that...  There are three bolts that bolt the torque converter to the flexplate. John began by removing the first accessible bolt,... |
 ...then he turned the engine...  ...then he turned the engine over by hand with a breaker bar to expose the remaining two bolts. |
 The last step was to unbolt...  The last step was to unbolt the six bolts that hold the trans bellhousing to the block. John then slowly dropped the tranny down, making sure nothing was hung up. He was sure to secure the torque converter from sliding off. |