Get In Gear With A TCI 700-R4 – Tech
Although invisible to the eye, sometimes the biggest gains are the ones that seem plain and mundane. When most people think about a custom classic truck, they ponder flashy paint, wheel and tire combos, and custom body mods. But what good is all that exterior hoopla if the drivetrain underneath limits the truck to side-street commutes and freeway speeds that refute Sammy Hagar’s “I Can’t Drive 55″ argument? Oftentimes, poor driveability can be directly linked to the transmission, which is why TCI Automotive designed a new 700-R4 tranny that is sure to kick things up a notch.
Whether you’re simply trying to step up from a Powerglide, Turbo 350, Turbo 400, or just replacing a tired 700-R4, the new TCI 700-R4 transmission is an improvement above them all, in more than just one way. But for starters, we’ll go with replacing a Powerglide, Turbo 350 or 400. Due to the fact that the 700-R4 transmission is equipped with four gears, including overdrive, gear ratios will be adjusted for better take-offs, and perhaps most importantly, highway cruising. In terms of taking off from a dead stop, the 700-R4 clocks in with a 3.07 first gear, as opposed to a 2.48 in a T400 or a 2.52 in a T350. The 700-R4’s 3.07 gear is basically the equivalent of a 20 percent lower rearend gear, which directly results in better 60-foot times. As for cruising, a 700-R4 is equipped with a .67 overdrive that gives you a 33 percent higher rearend gear. To put it another way, if you have a 3.73 rear gear and a Turbo 400, the switch to a 700 gives you a low gear like a 4.11 and highway cruising like a 2.56 rear gear.
If all those crunched numbers and figures are flying across the top of your dome, then let’s slow things down and put them into laymen’s terms. Let’s say your truck currently runs a Turbo 350 or 400 and it cruises down the freeway at 4,000 rpm. If you upgraded to a 700-R4, the .67 overdrive would drop that rpm figure to around 2,800 rpm at the same speed! As a result of the lower rpm, your truck would no longer scream and shake like an overcaffeinated Robin Williams goin’ down the freeway. And as a result of that, you’d be able to hear the local radio station play the same seven songs over and over and your friends talk about the glory days back on the football field.
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.
Photo Gallery: TCI 700-R4 Transmission – Custom Classic Truck



