When it comes to drag racing performance, your transmission is nearly as important as your engine. Sluggish and sloppy shifts rob power, thus killing e.t.’s. It can also make your Chevy a real buzzkill to drive around town. The first-glance solution is a new transmission, but that can be a strain on your wallet. The other, far more affordable solution is to do some minor surgery on the transmission you already have.
Modern overdrive transmissions have computers, but before that, transmissions had minimal electronics and were mechanically controlled by a valvebody. By changing some parts in the valvebody, your transmission—in this case a 700-R4—can be “reprogrammed” to have firmer, power-saving shifts. With the TCI Automotive Constant Pressure Valve Body kit you can also fix one big pain with the 700-R4 transmission: the TV cable. Yep, many a 700-R4 has been damaged by a poorly adjusted TV cable (used to set internal line pressure and part throttle shifting). The TCI system solves this potentially destructive scenario by adding parts that maintain adequate line pressure at all times. Yes, there’s still a TV cable, but getting it adjusted perfectly is no longer a gamble.
Since we were knee-deep in trans fluid, we also decided to add a lockup wiring kit to the install mix. This would allow us to either manually lock up the converter whenever we want or have it automatically lock up when cruising in Fourth gear. These two TCI kits, along with a more aggressive torque converter, should breathe new life into our previously sluggish 700-R4 and help the Nova it resides under, knock down some better times at the dragstrip.
1. This is what our 700-R4 looked like with the pan off. Our first task was to remove the large flat filter by pulling it straight up, and then toss it and the filter seal ring in the waste bin.
2. Doing this exposed our stock valvebody. Think of it as a mechanical computer that controls how and when the transmission shifts.
3. We then removed the 1-2 accumulator by removing the three bolts holding it in place. These bolts were kept separate from the others since they are specific to the accumulator. Also, notice the circular wear ring on the valvebody separator plate.
4. Next up was removing the auxiliary valvebody, making sure not to lose the stock check valve (arrow), since it will be reused.
5. The throttle pressure mechanism was then unbolted (two bolts) and removed. We then disconnected the wire cable linkage while pulling the mechanism up and removed the bolt holding the detent roller spring assembly.
6. We removed the rest of the valvebody bolts and lifted the stock valvebody, separator plate, and gasket from the trans. At this point we were able to remove the 3-4 accumulator piston and piston pin that was located under the area where we had previously removed the 1-2 accumulator. If you’re doing this in the car, there are check balls in the valvebody that have a tendency to fall out and vanish. Just in case, TCI Automotive includes some spares since some of these will need to be used during reassembly.
7. It was then time to remove the pressure regulator from the transmission pump.
8. While pushing down on the TV boost valve sleeve we removed the retaining ring with a pair of snap ring pliers. There is some tension behind it, so beware. We were then able to remove the TV boost valve sleeve, valve, and the reverse boost sleeve and valve. The pressure regulator was left in place.
9. The top row of parts is what came out, and the lower row has the new TCI parts. There are two spring choices here. The silver one is for a firm-style shift. If you want a street/strip-style shift then add the shim to the silver spring. If you want a hard shift, then opt for the gold spring without the shim. We opted for the silver spring with the shim.
10. These are the check balls that came out of the stock valvebody. Four of the 1/4-inch silver ones are reused and, as mentioned, TCI gives you spares just in case you lose one or two. The larger copper-colored ball wasn’t reused.
11. Following the TCI instructions, we reinserted the check balls using a little grease to keep them in place.
12. The valvebody separator plate is sort of like the program that controls the “computer” that is your valvebody. The various holes and slots control and regulate the fluid movement and pressure and thus how the transmission shifts. The new one (right) looks similar to the stock plate, but when laid on top of one another there are quite a few differences.
13. Before putting the new separator plate and gasket in place, we modified the 3-4 accumulator by using the supplied self-tapping 1/4-inch x 20 Allen head plug in the casing and reinstalled the accumulator piston and spring without the black spacer. With that done and the gasket/plate assembly in place, we could install the new TCI valvebody and start bolting it down.
14. After reinstalling the auxiliary valvebody and making sure that the check valvebody was in place, we attached the rod for the manual valvebody linkage taking care not to force the valve or bend the linkage.
15. We then went ahead and reinstalled the solenoid and transmission wiring per the TCI schematic.
16. Speaking of wiring, we also took this opportunity to add a TCI lockup wiring kit (PN 376600) into the mix. This will allow hands-free, automatic activation of the torque converter clutch in Fourth gear under stable engine operation and will disengage the clutch when accelerating or downshifting. The included vacuum switch is adjustable and there’s a way to manually override and lock up the converter whenever desired. The kit included a gasket, wiring harness, vacuum switch, Fourth-gear pressure switch, splice connectors, and a mounting screw.
17. It was then time to reinstall the 1-2 accumulator assembly after installing the piston in the housing with the large orange TCI spring. For street/strip applications (like ours), we also installed the black spacer per the TCI instructions. The bolts were tightened to 8 ft-lb.
18. The throttle pressure mechanism was put back in place and the cable linkage was mated to the large lever. It’s a bit tricky as the large lever has to be held down and the small lever up while the mechanism is slipped over the roll pin on the valvebody. Once in place it was secured with the two original bolts.
19. The rest just consisted of running the new wires, installing the oil pipe (from the pump to the auxiliary valvebody), and tightening all the valvebody bolts to 8 ft-lb. The detent roller spring bolt was tightened to 10 ft-lb.
20. Using the filter seal ring included in the TCI kit, we went ahead and dropped in a new filter.
21. On the exterior of the 700-R4, we went to work on the servo. Using a large, flat-blade screwdriver we popped out the cut ring and servo cover with the blue O-ring.
22. Per the instructions, we replaced the stock servo parts with the new TCI parts and put the stack of parts back together. The red O-ring is for the secondary apply piston and not the outer servo cover, which has a blue O-ring. Mix them up and you’ll have leaks.
23. To get the most out of our Nova at the track, we ditched the stock converter and switched in a TCI Breakaway converter (PN 243107). This 10-inch converter will give us around 1,000 more rpm stall speed over stock, which should equate to quicker e.t.’s.
24. We finished off our 700-R4 overhaul with a TCI deep aluminum pan (PN 378000) that not only looks great but also has a finned design to help dissipate heat and a drain plug for easier fluid swaps. With the transmission back in the car we went through the wiring instructions and reattached the TV cable to the carburetor.
Photos by Steven Rupp
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