In the auto trans world, few transmissions can handle the type of power the TH400 can when it's upgraded from stock. Unlike the Powerglide, which is mainly a drag racing trans, the TH400 is a viable choice for both street cars and hard-core strip racers.
We had a few options when it came to choosing a transmission for our '63 Nova hardtop project. For example, we thought of fitting a manual trans in the tunnel, but we decided it would be more effective at the dragstrip with an automatic. A quick call to TCI Automotive in Ashland, Mississippi, and we had one of their competition TH400's on the way. TCI offers a quite a few choices for those looking for GM's beefy three-speeds: the Street Rodder, which can handle up to 525 hp is intended for milder street cars; the Street Fighter, a TH400 intended for non-supercharged cars up to 750 hp; the Super Street Fighter, which can handle 750-1,025 hp naturally aspirated; the Circle Track version, which is a lightweight full-manual intended for that style of racing; the Heavy Duty/Towing version; and the fifth option-the one we ordered for our car-the Drag Race model.
Because we plan on competing in the NMCA West's True Street class, where competitors drive a 30-mile cruise before making three back-to-back quarter-mile passes, we needed something that could not only handle the horsepower, but could also be streetable. A Powerglide could certainly handle it, but would limit the driveability. The TH350 is lighter and would be great for the street, but it wouldn't be able to take what we plan on putting in front of it, so the TH400 was the way to go. The Drag Race transmission from TCI is upgraded with the hard parts needed to make it stand up behind the most grueling engines, but what really separates it from the others is the transbrake.
By using an electric solenoid that attaches to the transmission valvebody, the transbrake essentially reroutes hydraulic pressures in your trans to hold both the reverse and forward clutches when you hold down the button simultaneously. This keeps the car from moving, and it's at this point you put your foot to the floor and when it's time to launch, let go of the button and hold on. The benefit of this is to get the most stall speed out of your torque converter, and it also adds consistency compared to launching off of a foot brake.
In the following pages we show you some of the internal components that go into TCI's TH400, from the clutches to the transbrake valvebody, that will make launching a 2,800-pound nitrous'd street car a total blast. The next time you see this piece it will be sitting underneath our '63 Nova ready to rock.
|TH400 Gear Ratios|
For several years, TCI has been buying up all the popular performance automatics in bulk from various sources, so don’t expect them to run out anytime soon. Each case is cleaned and inspected for cracks before the assembly process begins. The case is covered with a heat-dissipating coating as well.
Although TCI uses the stock pump housing to lubricate their transmissions, they upgrade the setup with thicker gears, which help keep the internals cooler from a higher volume of fluid flowing in the trans at all times. Having a deeper transmission pan also helps keep it cooler internally due to the increase in volume.
Simply changing out the stock clutches and bands to some “grippier” components in the TH400 can change its power-holding capabilities tremendously. Alto Red Eagle clutches sandwiched between Kolene-coated steels is what TCI uses in most of their Competition and Super Street Fighter transmissions. The Kolene is a coating that helps dissipate heat, which is the number-one cause of death in the transmission world.
Speaking of heat, we plan on using a pair of these transmission coolers to keep our TH400 cool during hot cruises on the freeway and dragstrip blasts at the track.
We’ll be running TCI’s Max Shift fluid in our TH400, which is a top-tier blend, made for the rigors of high performance and racing. It reduces internal friction and heat, while proving more grip for the clutches. Antifoam and other additives are also used in Max Shift to increase shift quality and promote longer trans life.
The TH400 intermediate drum gets stuffed with three Alto clutches, while the forward holds five. The reverse band, which grabs the drum when the transbrake is engaged, is also upgraded to Alto performance frictions.
The transbrake is a simple electric solenoid that, when engaged, positions a modulator in the valvebody that routes fluid to the forward drum and reverse band. Basically, this little guy allows you to get the most stall speed from your converter, but more importantly, it lets you launch your car with your foot matted to the floor.
Being the brains of the transmission, the valvebody gets inspected and installed with a shift improving kit at TCI before it’s tested on a special valvebody dyno at their headquarters in Ashland, Mississippi.
Because we’re running a full-manual valvebody with a ’brake, the stock governor (the cap with five fasteners in the lower right) is not used. In a stock application the governor controls the shift timing, but since we have to shift it with our arm it’s not needed.
A 34-element sprag is used on the intermediate drum, which further increases the TH400 power-handling abilities.
We also opted to run a stall converter from TCI, which we had upgraded to have anti-balloon plates so we don’t blow up the converter when we do end up making big power. This also has the HDT coating, and we ordered it up with about 3,500 rpm of stall, but we do realize the actual leave rpm will depend on how much torque we make. If we make some monster torque it could go even higher than that. Other upgrades include Torrington needle bearings, increased thrust capacity, and furnace brazing process that keeps it together.
Also, look for an install where we bolt up one of TCI’s Outlaw Shifters with an in-handle transbrake button.