S197 Owners rejoice: D&D Performance has bundled together a bolt-in, six-speed package centered around its proven Viper T56 gearbox. The $4,995 kit has everything needed for the swap, including an upgraded clutch disc and a one-piece aluminum driveshaft. Well, OK, you still have to supply a couple buddies with strong backs.
Quick, if the new Mustang GT has one weakness, where would it be? Hmm, let's see, it has 300 horses right from the factory; rides, handles, and launches like no Mustang before; has world-class looks outside and in; and heck, it even has 31-spline axles and 3.55 gears. Ah, but its standard tranny is just a five-speed, and there's no six-speed on the option list. Well, friends, take heart, because D&D Performance now has you covered with a '05-'06-specific version of its legendary Viper T56 gearbox.
Now don't go taking this as undue criticism of the GT's factory Tremec 3650, which is a robust box that can handily shrug off OEM power levels. But let's have a show of hands from all you readers planning on leaving your S197 at the factory power level. Thought so. Strength aside, perhaps the S197's least satisfying tranny aspect, especially for the quarter-mile crowd, is a factory setup that has the shifter mechanism hanging back behind the transmission, connected to both the gearbox itself and the car's unibody. Naturally, the transmission, firmly attached to the engine, squirms around in relation to the body, so the shifter's link arm to the 3650 has to allow for this motion with a very soft rubber mounting bushing. Not surprisingly, this lends a correspondingly rubbery feel to the shifter in everyday driving; worse yet, it also makes a 2-3 speed-shift rather challening under the torque load of wide-open throttle.
Luckily, D&D's Viper T56 swap simultane-ously addresses both shortcomings. As its name implies, this bull-strong six-speed was originally designed for the monumental torque output of the Dodge Viper's 8.3-liter (English translation: 506ci) V-10. D&D's Don Walsh Sr. pegs its torque-handling capability at around the 650 lb-ft mark. It also offers nice, tight ratio spacing (see sidebar), starting with a 2.66:1 First gear, all the way up to a highway-friendly 0.50:1 Sixth. That deep Overdrive turns the GT's 3.55 axle ratio into a fuel-stingy 1.78:1 (as compared to the 2.41:1 overall ratio generated by the 3650's 0.68 Fifth gear.) While fuel economy won't be the primary reason you'll want a Viper T56, these days it certainly doesn't hurt.
As a real bonus, the D&D Viper T56 also does away with the half-tranny, half-body shifter mounting scheme, replacing it with a much more conventional-and precise-setup borrowed from the current Pontiac GTO parts bin, of all places. Another return to convention is the kit's included one-piece aluminum driveshaft, replacing the S197's stock, heavy, two-piece, articulating shaft, and necessary not just because of tranny-to-axle length differential, but also because the T56 reverts to a familiar slip-yoke output instead of the S197's factory companion-flange arrangement. If this all sounds a little muddy, our accompanying photos and captions should help clear things up.
Part of the Viper T56's Herculean strength comes from its 26-spline input shaft (the 3650, in Ford tradition, has a 10-spline input), so the D&D package also brings along a new D&D/McLeod Super Heavy Duty clutch disc for use with the stock pressure plate. Speaking of clutches, the S197's is hydraulically disengaged, instead of the cable release used on older Stangs. D&D's S197 version of Viper T56 is specifically engineered to accept the stock hydraulic throwout bearing.
In other words, this is a comprehensive, basically plug-and-play kit that D&D Performance offers, and installation is straightforward, as Don Walsh Jr. and crew at Walsh Motorsports demonstrate.
The backbone of the package...
The backbone of the package is the hand-assembled D&D Viper T56 gearbox that is capable of handling way more torque than the factory 3650 five-speed. Internally, the Viper T56 is bolstered by its specific gearset (see sidebar), which provides a particularly hardy input-gear-to-countershaft-gear ratio. D&D also engineered a specific bellhousing to accommodate the S197's hydraulic clutch line. A shifter, too, is part of the kit.
Because of the S197's more...
Because of the S197's more easily reached rearward shifter location in comparison to Fox-derivative Mustangs, D&D's S197 Viper T56 employs a Chevy F-body tailhousing casting fitted with an '05 Pontiac GTO shifter base, as seen in the foreground. Compare this aft shifter location to the '00 Cobra R-style T56 in the background.
Here's the factory S197 shifter...
Here's the factory S197 shifter arrangement, hanging way off the back of the 3650 and bolted to it via a very soft bushing. The linkage mechanism is, to say the least, remote. Also note the two holes at the back of the shifter plate, by which it gets bolted to the unibody's tranny tunnel. It's no wonder this setup binds during aggressive shifting. Thankfully, D&D's S197 Viper T56 does away with this dual-mount setup altogether.
The Viper's input is via a...
The Viper's input is via a beefy 26-spline shaft (the 3650 uses 10-spline input) necessitating the kit's correspondingly splined clutch disc. D&D also had to engineer a provision (the billet ring around the input) to mount the S197's hydraulic throwout bearing. That hydraulic operation also necessitated the small cutout visible on the bellhousing, to allow for the fluid supply line.
The kit's clutch disc is D&D's...
The kit's clutch disc is D&D's Super Heavy Duty unit (a McLeod piece) having the required 26-spline hub. As can be seen, a shim plate is also included to account for the increased disc thickness (0.310 inches versus a stock 0.270.)