The TH400 (or Turbo 400) transmission is one of the most versatile and widely used performance transmissions in the automotive industry. From street rods and offroad desert trucks to all-out drag racing, the TH400 transmission has proven itself to be very adaptable and capable of handling massive power — not only in General Motors applications, but also adapted behind Ford, Chrysler and import engines. For builders looking to maximize performance and reliability like never before, Sonnax offers an expanding line of game-changing TH400 upgrades proven to deliver results you can trust at any power level.
The TH400 (or Turbo 400) transmission is one of the most versatile and widely used performance transmissions in the automotive industry. From street rods and offroad desert trucks to all-out drag racing, the TH400 transmission has proven itself to be very adaptable and capable of handling massive power — not only in General Motors applications, but also adapted behind Ford, Chrysler and import engines. For builders looking to maximize performance and reliability like never before, Sonnax offers an expanding line of game-changing TH400 upgrades proven to deliver results you can trust at any power level.
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Wouldn’t be able to put together transmissions without your upgrades, great parts and great quality!
D. Balbuena
TH400 Build Guide
This chart breaks down the five types of Sonnax TH400 transmission parts available at different performance levels. Combine these with other Sonnax TH400 upgrades for a top-notch rebuild.
| Area of Enhancement | Individual Components | All-In-One Upgrade | |
| Input Shaft | 1" Heavy Duty (1 Journal) 1" Heavy Duty (2 Journal) | 1-1/8" Extreme Duty 1-3/16" Extreme Duty | — |
| Forward Drum | Heavy Duty Ideal for Any Power Level | Smart-Tech Drum Module Ideal for Any Power Level | |
| Direct Drum | — | — | |
| Clutch Hub | Heavy Duty | Extreme Duty | |
| Main Shaft | Heavy Duty | Extreme Duty | — |
| Input Shaft |
| Individual Components |
| 1" Heavy Duty (1 Journal) 1" Heavy Duty (2 Journal) |
| 1-1/8" Extreme Duty 1-3/16" Extreme Duty |
| All-In-One Upgrade |
| — |
| Forward Drum |
| Individual Components |
| Heavy Duty Ideal for Any Power Level |
| All-In-One Upgrade |
| Smart-Tech Drum Module Ideal for Any Power Level |
| Direct Drum |
| Individual Components |
| — |
| — |
| All-In-One Upgrade |
| Smart-Tech Drum Module Ideal for Any Power Level |
| Clutch Hub |
| Individual Components |
| Heavy Duty |
| Extreme Duty |
| All-In-One Upgrade |
| Smart-Tech Drum Module Ideal for Any Power Level |
| Main Shaft |
| Individual Components |
| Heavy Duty |
| Extreme Duty |
| All-In-One Upgrade |
| — |
Our Sonnax-equipped, in-house built TH400 survived hot lapping 3 - 4 passes every day for 5 days and survived on the 1,200-mile drive flawlessly. Tough Sonnax parts for Drag Week’s most competitive and toughest class.
Steve & Dustin Trance • Hot Rod Drag Week Class Champions
- Increase wheel horsepower, improve acceleration & reduce shock on shifts while ramping up durability & safety
- A great value: all-in-one kit upgrades forward & direct drums plus everything else from intermediate sprag to back of the pump
- Unique design improves efficiency without reducing capacity
- Easy to assemble & install
When racing a TH400, it’s critical to upgrade the forward and direct drums. The key is not only stronger, more durable parts, but improving efficiency for better performance, consistency and safety.
Grab a radical edge over the competition with the Sonnax Smart-Tech drum module. It’s the first and only TH400 upgrade to optimize drum function with a unique configuration of both lighter and stronger components. The result: a big boost in transmission efficiency for more power to the ground, traction/stability on the shifts and the best protection you can get against catastrophic drum failure.
Get Your Next Number | Get Smart-Tech
The cutting-edge Smart-Tech drum module is takingdrag racers to the winner’s circle while settingrecord after record for E.T., MPH and consistency.
FACTORY STOCK
BRACKET RACERS
DRAG-N-DRIVE
SMALL & BIG TIRE
1/8 & 1/4 MILE
STOCK, SUPER STOCK,
COMP ELIMINATOR
PRO MOD
“All the claims are true, no hype. If you are the type of racer that is always seeking an edge, this is worth it in many different scenarios.”
’21, ’22 & ’23 Drag Week Class Winners
Dustin & Steve Trance
Get Your Next Number
Get Smart-Tech®
The cutting-edge Smart-Tech drum module is takingdrag racers to the winner’s circle while settingrecord after record for E.T., MPH and consistency.
FACTORY STOCK
BRACKET RACERS
DRAG-N-DRIVE
SMALL & BIG TIRE
1/8 & 1/4 MILE
STOCK, SUPER STOCK,
COMP ELIMINATOR
PRO MOD
“All the claims are true, no hype. If you are the type of racer that is always seeking an edge, this is worth it in many different scenarios.”
’21, ’22 & ’23 Drag Week Class Winners
Dustin & Steve Trance
How It Works
Just like you might run lighter wheels, a lighter driveshaft or rotating assembly in your engine to reduce rotational mass and improve performance, you can achieve a similar effect inside your transmission with the Smart-Tech drum module.
The OE drum design limits performance.
In a standard TH400, when the unit shifts from 1st to 2nd to 3rd, the direct drum and internal components are spinning up backwards, completely stopping and then re-accelerating to input RPM. At racing RPMs this takes a huge amount of energy and puts a lot of strain on the transmission, which is why parts fail when they hit their limit. The traditional method of installing lighter components to improve performance won’t overcome this basic inefficiency of the TH400.
The Smart-Tech drum module gives you a better option.
Sonnax re-engineered the entire forward/direct drum system so only a few parts counter-rotate instead of the entire direct drum: the inner sprag shaft, aluminum clutch hub and friction plates. Weighing 3.3 lbs less than an aluminum drum, with weight concentrated at the center, the Smart-Tech drum module's direct clutch components take 53% less energy to start/stop/re-start than an aftermarket aluminum drum. This is a HUGE advantage no matter vehicle power level or what type of racing you’re looking to do. Plus, direct drums that explode due to overspeeding are simply no longer a threat thanks to the module’s unique design.
Learn More
Watch this video to learn more about the Smart-Tech drum module, Part No. 34555-01K, or see product specs and instructions here.
Plus, check out these frequently asked questions.
Sonnax high performance products meet the toughest challenges faced by hard-working, daily-use drivetrains as well as racing units going all-out on the street or track.
