Spare Parts You Should Carry With You For Your Race TH400 Transmission

Posted by on Wednesday, May 21st, 2014

The TH400 is a three speed automatic transmission designed and built by General Motors.  It is the heaviest duty automatic transmission GM build during the 1960’s through the 1980’s. It was eventually succeeded by the four speed automatic overdrive 4L80E transmission.  Originally, the TH400 could be found in heavy duty pickup trucks, large sedans and high-performance vehicles. It was used in the C20 and C30 pickup trucks, the big block equipped Impalas, the Chevy Corvette, the Chevy Camaro, the Pontiac Trans Am, the Cadillac DeVille, the Chevy El Camino and the Chevy Suburban.


Due to its internal high strength components, the TH400 became a popular transmission in drag race cars, hot rods and was a popular swap for just about any high performance application. Although the TH400 is a very strong transmission, it was not without its weak points. Just like any other mechanical device, if you push it hard enough something will break. For this reason we have come up with a list of spare parts you should carry with you if you plan to race a TH400 in your high performance application.

Spare clutches – It’s always a good idea to keep a couple spare clutch kits. I recommend that you go with the Raybesto high performance clutches. There are also a number of exotic material clutches available for all out racing applications, such as those made of Carbon Fiber from TCI Automotive.

Spare bands – Just like the clutches mentioned above, I would stick to the Raybestos high performance bands, or something better. Different materials can be used for different track and weather conditions.

Input shaft – Input shafts take a lot of abuse when put behind a race motor, especially one that is running a nitrous systems or supercharger. Throw in a car with a high performance suspension and big fat slicks, and the abuse gets worse. The best input shafts are made from a material called 300M. It can handle a lot of abuse and keep on going. Keep in mind that when an input shaft fails, you’re probably looking a damage to the front pump, bushing or torque converter.

Planetary gear set – There is a couple reasons to carry a spare planetary gear set. The first it to replace a unit that has broken, or a component of the planetary gear set such as an axle. The second reason is to have at your disposal a number of gear sets with different gear ratios. As weather conditions, altitude, track conditions or track length change, it might be to your benefit to swap out to a different gear set ratio. After all, races are loss and won by just a fraction of a second, and a different gear ratio can make all the difference.

Gaskets- Of course you’re going to want to keep a number of gasket sets on hand. Just about anything you do to change the internals of a transmission will require a gasket change. Don’t get cheap and try to re-use an old gasket. Leaking transmission fluid can get on your tires, leading to a crash, or at the very least, you will be disqualified from racing.

Fluid – Just like the gaskets mentioned above, any time you make an internal change to the transmission, you will need to replace the fluid. I highly recommend going with a synthetic transmission fluid. Use of a synthetic fluid will reduce wear, and more importantly, will reduce internal friction, which may end up benefiting your vehicles in the form of slightly reduced quarter mile times.

Torque converter – There are two good reason to carry a few spare torque converter. First, you always want to have a spare in the event that you break a torque converter. Second, having a number of converter with different stall speed will allow you to adjust for weather and track conditions accordingly. The latest trend is to have a bolt together torque converter. This will allow you to swap out the stator, change the fin angle or make internal repairs, requiring you to only carry one spare instead of multiple units.

My best advise it to start with a transmission that has been re-manufactured instead of one that was simply rebuilt. A re-manufactured transmission will include major internal modifications and upgrades designed to make it both stronger and more durable. A rebuilt transmission will not include this feature. A re-manufactured transmission also comes with a much better warranty; three years compared to an average 90 days for a rebuilt transmission. And in the rare event that you need to contact the company that re-manufactures transmissions, they are just a quick phone call or email away!

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