TH350 Transmission Build - TCI Street Stock Trans Assembly

On a recent excursion to Mississippi, CIRCLE TRACK swung by the TCI plant and got a first hand look at the process for building a TH350. Fitted to millions of street cars, turbo-hyrdomatic 350s are lightweight, easy to install, and lend themselves well to engine and transmission swaps. While in stock form, they are best suited for use behind mild small blocks and smaller engines such as V6s. However, TCI has a line of TH350s that can handle over 600 normally aspirated horsepower. That beefiness makes the TH350 the trans of choice for many street/hobby stock classes around the country. We were so impressed with TCI's operation that it gave us an idea, but you'll have to stay tuned to the next issue to find out what that idea is. So until then check out TCI's process for building a TH350.

One of the first things undertaken is the installation of the planetary.
Here is an underside view of the transmission where the valve body bolts to the case.
TCI's front pump assembly uses four Teflon sealing rings (the white and orange rings). Stock TH350s from the factory come with five cast iron sealing rings. TCI replaces the cast-iron ones with Teflon because Teflon will expand and create a better seal. In addition, TCI leaves the middle ring off which applies more pressure to the direct clutch pack and, consequently, holds better in high gear.

TCI's front pump assembly uses four Teflon sealing rings (the white and orange rings). Sto

This is the direct drum.
Here are two views of the forward drum.
When you turn it over, you can see where the clutches are in it.

The race in the intermediate sprag assembly on the direct drum is normally the weakest link in a TH350 transmission.

The race in the intermediate sprag assembly on the direct drum is normally the weakest lin
TCI solves the weak link by replacing the stock race with an aftermarket heat treated piece shown here.

TCI solves the weak link by replacing the stock race with an aftermarket heat treated piec
The rear planetary gears awaiting assembly.

The rear planetary and output shaft assembly put together.
The forward drum, direct drum, and input shaft are stacked and ready to be put into the transmission case.

The forward drum, direct drum, and input shaft are stacked and ready to be put into the tr
Now the forward drum, direct drum, and input shaft are in place.

With the input shaft and drums in place the clutches are installed. Here you can see Second gear.

With the input shaft and drums in place the clutches are installed. Here you can see Secon
Throughout the building process, the folks at TCI use a blue trans-gel assembly grease. Unlike regular assembly grease, this gel breaks down when it comes in contact with transmission fluid. It's there when you need it and gone when you don't, meaning there's no tacky grease left behind to interfere with performance.

Throughout the building process, the folks at TCI use a blue trans-gel assembly grease. Un
Checking end play is a critical step in the assembly process.

Every TCI trans is checked for leaks in the clutch pack by pressurizing the unit with transmission fluid.

Every TCI trans is checked for leaks in the clutch pack by pressurizing the unit with tran
Once a leak free transmission is confirmed, the valve body is bolted up and the pan put on.

Once a leak free transmission is confirmed, the valve body is bolted up and the pan put on
The finished TCI race ready TH350. Notice the coating on it. Called HDT, it is a heat dissipating technology that helps reduce operating temperatures. This unit is just waiting to go into a Street Stock. Hmmm...we've got an idea...

The finished TCI race ready TH350. Notice the coating on it. Called HDT, it is a heat diss