Th400

  

One of the largest questions amongst Chevy guys is TH350 vs. TH400. Which one is better. Even though they have been out of production for decades, there is still a strong demand for them. Their simplicity and durability make them attractive to people in the LS swap community. They are certainly are both great transmissions. They share the same bolt housing patterns, and often came behind the same engine types. Whereas the TH350 would be found behind a lower performance small-block 350 Chevelle, the TH400 would be the transmission that came with the 454 SS. The TH400 also found itself in many heavy duty trucks and vans.

TH400 Performance Automatic Transmissions and Parts from PATC. PATC GM Performance Transmissions and Parts, TH400 and others. PATC builds TH400 performance transmissions in many levels. PATC is on the cutting edge of performance rear wheel drive American transmission development. The TH400 9 inch tail housing with the 27 spline output shaft has the same mount position as the 4 inch tail housing. With some modification to the 2 mount bolt holes on the crossmember this extension housing can eliminate crossmember modifications when replacing a TH400 with a 4 inch tail, 9 inch tail with a 27 spline output shaft or 200-4R. Street/Strip and Drag Racing TH400’s Stage 1 TH400 – 450 HP/TQ capable. Our Stage 1 TH400 is a heavy duty rebuild with valve body and hydraulic improvements, rollerized rear thrust, heavy duty intermediate snap ring, and OEM pan. 450 HP/TQ capable but proven at much higher HP levels. Shop TH400 Torque Converters and get Free Shipping on orders over $99 at Speedway Motors, the Racing and Rodding Specialists. TH400 Torque Converters in-stock with same-day shipping. Turbo 400 on sale with Free Shipping, Now offering TH400, TH-400, Monster 400 Transmission, heavy duty Th400 and heavy duty Turbo 400 with new lower prices.

TH350TransmissionTH400
First- 2.52

The knife movie. Second- 1.52

Third- 1.00

Gearing

First- 2.48

Second- 1.48

Third- 1.00

32

Input Shaft Splines

32

27

Output Shaft Splines

32

21 5/8”

Length from Bellhousing to Tailshaft

25”

The TH350 is certainly smaller than the TH400 and can usually fit into nearly any rear wheel drive Chevrolet passenger car with no problem. Tunnel modification can come into play on some of the smaller cars. The TH350 uses a mechanical kick down switch, whereas the TH400 uses an electric one. The electric kick down is much easier to set up, espescially if you are doing an LS Swap,

They do both have an aluminum case, and three forward gears. Although the gear ratios are nominally different. Neither transmission has any sort of computer control to it, nor did they use locking converters.

A lot of people claim that he TH350 has less drivetrain loss than the TH400, which means that all things being equal, the TH350 is going to get more power to the rear wheels from an engine with equal power. This is due to more rotating weight existing in the larger TH400 case. Here is a writeup on ET loss from TH350 to TH400.

Th400 Transbrake

They also don’t weight the same amount. The Turbo 350 weights 150pounds while a Turbo 400 weighs almost 170.

If you are going to buy a stock transmission and know it’ll fit in your vehicle, without a doubt the TH400 is the way to go. It’s super durable and will provide a long life of useful service with no modification from stock, even in higher horsepower situations.

If you are buying an aftermarket transmission from someone like TCI or Monster transmission, I’d say go with the TH350. These folks have had decades to get all the flaws and weakness out of it. You’ll have less mass in the drivetrain and a lighter transmission.

Th400 transmission diagram

Th400 Diagram

Thank you for reading!

Related: TH350 vs 4L60E: Comparing the Differences, Th350 vs 700R4 Differences