TH400 valve body for 1965-1990, Sonnax-updated and ready to install. Ships fast from the USA.
A stock TH400 shifts on governor and throttle-valve pressure and has no way to hold the car against the converter at the line - this kit replaces the entire valve body with a billet aluminum, full-manual unit that stages on a button and lets you pick every gear yourself, built for drag applications on the 1965-1990 TH400 that need to survive hundreds of hard launches, not just one.
Full manual means the governor and throttle-valve logic that a street TH400 relies on are gone - every upshift and downshift happens because you moved the lever, on a P-R-N-1-2-3 pattern, not because the transmission decided conditions were right. Built into the same unit is a trans-brake solenoid that holds first and reverse clutches together at once, locking the output shaft so you can bring the engine up against the converter with the brake off and the car staying still, then drop the button for the launch. Machining the body from billet aluminum instead of using a cast core matters here because a trans-brake unit sees the same bores load and unload hundreds of times a season under full line pressure - billet holds that dimensionally where a tired cast bore starts to bleed pressure and soften the stage.
We also stock a kit that keeps the TH400's stock forward shift pattern and only adds a transbrake circuit to an otherwise automatic valve body, and a separate reverse-pattern transbrake kit - if you want full manual control plus staging in one billet unit, this is the one built for that combination.
This covers the TH400 as used in 1965-1990 GM trucks, motorhomes, high-performance cars, and the Jaguar and Rolls-Royce applications that also ran this transmission, but a full-manual trans-brake valve body is a dedicated race part, not a bolt-in behind a stock column shifter. Match your case casting and confirm your shifter, linkage, and wiring can support full manual shifting and a staging button before ordering. The TH400 parts collection has the rest of what we carry, including the reverse-pattern transbrake kit and the stock-pattern transbrake kit if this full-manual version is more than your build needs.
Wire the trans-brake solenoid to its own dedicated button, isolated from the reverse-light and neutral-safety circuits, and verify line pressure at both the staging circuit and normal drive before making a pass - our TH400 valve body testing guide covers where to read those numbers. Change the fluid and filter with a fresh filter and pan gasket set so debris from the old valve body does not circulate into this one, refill with Dexron ATF, and give the transmission a dedicated cooler sized for the heat repeated staging builds, since that load is well beyond what the stock cooling path was designed around. A unit that has not been rebuilt recently should get a fresh overhaul kit before this valve body goes in, since full line pressure under a trans-brake punishes worn clutches fast.
| Transmission | TH400 |
| Year Range | 1965-1990 |
| Condition | Remanufactured / updated |
| Shipping | Ships from the USA |
Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
This replaces the governor and throttle-valve shift logic entirely. Every gear change happens because you move the lever on a P-R-N-1-2-3 pattern, and a built-in solenoid holds first and reverse together for staging - a stock or mildly shift-kitted valve body still shifts on its own.
A trans-brake unit cycles the same bores under full line pressure hundreds of times a season. Billet aluminum holds those bores dimensionally stable longer than a cast core, which keeps the stage and the launch consistent as the season goes on.
No. Full manual shifting and a dedicated trans-brake button need an aftermarket shifter and separate wiring, not the stock column or console shifter and its reverse-light and neutral-safety circuits.
We also carry a kit that keeps the stock automatic shift pattern and only adds a transbrake circuit, and a separate reverse-pattern transbrake kit without full manual control. This billet kit combines full manual shifting with the integrated trans-brake in one unit.
Line pressure at both the trans-brake circuit and normal drive pressure, cooler capacity for the heat repeated staging generates, and the condition of the clutches behind the valve body - a trans-brake loads them harder than normal driving.
Dexron ATF, with the fluid and filter changed at install so old debris does not circulate into the new valve body, and a fresh overhaul kit if the transmission behind it has not been rebuilt recently.
