TH400 Valve Body, used and ready to install. Fits the TH400. Ships fast from the USA.
If your GM truck, motorhome or full-size car with the TH400 will not hold 1st gear under load, slips or bangs between gears, or has a shift feel that has gotten worse over time, the valve body is the usual place that traces back to on this transmission. This is a used, tested TH400 valve body, so you install a known-good hydraulic section instead of guessing which bore or spool valve inside the original has worn out of spec.
The TH400 is a fully hydraulic 3-speed with no onboard computer - a vacuum modulator and a governor feed the valve body mechanical signals for engine load and road speed, and the valve body's own bores and spool valves turn those signals into line pressure and shift timing. Because there is no electronic fail-safe, wear inside the valve body shows up directly as a shift or pressure complaint rather than a stored code, and a problem that looks like a clutch failure can just as easily be the valve body failing to apply that clutch correctly.
Before assuming the valve body, check for a known TH400-specific failure at the direct drum: the low roller clutch that locks the reaction carrier to the center support in 1st gear can pop its rollers out of the race under high torque, crushing the accordion springs behind it and taking out the direct drum along with it - a mechanical failure that mimics a valve body problem but requires drum and clutch parts, not just a new valve body. If the reverse servo has never been adjusted, a drag or a late apply there can also look like a pressure problem upstream. Our TH400 common problems and fixes guide covers the low roller clutch failure in detail, and the TH400 filter and pan service guide is the right place to start before you pull the pan to swap this part.
The TH400 covers an unusually wide range of applications from 1964 through 1990 - GM half-ton and heavier trucks, motorhome chassis, full-size performance and luxury cars, and the Jaguar and Rolls-Royce models GM supplied this transmission to during that span. With a run that long, casting marks, governor type and modulator thread all changed more than once, so confirm those details against the listing photos before ordering, or send your application so we can match the correct version. The full TH400 parts collection covers everything else we stock for this transmission.
While the pan is down, check the low/reverse servo piston travel - the factory spec is 0.125 in, and either too little travel (band drag with no reverse) or too much (the piston bottoming before the band fully applies) will undo the benefit of a fresh valve body. Torque the valve body bolts in sequence to spec and refill with Dexron ATF to the correct capacity for your case. If the unit is behind added horsepower, the stock input shaft is a known weak point under load - pair this valve body with a TH400 overhaul kit and a stronger TH400 pump rather than bolting new valving behind parts that are already marginal.
| Fits | TH400 |
| Part type | Valve Body |
| Condition | Used |
| Brand | OEM |
| Ships | From the USA |
| Warranty | 1-year |
Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
The valve body itself can fail to route pressure to apply first gear correctly even when the clutch packs are good, which is why a no-first complaint does not always mean a clutch failure.
The low roller clutch at the direct drum can pop its rollers out of the race under high torque in 1st gear and crush the accordion springs behind it, producing a shift complaint that looks hydraulic but is actually a worn direct drum.
Factory low/reverse servo piston travel is 0.125 in. Too little causes band drag with no reverse; too much lets the piston bottom out before the band fully applies.
The TH400 was produced from 1964 to 1990 across trucks, motorhomes, and full-size cars with multiple casting and governor revisions, so match your casting marks and modulator thread against the photos or send your application to confirm.
No - the TH400 is fully hydraulic with no onboard computer, so there is nothing to relearn. Road test after the fill and recheck if shift feel is still off.
Probably not by itself. The stock input shaft is a known weak point under added power, so pair this valve body with a stronger pump and, if you are pushing serious torque, an upgraded input shaft rather than relying on the valve body alone.
