TH400 Planetary 1973, used and ready to install. Fits the TH400. Ships fast from the USA.
A Turbo 400 that whines louder as road speed climbs, has lost Low or Reverse, or left chunks of bronze and steel in the pan has usually hurt its gear train. This listing is a used TH400 planetary gear unit pulled from a running, drivable 1973 Cadillac DeVille that was parted out. It is the hard-parts core of the gear train: the output carrier, the reaction carrier, the sun gear, the sun gear shaft, and the rear internal gear with its mainshaft. It is clean, early-1970s GM hardware, the right choice when your own carriers have chewed pinions or a broken shaft and you would rather install matched original parts than mix aftermarket pieces.
The TH400 gets its three forward speeds and Reverse from a compound planetary gearset: two planet carriers sharing one long sun gear. The rear internal gear rides on the end of the mainshaft, which is driven by the forward clutch. The reaction carrier is the part that gets held to make Low and Reverse; the rear band wraps around its outside, and the low roller clutch runs inside it and locks it to the center support in First. The output carrier carries the parking pawl lugs and splines to the output shaft. The sun gear shaft links the sun gear to the direct clutch drum, so when the direct and forward clutches both apply the whole set turns as one for Third.
Pull the pan and look at the debris. Fine friction material points to clutches; bronze and steel chips point to bushings, thrust washers and pinions. Once the unit is apart, GM's inspection steps are the test: check each carrier's pinions for damage, rough bearings or tilt, measure pinion end play (GM lists .009-.024 inch), inspect the reaction carrier band surface and roller race for burning or scoring, and check the mainshaft and sun gear shaft for cracks and worn bushing journals. The TH400 common problems and fixes guide explains the low roller clutch and drum failures that often take a reaction carrier with them, and the TH400 filter and pan service guide shows how to read what is in the pan.
This gear unit came out of a 1973 Cadillac DeVille TH400. The planetary parts were used across many GM applications, but shafts and carriers did change over the years, and GM itself notes two reaction carrier styles (with and without a spacer ring under the roller cam ramps) that interchange. Before you order, compare your old mainshaft length and splines, the sun gear shaft and the pinion count on each carrier against the photos, or send your year, make, model and engine and we will check it. Other years are on the TH400 parts page, including a TH400 planetary listed for 1964-98.
Rebuilding around this gear train? The TH400 overhaul kit for 1965-1987 supplies the seals and gaskets, and the TH400 clutch drum is worth checking if the drums show heat damage.
| Fits | TH400 1973 |
| Part type | Planetary |
| 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 output carrier, reaction carrier, sun gear, sun gear shaft, and rear internal gear with its mainshaft. Thrust washers, bearings and races, the low roller clutch and the front internal gear ring are not included.
Used. It came out of a running, drivable 1973 Cadillac DeVille TH400 that was parted out. Inspect pinion end play and the bushing journals on arrival like you would any used hard part.
The core planetary parts were shared across many GM TH400 units, but shafts changed over the years. Compare mainshaft length and splines, the sun gear shaft and the carrier pinion count with your parts, or send your year, model and engine and we will check it.
Usually worn pinion needle bearings, worn thrust washers or a lack of lube flow from worn bushings. GM's check is to look for rough pinions and excessive tilt and to measure pinion end play, which should be .009-.024 inch.
All thrust washers and bearings, the low roller clutch if it is worn, the sun gear shaft bushings if scored, plus a seal and gasket overhaul kit. Use Dexron ATF and set rear unit end play to .007-.019 inch.
