TH350 Reaction Shell, used and ready to install. Fits the TH350. Ships fast from the USA.
Looking for a TH350 reaction shell because your Turbo 350 lost second and third, makes a grinding or clunking noise under load, or showed a cracked shell or chewed-up sun gear splines on teardown? This is a refurbished TH350 sun gear drive shell, the part many catalogs call the reaction shell, supplied with its sun gear. It is the lightened, perforated style with large windows cut around the barrel, a popular choice for performance builds because it takes rotating weight out of the geartrain. It is a used, cleaned and inspected part, not new.
The TH350 runs two planetary gearsets, front and rear, that share one long sun gear. The sun gear drive shell is the bell-shaped piece that wraps around the output carrier and connects that sun gear to the direct clutch housing. GM's assembly procedure has the tangs on the direct clutch housing drop into slots on the shell, so whatever the direct clutch housing does, the sun gear does too. In second gear the intermediate clutch and intermediate roller clutch hold the direct housing, which holds the shell and stops the sun gear. In third the direct clutch locks the housing to the input, so the sun gear turns with the engine and the gearset locks into direct drive. In Reverse the direct clutch drives the sun gear while the low and reverse clutch holds the reaction carrier. That makes the shell a load path in second, third and Reverse, and a weak point when it cracks or its tangs wear.
A slipping intermediate clutch, a worn intermediate roller clutch or a burned direct clutch can produce the same no-second or no-third complaint, so start with a pressure test and a road test through every range. GM's diagnosis charts separate those clutch faults from mechanical ones, and our TH350 common problems and fixes guide lays out how to tell a no-second from a no-Reverse failure. If pressure is good and the unit still loses drive, or you hear a mechanical clunk, drop the pan. Metal debris, rather than just friction material, is the sign to pull the unit and inspect the shell, the sun gear and the planetary carriers. Once it is apart, look for cracks at the base of each slot and twist the sun gear in the shell to feel for spline wear.
The listing fits the GM TH350. Lightweight aftermarket and refurbished shells are sold to drop into the stock TH350 geartrain, but check that the sun gear length, spline count and the shell's slot pattern match the original you removed, especially if your unit has been modified or came from a TH350C. If you are not sure what you have, send us the year, the vehicle and the VIN or transmission ID and a photo of your old shell, and we will confirm before it ships. You can see every part we stock for this transmission on our TH350 parts page.
Because a shell failure usually sends debris through the unit, most rebuilders replace the soft parts at the same time with an ATP SMS-9 master repair kit. Inspect the direct clutch housing tangs and the carriers too; we also stock the TH350 direct clutch drum and a TH350 rear planetary if either is damaged.
| Fits | TH350 |
| Part type | Reaction Shell |
| 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.
Yes. GM calls it the sun gear drive shell. Many parts catalogs call it the reaction shell or input shell. It connects the direct clutch housing to the sun gear shared by both gearsets.
Yes. The listing is a refurbished sun shell supplied with the sun gear. It is a used part, cleaned and inspected, not new.
The windows cut into the barrel reduce rotating weight in the geartrain, which is why lightened shells are popular in performance builds. Inspect any shell for cracks at the slots before installing it.
Loss of second, third or Reverse with good line pressure, a mechanical clunk or grind, and steel debris in the pan. Clutch failures can mimic it, so pressure-test first.
New sun gear retaining rings, the shell thrust washers, worn sun gear bushings and, because the failure contaminates the unit, a full master repair kit and a new filter.
