4T40E Reaction Shell, used and ready to install. Fits the 4T40E. Ships fast from the USA.
When a 4T40E comes apart and the reaction sun shell has stripped teeth, a cracked web or a hub that has been spinning on its bushing, a rebuild kit alone will not put the car back on the road. This listing is a used GM 4T40E reaction shell, pulled as a good hard part, for the four-speed front-drive transaxle in the Chevrolet Cavalier, Malibu, Cobalt and HHR, Pontiac Sunfire and G5, Oldsmobile Alero and Saturn Ion. It is the part a rebuilder reaches for after a teardown turns up a damaged shell and the price of a new one is not worth it on a high-mileage car.
The 4T40E stacks two simple planetary sets behind its drive chain. The JP Automatic Transmissions parts catalog identifies the front set as the reaction planet, which runs on a 42-tooth sun gear that is part of the reaction sun shell, and the rear set as the input planet with a 46-tooth input sun gear. The shell is the bell-shaped piece that wraps around the geartrain and carries that sun gear on its center hub, so whatever holds or drives the shell controls the front sun gear. Needle thrust bearings sit on both faces of it, including one between the reaction carrier shaft and the sun shell, which is why end play and bearing condition matter so much here.
Rebuilders use similar names for two different pieces in this unit. The catalog also lists a reaction carrier shell, which is bushed front and rear and sits behind the input sun gear shaft. Compare the product photo with the part you removed: this one is a windowed shell with the sun gear hub in the center.
A shell problem is a teardown diagnosis, not a scan-tool one. Before the unit comes apart, rule out pressure and electrical faults so you are not replacing hard parts for a valve body issue; our slipping diagnosis guide lays out the order. Once it is apart, inspect the sun gear teeth, the splines and the hub bushing surface, and check every thrust bearing in the stack. Our thrust washer and end play guide explains what excessive end play does to these parts.
The JP catalog lists the reaction sun shell with the 42-tooth sun gear as one design for 1995-up 4T40E transaxles. GM used the 4T40E in front-drive cars from 1995 into the late 2000s, including the Cavalier, Sunfire, Malibu, Alero, Cobalt, HHR, G5 and Ion. This is a used part, so match it against the shell you removed by tooth count, spline count and overall shape. If you want us to double-check, send the year and VIN. Every part we carry for this unit is on our 4T40E transmission page.
| Fits | 4T40E |
| Part type | Reaction Shell |
| Condition | Used |
| Brand | GM |
| Ships | From the USA |
| Warranty | 1-year |
Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
The photo shows a windowed shell with the sun gear hub in the center, which is the reaction sun shell. The 4T40E also has a separate reaction carrier shell, so compare the photo with your removed part before ordering.
The listing is for the 4T40E. The 4T45E shares much of the design, but match tooth count, splines and shape against your old shell or send us your year and VIN to check.
Replace the thrust bearings on both sides, the related bushings, and the frictions and seals from a rebuild kit. Inspect the planets and input sprag, since damage there often goes with a failed shell.
GM approves Dexron VI for transmissions that originally specified earlier Dexron fluids, including the 4T40E.
It is a solid steel hard part, so a clean used shell with good teeth and a good hub surface is a sound repair. Inspect it on arrival and confirm it matches before you start assembly.
