200-4R Input Drum 1976-90, new and ready to install. Fits the 200-4R. Ships fast from the USA.
A 200-4R in a Grand National, Regal, Monte Carlo, Cutlass or Caprice that suddenly pulls only in first, will not upshift no matter how long you hold it, and has lost Reverse at the same moment is a classic case of a failed input shell. This listing is a new input drum shell, often called the sun gear shell or sun gear drive shell, for the THM200, 200C and 200-4R from 1976 to 1990. It is the bowl-shaped stamped shell with drive tabs around its rim and a splined center, not the forward clutch drum with a shaft that some catalogs also call an input drum.
The 200-4R is a THM200 gear train with an overdrive section added in front. In that gear train the shell links the direct (high/reverse) clutch drum to the rear sun gear: tabs on the shell's rim engage notches in the drum, and the splines in the center lock onto the sun gear, with a snap ring on the sun gear holding the shell in place. Rebuilders explain its job this way. In second, the intermediate band grabs the drum, so the shell holds the sun gear still. In third and overdrive, the applied direct clutch turns the sun gear through the shell. In Reverse, the direct drum drives the sun gear through the shell to produce the reverse ratio.
First gear is the exception. It runs through the forward clutch and the low roller clutch and does not need the shell, which is why a shell that has stripped its splines or broken its tabs leaves a car that drives off normally in first and then goes nowhere else.
Several cheaper faults can mimic a lost shell, so rule them out. A stuck governor or a TV cable out of adjustment can leave the car in first, and B&M's 200-4R troubleshooting chart lists line pressure, TV cable and valve body problems among the causes of slips and no-shift conditions. If first works, the car still upshifts on a gauge-confirmed normal line pressure, and Reverse still pulls, the shell is unlikely. If first works but every gear that needs the sun gear is gone, it is a strong candidate. Our 200-4R no reverse guide and 200-4R common problems and fixes walk through the in-car checks. A bad shell is confirmed only with the unit apart: inspect the center splines, the drive tabs and the mating rear sun gear.
This shell is listed for the 1976-1990 THM200, 200C and 200-4R, the family that shares this part of the gear train. The 200-4R itself was built from 1981 to 1990 for rear-wheel-drive GM cars. Before installing, check that the tab count and spacing match your direct drum, that the center splines slide onto your rear sun gear, and that the shell depth matches your old one. Send us your year and VIN, or a photo of your old shell, if you want us to confirm it. The rest of our parts for this unit are on the 200-4R parts page. Looking for the forward drum with its input shaft instead? That is our 1981-1990 200-4R forward drum.
| Fits | 200-4R 1976-90 |
| Part type | Input Drum |
| Condition | New |
| 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. This part is sold as the input drum shell, and it is the sun gear (drive) shell that connects the direct clutch drum to the rear sun gear. It is not the forward clutch drum with the input shaft.
Second, third, overdrive and Reverse all need the sun gear held or driven through this shell. First runs through the forward clutch and the low roller clutch, so a shell with stripped splines or broken tabs leaves first as the only working gear. Rule out the governor and TV cable before tearing the unit down.
It is listed for 1976-1990 THM200, 200C and 200-4R. Compare the tab layout, center splines and depth with your old shell before installing.
The listing does not state a heat-treat grade, so we do not claim one. If you are building a high-torque or boosted car, check it with a file or pick before installing, or ask us before ordering.
Inspect and usually replace the rear sun gear if its splines are chipped, plus the thrust washers and bearings around it. Most builders install a master rebuild kit at the same time.
