TH350 Clutch Drum 1969-1980, new other (see details) and ready to install. Fits the TH350. Ships fast from the USA.
When a Turbo 350 shifts 1-2 and then never finds third, slips on the 2-3 shift, or will not back up, the direct clutch is often the reason, and a cracked or worn direct drum means the frictions alone will not fix it. This is a genuine GM direct clutch drum, part number 8640308, new old stock that has never been installed. The box is worn from storage and the drum shows minor flash rust, but it is an unused factory part for TH350 transmissions from 1969 into the early 1980s.
GM calls the direct clutch the 2-3 clutch. It is applied in third gear and in Reverse, so one failed drum can take out both. The drum holds the piston, the 17 return springs, and the stack of lined and steel plates, and its hub carries the bushing that rides on the pump stator shaft. Oil reaches the piston through the three hook-type rings on the pump hub, and a check ball in the piston lets the apply oil exhaust when the clutch releases. The outside of the drum hub also acts as the inner cam for the intermediate overrun roller clutch, the one-way clutch that holds for second gear. That makes the drum surface just as important as the plates inside it.
GM's diagnosis chart lists the pump hub direct clutch rings and the direct clutch piston seals and check ball as causes of no 2-3 shift, so a pressure test comes first: low pressure in every range is a pump or regulator problem, not a drum problem. With the transmission apart, air-check the direct clutch, then inspect the drum for cracks around the piston bore and spring retainer, scoring in the bushing bore and a worn or pitted roller track on the hub. If the drum checks out, a set of frictions and seals may be all it needs. See TH350 common problems and fixes for the no 2nd and no Reverse diagnosis, and TH350 valve body testing to rule out a stuck 2-3 shift valve.
GM 8640308 fits the TH350 family used in most rear-drive GM cars, light trucks and vans from 1969 through the early 1980s, from the Camaro, Chevelle, Nova and Impala to C/K pickups and BOP cars. TH350 drums vary: there are narrow and wide direct drums, lockup and non-lockup units, and different intermediate overrun setups. Compare this drum against yours for width, spline count and the hub that carries the intermediate overrun clutch, or check the part number on your old drum. The intermediate roller clutch and outer race are separate parts, so plan to reuse yours or replace them. If you are unsure, send us your year, vehicle and VIN and we will confirm before it ships. More drums and hard parts are on the TH350 parts page.
A fresh drum deserves fresh friction material: the ATP SMS-9 TH350 master repair kit covers the plates and seals, and the TH350 sprag clutch is worth replacing if the old overrun clutch is worn.
| Fits | TH350 1969-1980 |
| Part type | Clutch Drum |
| Condition | New Other (See Details) |
| Brand | GM |
| Reference | 8640308 |
| Ships | From the USA |
| Warranty | 1-year |
Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
It is the direct clutch drum, also called the 2-3 clutch drum, GM part number 8640308. It is new old stock with a storage-worn box and minor flash rust.
Plan on the drum only. The intermediate overrun roller clutch and its outer race are separate parts, so reuse yours if they are in good shape or replace them.
The direct clutch is applied in third and Reverse, so a failed drum typically causes no 2-3 shift, a slipping 2-3 shift, or no Reverse. A worn hub race can also cause slipping in second.
TH350 drums vary in width and setup, and lockup TH350C units used some different parts. Compare the drum with yours or send us your year and VIN to confirm before ordering.
New direct clutch frictions and steels, the three piston seals, and the pump hub sealing rings that feed the clutch. Check the stator shaft and pump bushings while the pump is out.
