Rebuild kit for 1969-1986 GM TH350 three-speeds with the frictions, steels, gaskets, seals and O-rings a full teardown needs.
Rebuilding a GM Turbo-Hydramatic 350 that has started slipping, shifting late and soft, or refusing to take Reverse until it warms up? The SM-9 is the standard ATP master repair kit for the TH350 and the TH350C lockup version, 1969-1986. It is the kit for a builder who already has the unit on the bench and wants every clutch plate and soft seal replaced without paying for extras: friction plates, steel plates, the pan gasket, the case and pump gaskets, rubber lip seals, metal-clad seals, sealing rings and the O-ring set. Hard parts, the band, the filter, bushings and the converter are not included, which keeps the price below our Plus version and lets you pick your own filter and bushing set.
The TH350 uses a compound planetary gearset controlled by the forward clutch, the intermediate clutch, the direct clutch and the low and reverse clutch, plus the intermediate overrun band and two roller clutches. Each clutch is a piston in a drum or in the case, sealed with lip seals and squeezing a stack of friction and steel plates. The rotating drums get their apply oil through sealing rings on the pump hub and the governor, and the case, pump and valve body seal to each other through paper gaskets. When a TH350 slips, the root cause is almost always one of those soft parts: burned or glazed plates, a hardened piston seal, a worn sealing ring that leaks apply pressure, or a gasket that has shifted and opened a cross-leak. The SM-9 replaces that whole category at once, so you are not reusing a 40-year-old seal next to new plates.
A gauge on the line pressure port tells you whether the problem is pressure or a clutch. Low pressure in every range points to the pump, the pressure regulator, a plugged filter or the vacuum modulator; normal pressure with a slip in one gear points to that gear's clutch pack or its seals. GM's TH350 charts list each symptom by unit, and our TH350 common problems guide pairs those causes with the bore wear that a seal kit alone will not cure. If the noise or pressure loss is up front, check the TH350 pump failure guide as well, because a scored pump body or worn bushing will eat a new set of seals.
Listed for GM TH350 and TH350C transmissions from 1969 through 1986, covering Chevrolet, GMC, Pontiac, Oldsmobile and Buick rear-drive cars and light trucks. The lockup TH350C, built from late 1979, shares the kit. Plate counts in the intermediate and low-reverse packs varied with engine and vehicle, so count your old plates as you take each pack apart and use the matching number from the kit. To check fitment before ordering, send us your year, vehicle and VIN or the ID tag numbers from the case. See every part we carry for this unit on the TH350 transmission page.
If the bench check shows a worn intermediate roller clutch, a scored piston bore or a cracked direct drum, add a remanufactured TH350 direct clutch drum with sprag to the order. For a street or tow build, a governor shift point kit lets you move the full-throttle shift points to suit the engine.
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Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
No. The SM-9 listing excludes the filter, the band, bushings, hard parts and the torque converter. If you want the filter in the same box, the ATP SMS-9 Plus kit we carry includes one.
Yes. The kit includes both friction plates and steel plates, so glazed or warped steels can be replaced along with the frictions.
Yes. The SM-9 is listed for the TH350 and TH350C from 1969 to 1986. The lockup solenoid, wiring and converter are separate parts.
Inspect it. The intermediate overrun band only applies in manual second, so it often survives, but replace it if the lining is burned, cracked, flaking or worn to the rivets.
A filter, a bushing set on high-mileage units, and any worn hard parts found on the bench such as the intermediate sprag, a scored pump or a cracked drum. Many builders also add a shift kit.
