TH350 Overhaul Kit 1969-1980, new and ready to install. Fits the TH350. Ships fast from the USA.
Tearing down the Turbo 350 out of a 1970s Chevelle, Nova, Camaro, C10 or Buick and need every gasket and seal in one box? This is overhaul kit KP35900B, packed for the TH350 and the TH250 from 1969 through 1980. It is the soft-parts half of a rebuild: the pan gasket, the valve body and pump gaskets, the clutch piston seals, the O-rings and the sealing rings that feed oil to the rotating drums. It does not include friction plates, steel plates, a band, bushings or a filter, so plan to buy those separately if the teardown shows you need them.
A TH350 is fully hydraulic. The pump makes line pressure, the valve body routes it, and every clutch apply depends on rubber holding that oil inside a piston bore. The forward, direct, intermediate and low/reverse pistons each ride on lip or lathe-cut seals, and the drums receive their oil through sealing rings that spin against the pump stator shaft and the case. After forty-plus years those seals harden and take a set. Oil that should push a piston leaks past it instead, and the clutch fills slowly or never clamps hard. This kit replaces every one of those sealing points at once, so the fresh clutches you install are not working against old rubber.
Seals are only part of the picture. A worn pump bushing, a worn boost valve sleeve or a scored servo bore will drop line pressure just as badly, and new seals will not cure those. Note which ranges are late and whether it changes hot or cold; our TH350 delayed engagement guide sorts the causes by that pattern. If the trouble is a leak rather than a slip, trace it with the case clean and dry before you pull anything. The TH350 leak-point guide walks through GM's own list, because a filler tube or modulator drip often shows up at the back of the case.
This kit is listed for TH350 and TH250 transmissions from 1969 to 1980. The TH350 arrived for the 1969 model year, and GM added the TH350C lockup version late in 1979. If your unit has an electrical connector on the left side of the case, it is a lockup TH350C, so check that the gasket and seal count matches what you pulled out, or send us your year and VIN before you order. For a 1981-1986 lockup unit, look at the 1969-1986 TH350 and TH350C overhaul kit. Every TH350 kit and hard part we carry is on the TH350 parts page.
Soak the lip seals in ATF before assembly, install each piston with a seal protector or a feeler gauge to walk the lip into the bore, and coat the sealing rings with assembly gel so they stay centered while the drums go in. Air-check each clutch and the servo before the valve body goes on. Lay the valve body gasket over the spacer plate and match every hole before you torque the bolts. GM's 1976 truck service supplement calls for 130 in-lb on the pan bolts with no sealer, and the old pan rail should be checked flat. Refill with a current licensed Dexron VI, which is back-serviceable to the older Dexron spec.
An overhaul is the right time to replace the wear parts too. Most rebuilders install new frictions and steels with the seals; our TH350 clutch module covers that side. Swap in a new adjustable vacuum modulator while the case is open, since a ruptured diaphragm causes harsh shifts and burns fluid.
| Fits | TH350 1969-1980 |
| Part type | Overhaul Kit |
| Condition | New |
| Brand | OEM |
| Reference | KP35900B |
| Ships | From the USA |
| Warranty | 1-year |
Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
No. It is a gasket and seal overhaul kit: pan, pump and valve body gaskets, piston seals, O-rings, sealing rings and the front and rear seals. Frictions, steels, band, bushings and filter are separate.
The kit is listed for 1969-1980 TH350 and TH250 units. Lockup TH350C units started late in 1979, so compare the kit to your old gaskets and seals or send us your year and VIN before ordering.
Yes, the kit is listed for both the TH250 and TH350 for 1969-1980.
A licensed Dexron VI ATF. It is back-serviceable to the Dexron and Dexron II that GM originally specified for the TH350. Set the final level on the dipstick with the engine running at operating temperature.
No. Install the pan gasket dry on a flat rail and torque the bolts evenly to about 130 in-lb. Sealer can break off and plug the filter or valve body.
