TH400 Overhaul Kit 1965-98, new and ready to install. Fits the TH400. Ships fast from the USA.
Sometimes a Turbo 400 does not need new clutches at all. It leaks from the pan and pump, it is slow to go into gear on a cold morning, or it is coming apart for a different reason and you just need every seal and gasket to put it back together. This is the kit for that: a Transtec overhaul kit for the GM TH400, 1965 through 1998. Transtec is one of the long-standing names in rebuild soft parts, and this is the gasket and seal core that most shops build a 400 around.
This is a soft-parts kit only. There are no frictions, steels, bands, bushings, filter or modulator in the box. If your teardown shows burnt clutches, step up to the TH400 performance master rebuild kit or the TH400 banner rebuild kit that adds frictions.
Every shift in a TH400 is hydraulic. The pump sends line pressure through the valve body to the forward, direct and intermediate clutch pistons and the band servos. The lip seals on each piston are what let that pressure push the clutch pack together. The metal sealing rings seal oil passing from the stationary case and center support into spinning drums and shafts. When those seals harden and shrink with age and heat, pressure leaks off before it reaches the piston. The result is a pack that applies slowly or not fully, which you feel as delayed engagement, a slip during the shift, and eventually burnt frictions. The gaskets and metal clad seals handle the outside of the unit: the pan, pump, extension housing and the front and rear seals where the converter hub and driveshaft yoke pass through.
Drop the pan. Fluid that is red and smells normal, with only light gray sludge on the magnet, means the clutches are probably fine and the problem is sealing. Brown fluid with friction material means you need frictions too. Our TH400 delayed engagement guide covers the cold-engagement symptom in detail, and TH400 common problems and fixes helps you rule out the vacuum modulator and valve body before you open the case.
The kit is listed for the GM TH400 from 1965 to 1998, including the 3L80 version used in later GM trucks and vans. That range covers early car units and the later truck and motorhome units, which differ in clutch counts and some hard parts but use the same basic seal layout. Check your transmission ID plate, and if your unit is an early switch-pitch or has been converted with aftermarket drums or pistons, send us the year and VIN before ordering. See every TH400 part we carry on the TH400 parts page.
Clean every bore before installing the new lip seals, and lubricate them with assembly gel or ATF so they do not roll or cut going into the drum. Install the metal sealing rings with their ends hooked correctly and check that each turns freely in its groove. Air check every clutch and servo circuit before the valve body goes on: you should hear a firm thud as each piston applies. Torque the pump bolts evenly with the new washers. If the front seal leaked because the bushing behind it is worn, replace the bushing too, or the new seal will fail quickly. Refill with Dexron-type ATF. If your unit leaks only externally, the TH400 external reseal kit covers the outside seals without a full teardown.
| Fits | TH400 1965-98 |
| Part type | Overhaul Kit |
| Condition | New |
| Brand | OEM |
| Reference | 81000112 |
| 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 kit: paper and metal gaskets, piston lip seals, O-rings, sealing rings, metal clad seals and pump bolt washers. Frictions, steels, bands, bushings and the filter are sold separately.
It is listed for GM TH400 transmissions from 1965 to 1998, including the 3L80 name used on later units. Send us your year and VIN if you are unsure.
Only if the clutches are still in good shape. If the pan shows friction material or the fluid is burnt, the clutch packs need replacing along with the seals.
External leaks at the pan, tail housing or selector shaft can often be fixed in the vehicle with an external reseal kit. A front pump seal leak needs the transmission out but not a full rebuild.
A seal driver, snap ring pliers, a clutch spring compressor and an air nozzle for circuit checks cover most of the job. Use assembly gel on the seals.
