TH400 Input Drum 1964-1990, remanufactured and ready to install. Fits the TH400. Ships fast from the USA.
If your Turbo 400 moves in Reverse but will not pull in Drive, takes a long time to engage when you drop it out of Park, or slips in every forward gear while third still feels firm, the forward clutch is the first place to look. This listing is a TH400 forward drum assembly, the input drum that carries the turbine shaft, and it comes built up rather than bare: the housing with its turbine shaft, five new Alto High Energy friction plates, six reconditioned steel plates, an aluminum piston, the forward clutch hub, the direct clutch hub, the 16 release springs, the spring retainer and the snap rings and washers. It is a reconditioned used assembly that can go into any 1964-1990 TH400, so it suits a truck, motorhome or muscle car rebuild where the original drum is cracked, scored or missing.
The TH400 forward clutch housing is the first rotating member behind the pump. The turbine shaft is pressed into it, so it turns at converter turbine speed all the time the engine runs. When the forward clutch applies, the plates lock the housing to the forward clutch hub, which is splined to the mainshaft and carries power back into the planetary gearset. That clutch is on in every forward range, so a forward clutch that cannot hold pressure gives you no Drive, or a weak, slipping Drive, Second and Low while Reverse (which does not use it) still works. The same housing also carries the direct clutch hub on its back side, so it is part of the power path into the direct clutch in third gear.
Apply oil reaches the piston through the pump cover hub and its sealing rings, then through drilled passages in the housing. A check ball in the housing lets oil exhaust when the clutch releases. GM's 1975 manual lists a stuck or missing check ball, a cracked piston, damaged seals, low line pressure and restricted feed passages as the causes of burned forward clutch plates.
Check the fluid level and the modulator first, because a leaking modulator diaphragm can pull fluid out of the unit and imitate a clutch failure. Then put a pressure gauge on the case. Low pressure in Drive with good pressure in Reverse points toward the forward circuit, including the pump hub sealing rings, not just the drum. Our TH400 delayed engagement guide walks through that test order, and the TH400 pump failure guide covers the pressure numbers and the pump side of the circuit. With the unit apart, air-check the forward piston, inspect the housing for scoring and open oil passages, make sure the check ball moves freely, and look at the turbine shaft splines and lube holes.
This assembly fits TH400 transmissions from 1964 through 1990, including GM cars, trucks and motorhomes of that era. The turbine shaft is the part to check most closely: shaft length and spline count must match the converter you run, and early switch-pitch units used their own pump and converter combination, so lay your old shaft beside this one before you install it. If you are unsure, send us your year and VIN or the transmission ID plate and we will confirm it. You can see the rest of our parts for this unit on the TH400 parts page.
A burned forward clutch usually leaves debris through the whole unit, so plan on a seal and gasket set at minimum. The TH400 overhaul kit covers the seals and gaskets, and if the direct drum is also damaged, our TH400 direct clutch drum is the matching piece. The TH400 common problems guide lists the other wear points to inspect while you are inside.
| Fits | TH400 1964-1990 |
| Part type | Input Drum |
| Condition | Remanufactured |
| 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.
The forward clutch housing with turbine shaft, five new Alto High Energy frictions, six reconditioned steels, an aluminum piston, the forward clutch hub, the direct clutch hub, 16 release springs, the spring retainer and the snap rings and washers. Seals, gaskets, the pump and the direct drum are not included.
Yes. On the TH400 the turbine shaft is pressed into the forward clutch housing, so the forward drum is the input drum. It is different from the direct clutch drum, which sits behind it and is wrapped by the front band.
It will if the forward clutch is the cause. Reverse does not use the forward clutch, so no Drive with good Reverse often means burned forward plates, a cracked piston, bad seals or a stuck check ball. Check fluid level, the modulator and line pressure first, since a weak pump or broken pump hub sealing rings cause the same complaint.
The assembly is listed for any 1964-1990 TH400, and a 1972 truck falls in that range. Compare the turbine shaft length and splines with your old one, or send your year and VIN and we will check it before it ships.
The TH400 uses Dexron automatic transmission fluid. Soak the frictions in Dexron before assembly and fill the unit with the same fluid after installation.
Yes. Front unit end play is measured at the turbine shaft after the pump is installed. GM lists .003 to .024 inch, adjusted with the selective washer between the pump cover and the forward clutch housing.
