TH400 Clutch Module 1965-1995, new and ready to install. Fits the TH400. Ships fast from the USA.
A Turbo 400 that flares between gears, slips when you lean on it with a trailer behind, or comes out of the pan with black, burnt-smelling fluid has usually cooked its friction plates. This listing is the frictions side of that repair: Alto's high-performance TH400 friction module, part number A34119HP (industry number 031752HP), for 1965-1995 units. It is a new aftermarket module, built for a rebuild where you want more holding capacity than stock paper, whether the transmission sits behind a big-block Chevy truck, a Buick, Olds or Cadillac, a Jeep, or a Jaguar, Rolls-Royce or Bentley that used the same GM gearbox. When Alto stock is short, the equivalent Allomatic or Raybestos high-performance module may be supplied in its place.
The TH400 makes its three forward gears and Reverse with three multiple-disc clutches, two bands and a compound planetary gearset. The forward clutch is applied in every forward gear, the intermediate clutch comes on for Second, and the direct clutch comes on for Third and Reverse. Each clutch is a stack of lined friction plates alternated with steel plates; oil pressure pushes a piston into the stack and the plates lock together. On a typical GM stack that means five composition plates in the forward clutch, five in the direct clutch and three in the intermediate clutch (the light-duty BK version used four in the forward and direct packs). When the lining glazes, flakes or wears thin, piston travel grows, the clutch takes longer to lock, and the slip turns into heat that ruins the fluid and the next set of plates.
Check the fluid level first, then put a gauge on the line pressure tap. GM's diagnosis charts for this transmission list a leaking vacuum modulator, a sticking modulator valve, a plugged filter or a stuck pressure regulator valve as causes of the same slip, and none of those are fixed by new plates. If pressure is good and one gear slips, the plates in that clutch are worn or a piston seal or check ball is letting the apply leak off. Our TH400 common problems and fixes guide walks through the gauge readings, and TH400 delayed engagement covers the slow-to-Drive complaint.
This module is listed for TH400 transmissions from 1965 through 1995, including GM car and truck applications and the Jeep, Jaguar, Rolls-Royce and Bentley units that shared the GM case. Plate counts changed between some models over that span, so lay your old frictions next to the new ones and compare the count, tooth style and thickness before you assemble anything. If you are not sure which TH400 you have, send your year, make, model and engine and we will check it before it ships. For a first-year 1964 unit, see the 1964 TH400 clutch pack, and browse every part we carry for this unit on the TH400 parts page.
Most rebuilders install these plates as part of a full seal and gasket job; the TH400 overhaul kit for 1965-1998 or the TH400 master rebuild kit covers the seals, gaskets and sealing rings this module does not include.
| Fits | TH400 1965-1995 |
| Part type | Clutch Module |
| Condition | New |
| 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.
It is Alto's high-performance friction module A34119HP (industry number 031752HP), the lined clutch plates for the TH400 clutch packs. Steel plates, seals, gaskets and bands are not part of the module. If Alto is out of stock, the matching Allomatic or Raybestos high-performance module may be shipped instead.
The module is listed for 1965-1995 TH400 units, and a 1979 truck falls in that range. Compare your old plates for count, teeth and thickness before assembly, or send your year, model and engine and we will confirm it first.
Second gear uses the intermediate clutch plus the intermediate one-way clutch. GM also lists a missing constant bleed orifice in the center support, a stuck 1-2 accumulator valve, a loose center support bolt, a missing intermediate clutch case plug and low line pressure as causes of a 1-2 slip, so check pressure and inspect those parts when the unit is apart.
Often yes. GM's guidance is to wipe the steels dry and reuse them if the surface is smooth with an even color, and to replace any steel with heat spots or scuffing. Do not judge the frictions by color alone; look for pitting, flaking, glazing, cracking or embedded metal.
The TH400 takes Dexron automatic transmission fluid. Soak the frictions in it for at least 30 minutes, lubricate the steels with it during assembly, and fill the transmission with the same fluid.
