TH400 Shift Kit 1964-98, new and ready to install. Fits the TH400. Ships fast from the USA.
This is the Fairbanks TransAction valve body kit for the GM Turbo 400, a four-stage performance kit that lets one box cover a work truck, a street and strip car or a full manual race setup. If your 400 drags out the 1-2 shift, slides into third with a load on, or you want gear control without buying a complete manual valve body, this kit is built for that job. The listing title reads 1964-98, but the kit itself is made for the 1965-on 400 valve body, and the maker states it works in both 6 and 7 check ball cases. Read the fitment section before ordering for a 1964 unit.
The Turbo 400 has no shift solenoids. Shift timing comes from governor pressure fighting throttle and modulator pressure at the shift valves, and shift feel comes from how fast oil can reach each clutch through the separator plate. The TransAction kit changes the second half of that equation. It supplies new separator plates and gaskets with recalibrated feed holes plus the springs and small valve parts shown in the photo, so the intermediate and direct clutches lock quicker and spend less time slipping. The result is a positive, firm shift instead of a long flare. Passing gear is retained, and the shift points are adjustable.
The four stages are what set this kit apart from a one-step shift kit:
Those complaints overlap with worn clutches, a leaking vacuum modulator and pump wear, the three classic TH400 failures. A shift kit is not a cure for burned frictions.
Start with the fluid level and condition, then check the modulator for a ruptured diaphragm (fluid in the vacuum line is the giveaway) and put a gauge on the line pressure tap. Soft shifts with correct pressure and clean fluid point at valve body calibration, which is what this kit changes. Low pressure in every range points at the pump or pressure regulator instead. Our TH400 valve body testing guide walks through those checks, and the TH400 common problems guide helps separate a calibration problem from worn hard parts.
The kit fits the GM TH400 from 1965 on, in both 6 and 7 check ball cases, covering the cars, trucks and motorhomes that ran the 400 and later 3L80 service units. The 1964 TH400 used a different first-year valve body that needs its own kit, so if your unit is a 1964, do not order this one. It does not fit the electronic 4L80E. If you are unsure which 400 you have, send us the year and VIN or a photo of the valve body and separator plate before ordering. See every 400 part we carry on the TH400 parts page.
Stages 3 and 4 are firm. Street drivers and tow rigs are usually happiest at Stage 1 or 2.
| Fits | TH400 1964-98 |
| Part type | Shift Kit |
| 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.
No. The kit is made for the 1965-on Turbo 400 valve body. The 1964 unit used a first-year valve body that takes a different kit. Send us a photo of your valve body if you are not sure which you have.
Yes. The kit is stated to work in both 6 and 7 check ball cases. Follow the instructions for check ball placement for your stage.
Stage 1, Heavy Duty, is meant for towing, motorhomes and work trucks. It shortens the shift to cut clutch slip without the harshness of the competition stages.
No. The kit retains passing gear. Passing gear still needs a working detent solenoid or switch circuit, so check that if you never get a forced downshift.
Yes. The valve body and separator plate are serviced through the pan opening. You only need the transmission out if the clutches also need replacing.
The TH400 takes Dexron-type ATF. Refill to the full mark warm and recheck after the first drive.
