Reprograms the valve body on a 1981-91 GM TH350C lockup transmission for firm shifts and manual backshifts into 2nd and 1st at any RPM.
If you are building a lockup Turbo 350 for a street car, a hot small block or a truck that tows, and the stock shift is slow, mushy and burning the direct clutch, this is the kit TransGo designs for it. The 350C-1&2 is TransGo's Gear Command reprogramming kit for the GM Turbo Hydra-Matic 350C. TransGo lists it for 1981-1991 TH350C units only, and says it does not fit the 250C. It is part number TGO350C-1-2 and is made in the USA.
A stock TH350C is calibrated for a quiet, soft shift. The clutches slip for a long time on every change, and that slip is heat. TransGo says the weak point in this transmission is the direct (2-3) clutch, and that this kit triples its holding power. The kit reworks the valve body and separator plate so the clutches apply quicker and harder, which shortens the overlap between gears. The Gear Command part is about control. The transmission still upshifts on its own in Drive, but in the manual ranges it holds first and second to any rpm and backshifts to second and first at any speed. TransGo rates the kit for small blocks up to 550 horsepower, for street use, towing or full race.
A shift kit firms up a healthy transmission. It does not fix one that is already slipping. Check the fluid level and condition, the modulator and vacuum line, and the detent cable first. A worn 1-2 accumulator or intermediate servo bore can also cause slip and low line pressure. Our TH350 shift quality guide covers the accumulator and modulator checks, and the TH350 valve body testing guide explains how to tell a worn bore from a calibration problem. A gauge kit like our vacuum and pressure gauge kit lets you read line pressure before and after.
This kit is for the TH350C lockup transmission only. The non-lockup TH350 takes a different TransGo kit, and the 250C is excluded. Novak identifies the TH350C by its lockup converter and the electrical connector on the left side of the case. Novak dates the C version from late 1979, while TransGo lists the kit for 1981-1991, so check your case rather than going by model year alone. If you are not sure what you have, send us your year, vehicle and a photo of the left side of the case. Other TH350 and TH350C parts are on the TH350 parts page.
If the transmission is apart, pair the kit with a TH350 banner rebuild kit so it goes in with fresh frictions. A TH350 clutch module works too if the hard parts are good.
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Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
No. TransGo lists the 350C-1&2 for the TH350C lockup transmission only, and it does not fit the 250C. A non-lockup TH350 takes a different kit. Look for the lockup connector on the left side of the case to confirm what you have.
Yes. The reprogramming is done on the valve body and separator plate, which come out after you drop the pan. Many people do it during a rebuild, but you can do it in the vehicle with hand tools if the clutches are healthy.
It shifts firmer than stock, because that is how it cuts slip time. TransGo pitches it for street, towing and race use, and the transmission still upshifts on its own in Drive. If you want the mildest shift, follow the street steps in the instruction sheet.
In the manual ranges the transmission holds first and second to any rpm and backshifts to second and first at any speed when you move the selector. In Drive it still shifts on its own.
Not if the clutches are burned. A shift kit protects good clutches but will not repair worn frictions, a worn accumulator bore or a leaking modulator. Diagnose those first and replace worn frictions before installing the kit.
Dexron ATF, the factory spec for the TH350 family. Refill after the pan drop and set the level with the fluid at operating temperature.
