Wires the torque converter clutch on a swapped GM 700R4 or 200-4R so it locks up in high gear off a vacuum switch, with a manual override toggle.
Swapped a 700R4 or 200-4R into a street rod, a muscle car or an older truck that never had an engine computer, and the converter will not lock at highway speed? That is normal for these transmissions when nothing commands the lockup clutch. TCI part 376600 is a complete wiring package that does the job inside and outside the case: it replaces the factory internal harness, adds a fourth gear pressure switch on the valve body, and uses an adjustable engine vacuum switch so lockup only happens at steady cruise. It is also the kit TCI points to when the original computer is removed from a pre-1993 GM vehicle running one of these units.
The converter clutch is applied by a solenoid that sits on the pump side of the case. Power it and ground it, and oil is routed to lock the converter; cut either side and the converter goes back to fluid drive. TCI wires the circuit so the solenoid only completes when three things line up: the key is on (red wire, switched 12 volts), the transmission is in fourth (the normally open pressure switch closes on fourth gear oil), and the engine is not under load (the normally open vacuum switch closes once vacuum is above roughly 8 to 10 inches). Downshift out of fourth or open the throttle far enough to drop vacuum, and the converter releases.
A converter that shudders as it applies, a slipping 3-4 clutch or a unit that never reaches fourth are hydraulic problems this kit cannot fix. Our 700R4 common problems guide and valve body testing guide cover those.
Make sure the transmission upshifts into fourth on its own first, because the pressure switch will never close otherwise. Then pull the pan and look at the solenoid. TCI's kit reuses the factory solenoid only if it is a two-wire design; a one-wire solenoid cannot be used, and TCI lists GM 8654126 as the correct two-wire replacement. Also confirm the converter is a lockup converter, since some aftermarket stall converters are not. If the vehicle still has its original computer controlling lockup, you do not need this kit.
Fits the GM 700R4 (TH700-R4) and 200-4R (2004R). TCI includes wiring diagrams for a street/strip 700R4, a 700R4 with a full manual valve body, and the 200-4R, so the pressure switch location depends on your valve body. The pan gasket is 700R4 only, so 200-4R owners should buy their own gasket. TCI notes some 200-4R case connectors will not latch the new harness; GM case connector 8634383 fixes that. Our 200-4R vs 700R4 guide helps confirm which unit you have, and every matching part is on our 700R4 collection page. Unsure? Send us the vehicle year and VIN or the transmission tag.
With the pan off, it is a good time to check the valve body and the pump, where the solenoid lives; a worn unit is covered by our 700R4 pump 1987-93 listing and the pump failure guide.
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Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
No. It reuses the factory solenoid as long as it is a two-wire type. A one-wire solenoid cannot be used; TCI lists GM 8654126 as the two-wire replacement.
TCI's instructions call for a ported vacuum source on the carburetor or throttle body. If lockup engages erratically, move it to a manifold vacuum source.
Yes, with a toggle switch you supply. Grounding the green wire through a dash switch locks the converter in 2nd, 3rd or 4th, and a second switch in the red feed turns the whole system off.
Yes. Buy a 200-4R pan gasket separately because the one in the kit is 700R4 only, and if the harness will not latch in the case, TCI recommends GM connector 8634383.
Run the switched 12 volt feed through a normally closed brake pedal switch before it reaches the red wire. The converter unlocks the moment the pedal is pressed.
