TH350C - How to Set Up the Lockup

[Houston54]

I have seen several threads asking how to wire up the lockup feature of the TH350C without having to purchase one of the expensive kits available from several sources.

The following are the AC Delco part numbers for the original components used for this transmission type.

Vacuum Switch - AC Delco # 212-331, GM # 14032087 (Current Pricing at XL Auto Parts $35.31)
Brake Pedal Switch - AC Delco # D850A, GM # 25524845 (Current Pricing at XL Auto Parts $11.32)
Vacuum Check Valve - AC Delco # 214-479, GM # 14020691 (Current Pricing at XL Auto Parts $19.91)

The plug for wiring to the vacuum switch is not available new to my knowledge and I could not find one at the local salvage yard. To make the connection I soldered the wires directly to the connector lands on the switch using shrink tubing to provide some strain relief protection.

One of the wires from the vacumm switch goes to a keyed 12V source while the other wire goes to the brake switch.

The brake switch has four poles on it. Two are for the lockup function and the other two are for the tail light circuit. I had to figure out which was which was trial and error. Once you get that figured out and connect the switched 12v from the vacuum switch you will need to run aother wire from the other pole down to the solenoid switch on the transmission. The solenoid switch the rebuilder put in my trans only has one pole on it as the original is difficult to impossible to find. The replacement switch is from a later model GM lockup trans. It may be the 200R4 switch but not sure. If I get by the rebuilders shop again I will ask.

The other side of the vacuum switch consists of a male vacuum connection which I tubed to the intake manifold vacuum tree. The small check valve was inserted between the switch and the manifold.

That is it. Total parts cost is $66.54 plus tax of course.

I tried sourcing these parts directly from the local Chevy dealer and found the prices much much higher. Your results may vary.

I mounted the vacuum switch on my firewall and to date the system has performed flawlessly.

Hope this helps someone else out there.