I realize running an automatic is not attractive to everyone but sometimes it is the bestor most cost effective option. If that applies to your project and you just happen to have a TH350 with the lockup feature sitting on the floor of the garage here is how to get that lockup feature working. Of course you do not have to wire up the lockup to make a TH350C work as a regular TH350 but since most of my miles are over longer distances (This is Texas) I elected to see if the lockup would help. So far I can't complain even though it may not be as high tech as a 700R or other OD auto. This information is an alternative to purchasing one of the expensive hookup 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 (Quoted price was $35.31) Brake Pedal Switch - AC Delco # D850A, GM # 25524845 (Quoted price was $11.32) Vacuum Check Valve - AC Delco # 214-479, GM # 14020691 (Quoted price was $19.91) Total cost = $66.54 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. The prices I have added above were quoted to me by XL Auto Parts. The pricing from the dealer was much much higher. I would imagine that NAPA stores could source these items as well. Your results may vary. I mounted the vacuum switch on my firewall and to date the system has performed flawlessly. Maybe my next project will be a gear jammer. Hope this helps someone else out there.
What years/models were equiped with the 350-c? I had always been under the impression that the lockup 350 was stupid rare,,, a 1 year only deal that was quickly replaced with the 200-R4
The TH350C was used in 80-83 camaro/firebirds, 80-87 caprice and similar, 82-84 malibus, 78-82 trucks/vans. Not that rare but it does have a un-deserved reputation as being weak. Not what you might want to run a high HP/torque motor in front of but plenty strong for most rod applications. I will say this is my first use of a TH350C and the rear gear I have been running (2.41) is not suitable for it. Currently performing an axle swap which will include a 3.42 posi. The earliest I know a 200R4 being used is in the 84 G-bodys but may have been used in other models earlier than that.
TH350c's were also used in 80/81 C3 Vettes. I didn't even know they existed 'till I got mine home from the junkyard! I didn't remove the engine and trans so I didn't get any of the parts from the donor car to make the lock-up work. So.... thanks for the info Houston. I'll get my buddie in Va. to pick the parts up for me and mail them over! BTW have you noticed a difference in gas mileage since you fitted it?
The collective knowledge of the HAMB never ceases to amaze me! When I was working as an engineer for GM, I once talked to an older engineer who worked on the development of the original T-350. He was telling me that there was a big internal push from his team to design it with the pump in the center, and the forward drum all the way in the front. That way, a single band could have been used to lock up the converter once it shifted into 2nd. Everyone agreed it was a good idea, but the bean counters didn't want to spend the extra $$$ to develop it. In the end, the management decided it would be better if it's design followed the T-400's design so it would fit within existing patents and copyrights. Also, because they didn't want to have to re-educate tech's to work on a new design. Since they were already trained on the 400, designing the 350 the same way seemed the logical way to go. I started working there in 1985.... So to my defense, I had nothing to do with the disasterous engineering mistakes of those who came before me. I was in engine development, and a lot of my handywork can be found in the 3800 series II, the Northstar, and the LS chevy.... Stuff I'm very proud of.
I thought I had a TH350C...it started acting up...rebuilder says nope....it's a TH250C....not enough guts for a sbc....replaced it with a TH350C rebuilt w/ shift kit....I used a B&M lockup kit which is exactly what the author here avoided. But I like the kit as it allows me to dial-in what mph I want the lockup to engage.
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