TH350C - How to Set Up the Lockup - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Houston54 · 03-27-2009, 10:57 AM

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.

**clay68c10** · 03-28-2009, 01:27 PM

I bet this would work for a 700R4. Anyone know if it will?

*C-10 simplex* · 04-20-2009, 11:34 PM

Can the trans be run without the lockup feature without damaging the transmission?

Houston54 · 04-21-2009, 02:02 PM

Yes it can.

*C-10 simplex* · 04-22-2009, 10:08 AM

Also, i know that the computer(or something) will lock it up (mine is an 83 1/2 ton) and when you press the brakes it will unlock.

What i'm wondering what the vacuum thing is for----which i partially understand will unlock it upon deceleration. Why is this nessesary(if it all)?

The reason why i'm asking is i will have to swap motors (long, sad story why--another topic) and the "new" motor has a different manifold with less/different/non-original vacuum line patterns.

Lugnut64052 · 04-24-2009, 02:18 AM

Quote:

Originally Posted by clay68c10

I bet this would work for a 700R4. Anyone know if it will?

Pretty sure it will. I believe you could use the same setup to lockup a 700R4, a 200-4R or a 350.

Houston 54, thanks for the Delco part numbers. Sure simplifies things.

71Farmtruck · 05-09-2009, 03:58 PM

http://www.73-87.com/7387garage/drivetrain/lockup.htm

03-27-2009, 10:57 AM	#1
Houston54 Registered User Join Date: Feb 2005 Location: location Posts: 527	TH350C - How to Set Up the Lockup 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. Last edited by Houston54; 03-27-2009 at 01:12 PM. Reason: Added current parts pricing

03-28-2009, 01:27 PM	#2
clay68c10 Senior Member Join Date: Aug 2004 Location: Centennial, CO Posts: 2,987	Re: TH350C - How to Set Up the Lockup I bet this would work for a 700R4. Anyone know if it will? __________________ ClusterTruck: 68 C10 Bought in 89, wrecked in 03. Slow low $ rebuild started '17. 6.0 & TKO http://67-72chevytrucks.com/vboard/s...d.php?t=788602 93 K1500 Short Step, 350, NV4500, EBL flash ECU. Vortec heads & roller cam someday... 05 Jeep Wrangler Unlimited. 3” lift & 6-speed 02 E320 the insurance total “free car” 13 Tahoe LTZ

04-20-2009, 11:34 PM	#3
C-10 simplex Account Suspended Join Date: Dec 2008 Location: indisclosed Posts: 1,515	Re: TH350C - How to Set Up the Lockup Can the trans be run without the lockup feature without damaging the transmission?

04-21-2009, 02:02 PM	#4
Houston54 Registered User Join Date: Feb 2005 Location: location Posts: 527	Re: TH350C - How to Set Up the Lockup Yes it can.

04-22-2009, 10:08 AM	#5
C-10 simplex Account Suspended Join Date: Dec 2008 Location: indisclosed Posts: 1,515	Re: TH350C - How to Set Up the Lockup Also, i know that the computer(or something) will lock it up (mine is an 83 1/2 ton) and when you press the brakes it will unlock. What i'm wondering what the vacuum thing is for----which i partially understand will unlock it upon deceleration. Why is this nessesary(if it all)? The reason why i'm asking is i will have to swap motors (long, sad story why--another topic) and the "new" motor has a different manifold with less/different/non-original vacuum line patterns.

05-09-2009, 03:58 PM	#7
71Farmtruck Junk Junkie Join Date: Oct 2007 Location: Humble, TX Posts: 123	Re: TH350C - How to Set Up the Lockup http://www.73-87.com/7387garage/drivetrain/lockup.htm __________________ Mike 71 Chevrolet C-10 Short Bed Stepside 81 GMC 1500 Sierra Classic Long Bed



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