What is TCS SOL and TCS RELAY on 70BB? - Chevelle Tech
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post #1 of 8 (permalink) Old Oct 3rd, 98, 5:43 PM Thread Starter
Join Date: Sep 1998
Location: Stillman Valley, IL. USA
Posts: 6
Car is a 70 454 SS Convertible with A/C.

I'm installing all-new wiring harnesses on my 70 BB which came without any wiring. According to the 70 GM assembly manual, some of the wires are supposed to connect to the "TCS SOL" and "TCS RELAY". Problem is I don't know where or what these are. My question is, What are they and where are they located?

Also, the wiring harness has provisions for temperature switchs on both sides of the engine. On the driver's side, I have a single green wire with the tar paper surrounding it like on my 71 BB hardtop. On the passenger side, there is another green wire that has a split 90 degree connector which seems to be correct according to the factory assembly manual. Question is, which side is the CORRECT side to mount the temperature sending switch on and what should I do with the other wire?

Purchased all wiring from Year One if that helps.

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post #2 of 8 (permalink) Old Oct 3rd, 98, 6:31 PM
Join Date: Aug 1998
Location: Jackson, Ohio
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First a pat on the back for doing it the right way!!! The TCS sys. is Transmission Controlled Spark. This allows the vacuum advance to be retarded most of the time and to advance when in fourth or high gear. The solenoid is a vacuum switch that bolts to the intake manifold near the back of the carb. It would have a vacuum hose into and out of an extension from a round electrical operator. The manual transmissions had a switch (relay?) on the side that hooked to the shifter arms. The auto trans I assume had a relay internally. Some of these I think had a high temperature override. The temperature gauge wiring on a small block is the single green wire on the driver's side. I'm not up on the big block and that may use the double wire on the pass side. tom
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post #3 of 8 (permalink) Old Oct 3rd, 98, 6:41 PM
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I believe I can help. TCS=transmission controlled spark. This was a 1970 Emissions idea that was really B.S., the whole idea was give the engine advanced timing (via vacuum advance to the distributor) when it was only really needed, therefore reducing exhaust emissions. I spent a lot of time figuring mine out on my 70 chevelle 307--call me Mr. TCS , they're all the same:
The TCS relay is a small relay box that is riveted to the wiring gutter that runs under the hood close to the top of the cowl, you know the one that carries the wire with fuse to the a/c/heater blower.

The TCS solenoid (sol) mounts on the passenger side of the intake manifold by the distributor. It is matallic colored and has 3 nozzles. One goes to the carb base (vacuum)
one goes to the distributor vacuum advance nipple, one goes to the top of the carb (clean air, no vacuum).
A wire runs from your tranny to the relay.

The theory: (I feel like I'm a GM tech spokemans

When the car is in any gear but drive, the small switch that is in the side of the tranny is not activated (not grounded), when you put the car in drive ( i guess 3rd or 4th with a stick shift) the tranny fluid puts pressure on the switch activating it and grounding the circuit that goes to the relay, this causes another circuit to trip that sends 12 volts via the blue and black wire with flat plug to the solenoid on the manifold. So what's that do? It triggers it to let full vacuum from the carb to the vacuum advance on the distributor. The relay is there for "those darn freezing Nebraska winter morning start-ups" Just kidding it is actually for cold starts when you need full advance for the distributer, What knows if it is cold out?

This is the Next part of your question!
The green wire that "splits" into two with a 90 degree plug angle goes to the twin-blade temperature sender on the passenger side of the block, this is what tells the relay that "hey it's cold out!" and turns on the solenoid even if the tranny is not in drive.

As for the tar paper covered green wire--this goes on the driver's side of the block, this is the TRUE temperature sender that tells you if something is wrong with your engine, i.e. makes the Hot light come on or guage move.

I sure hope this helps, are you confused yet, my fingers have writer's cramp!
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post #4 of 8 (permalink) Old Oct 4th, 98, 9:37 AM Thread Starter
Join Date: Sep 1998
Location: Stillman Valley, IL. USA
Posts: 6
Thanks for both of your answers. I now know what they are, what they're used for and how to hook them up.....now if I could jist FIND out what I did with the TCS SOL and RELAY parts.

Thanks again!!!
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post #5 of 8 (permalink) Old Oct 6th, 98, 1:14 PM
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Join Date: Aug 1998
Location: DC Metro Area
Posts: 255

An original GM relay is still availibe through Year One, OPG, or many other m/o houses. I haven't seen a solenoid for sale commerically until recently.

I believe you can get reproduction TCS solenoids from Ground Up:

p/n year/motor price
1114432 1970 - up, all SB $79.99 ea
1114434 1970-71, all BB $79.99 ea
1114453 1972 - up, all BB $79.99 ea

Ground Up - Pristine Motors
p.o. Box 3402
New Hyde Park, NY 11040
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post #6 of 8 (permalink) Old Oct 6th, 98, 1:20 PM
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Location: DC Metro Area
Posts: 255
I've played with the idea of installing this item. What benefits are there to re-installing this system. Will it hurt performance?

I'm not after a hardcore resto nor am I after a monster street sweeper. Just a nice cruiser. My 402 runs very nicely (no complaints) with the vacuum advance running directly from the carb to the distributor.

Any thoughts?
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post #7 of 8 (permalink) Old Oct 6th, 98, 2:09 PM
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michael j: If you just want a good cruiser then don't do it, there is no advantage. It will only hurt performance a little but it definately does not help. To correctly hook it all up and FIND all the correct parts would be a major effort.
By the way the TCS temp sensor that has two lugs on it: one is for low temp and one is for high. Like Coppertop stated this overides the solenoid when its "COLD"(<85deg) and also when "HOT" (>220deg).
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post #8 of 8 (permalink) Old Oct 7th, 98, 6:31 AM
Join Date: Aug 1998
Location: Jackson, Ohio
Posts: 10
Michealj; This system was one of GMs typical stop-gap, Rube Goldberg deals to meet pollution laws back then. I had a couple cars with this and usually removed it about the second day I had it. Only advantage I can see is the timing retard makes the engine idle a little "meaner" with a big cam. The best vacuuum set up is to use ported vacuum with the connection above the throttle plates which will give advance when the throttle is opened partially. If you have cooling problems in town the manifold vacuum might be the best with full time advance except at wide open throttle. tom
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