1970's Transmission controlled spark system

[Cadman-iac]

 I'm curious about how well the transmission controlled spark system really worked on these cars. Was it actually helpful,  and was it's purpose just to keep the engine running cooler,  to control emissions,  or something else?
Would you put one in today if you had one available,  and why, or why not? Please elaborate.
  Also,  are all the pieces located in the transmission,  or is there any other controls or whatever inside the car or on the engine itself?
Many thanks for your opinion and knowledge on this.

Rick

(The reason I ask is because I have one still in the transmission that came out of a '70 coupe I parted years ago. I want to know if it's worth messing with).

["Cadillac Kid" Greg Surfas 15364]

Rick
On my 72 Eldo, the TCS was an in-line device (centrifugal switch) in the speedometer outlet of the transmission.  Once the car had reached sufficient speed as judged by the speedometer revolutions the switch would close, activating a solenoid in the vacuum advance circuit, allowing vacuum advance.
Its purpose was to reduce the advance and therefore (hopefully) the Oxides of Nitrogen in the exhaust
Greg Surfas

[TJ Hopland]

I had only seen the inline devices like Greg described on Cadillacs.   On other GM's with manual transmissions they seemed to favor a switch in the trans that activated in high gear. 

[Cadman-iac]

  Thanks Greg,
  I need to check the transmission again to make sure that it does have a 2 wire connector on it, and make sure of the year too. I took one out of a 70, and one from a 72, both coupes, and if I wanted to use the system,  I would have to make sure I have all the pieces.
But mainly I wanted to know if anyone thought it was something worth bothering with.
Since it's not going to be going through any emissions station, obviously I'm not worried about it passing. Other than the emissions side of it, was there any benefit from the system to performance or cooling?

Rick

[Cadillac Fleetwood]

The transmission-controlled spark (TCS ) on a 1970 Cadillac 472 was part electrical, and part vacuum-operated.  There was a vacuum-electric solenoid mounted near the coil.  The system was designed to prevent any vacuum advance until the transmission shifted into third (high) gear.  The theory was that this would reduce emissions of NOX or oxides of nitrogen.  In response to an electrical signal, the solenoid valve would close off vacuum to the vacuum advance unit on the distributor. Compared to a '68 or '69 which did not have TCS,  the '70 lacked a little bit of "oomph" at the low end.  The TCS  was capable of being bypassed, thus allowing vacuum advance in all gear ranges. My 1970 Fleetwood Brougham's TCS was bypassed while leaving everything in place and "apparently" connected and routed as per factory specs. With full vacuum advance, it is not lacking in the lower ranges.

-Charles Fares

[Cadman-iac]

 Thank you Charles,
So is the general consensus that this system is not advantageous to the operation of the engine then?

I don't know why, I think I must be confusing another system with this one.  But I thought I had heard it increased the engine speed to help cooling while in traffic. Is there any such system on a Cadillac?

[Cadillac Fleetwood]

Thank you Charles,
So is the general consensus that this system is not advantageous to the operation of the engine then?

I don't know why, I think I must be confusing another system with this one.  But I thought I had heard it increased the engine speed to help cooling while in traffic. Is there any such system on a Cadillac?

Yes.  1967, 1968, and 1969 models equipped with air conditioning had an idle-speed-up solenoid mounted to the RH rear of the carburetor (passenger side). It was operated by vacuum, and increased the idle speed to 950 rpm in order to prevent overheating in slow-and-go traffic in warm weather with the AC on, by raising the engine speed to promote cooling.  Vacuum from the AC vacuum circuit exerted pull on a diaphragm, which in turn, actuated a lever, manually increasing the idle speed through carburetor linkage. California cars in 1970 used this system. Other 1970 cars used a thermal switch that was actuated by the ported vacuum valve near the distributor. Its operation was directly linked t coolant temperature.

Charles Fares

[The Tassie Devil(le)]

And by changing to full Manifold Vacuum to the Distributor negates it all together.

A lot of these "add-ons" were created in an attempt to appease the Legislators in controlling Pollution output.   Just have to look at California, they started controlling engines back in the early '60's.

Bruce.

[klinebau]

My understanding is that because the '70 did not use an air pump, the TCS was used instead.  The purpose of the TCS was to reduce NOX emissions.  I am not one for removing or bypassing the original equipment, but this is one exception.

[Cadman-iac]

 My thanks to everyone for your input on this subject.  It sounds to me like it's not a system that I want to use. This just clarified it for me. I don't need to make things more complicated than necessary,  and this system will complicate things, so it's a no-go.
And thanks for clearing up my confusion about the other system for increasing engine speed. Not sure how I got the two mixed up.
Thanks again, I appreciate your help.

Rick

[fishnjim]

Artifact of the understanding of the era, turning point of "cheap" gas and rise of environmental awareness.
There was so much "talk" and not much action about air pollution.   The automakers didn't want it(cost), the EPA demanded stuff, and the technology wasn't there.   Still going on to an extent today.   Everytime ones moves an endpoint something has to give.   Now we've even seen "cheating" with the exhaust numbers.   Legislature/legal don't understand technology.   That's why they collect "public comment".
NOx is only favorably produced at temperatures above 1650F.   Below that little(<<1 ppm) or none.
Reason they added water or injected water (now DEF) into diesels.   Lowers the combustion temperature.   Also lowers sooting a bit, also the reason for oxygenates; MBTE, EtOH and low compression.   Catalytic convertors exposed the "quality" of the gas being burned and drove "clean" fuels.   They pretty much proved that pulsed, injection and sparking, and other digital based enhancements are more effective than these "bolt" on solutions to an existing problem vehicle, like smog pumps...   
One reason for the current shift to electrics, ignore the power plant emissions - already controlled, and you don't have to "monitor" every vehicle.   Non-containment areas have/had EPA mandated exhaust gas monitoring for decades now.   Blind sighted approach in my view, huge increase in power plant/solar and resource infrastructure demands. 

Anything that's been "obsoleted" is pretty good proof that was either ineffective or not cost effective than something else.   So going back ward to "original" isn't always the best course.   More for hobby curiosity than not.

[TJ Hopland]

So 71 and or 72 they decided 3rd gear wasn't good enough and went to the speedo sensor method?

[Cadman-iac]

So 71 and or 72 they decided 3rd gear wasn't good enough and went to the speedo sensor method?

After all the comments on this,  I did some research,  which I was able to do after being directed to the correct locations by the aforementioned comments.

What I found was that the 70 has a pressure switch on the valve body in the 3rd gear channel. This is the first picture.

Unfortunately I don't have a manual for the 71 models,  but in the 72's, the pressure switch was eliminated,  and in its place was a speed switch.
For cars with the optional "Track Master" anti-lock  rear brakes,  there is an in-line unit on the speedometer cable itself midway between the transmission and the speedometer.  This is the 2nd picture.

Then for the cars without the anti-lock brake option,  the speed switch is built into the speedometer gear housing on the transmission.
I wondered why there was a wire sticking out of it when I was removing the transmission from the car. This is the 3rd picture.

Again I wish to thank each of you that have replied here and answered my questions. I was not sure if this system would be of any benefit to improving the performance of the engine,  but your replies have opened my eyes,  and I see that it's not worth messing around with.
I really appreciate your input.

Rick