I see it was new for 1970. What exactly does it do?
Are there any benefits?
Are there any drawbacks to removing it?
Are there any benefits?
Are there any drawbacks to removing it?
Talk to me about TCS or Transmission Controlled Spark
67_LS1
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I have / had it on my 70 Pontiac Catalina vert and I think it was an emissions control thing, especially in the lower gears. Not a performance enhancement used during downshifts - this was my original thinking.
The gas pedal assembly was different in that it had two wires going to it - an orange and a pink, IIRC. I have removed the pedal assembly and the car's entire TH400 transmission to make way for the LS engine swap and 4L60E transmission.
I still have the orange and pink wires and will eventually tuck them away in the dash because I have no use for them now.
Rick
The gas pedal assembly was different in that it had two wires going to it - an orange and a pink, IIRC. I have removed the pedal assembly and the car's entire TH400 transmission to make way for the LS engine swap and 4L60E transmission.
I still have the orange and pink wires and will eventually tuck them away in the dash because I have no use for them now.
Rick
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It was one of the early day emission functions. With a 4sp, there is a switch on the 4th gear position of the side cover which provides 12v to the solenoid. In turn, the solenoid opens a vacuum passage to the vacuum advance of the distributor, allowing the vacuum of the distributor to function. MOST people (I'm included) either disable the solenoid or deposit it in the trash can and run a "regular" vacuum advance using a manifold vacuum source.
Since auto trannys are against my religion, I cannot expand on how it was connected to an auto.
Since auto trannys are against my religion, I cannot expand on how it was connected to an auto.
No problem with removing it. Connect your vacuum advance to the proper port on the carb, connect the vacuum line to the trans to a port on the Vacuum Tree
Mine is an automatic and there was no connection from the Atascadero to the transmission. 2 different post on the cab, one manifold and the other ported and the other end to the distributor.
There is a vacuum line that goes to the transmission but not from this valve. A hose goes straight from a port in the intake manifold to the transmission.
As long as the manifold vacuum tree is connected to the transmission modulator valve and vac pot connected to the correct carb port the rest can be pulled
my trans is a TH350
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You have the basic idea, but your info isn't correct Tom.
The transmission mounted switch, whether automatic or manual is normally closed, meaning it provides ground on the black "signal wire" until the transmission reaches "high gear" (there are few exceptions on the automatics based on the fluid passage designs).
Once the transmission is shifted into high gear, the ground is lost, thus the solenoid mounted on the manifold loses power, the internal plunger retracts and full vacuum to the vacuum advance on distributor is allowed.
The solenoid in 1970 allows full vacuum to the vacuum advance when there is NO power applied.
The firewall mounted relay provides a cold engine override in which the +12 volt side of solenoid is disconnected when temperature switch provides a ground signal to the relay.
I am one of the few members here who can explain how all 3 years (1970, 1971 and 1972) of the first electronic emissions control systems work. All three years are different, and I have caught many service manuals and website discussions with wrong information.
Most people remove the system. I always warn people though, if they live in jurisdiction that requires original "smog" equipment in place, and testing, then they have to deal with that.
The system retarded the spark, until "high gear" was reached, (so driveability would not overly suffer), thus raising the combustion temperatures and ultimately "burning" of combustion by-products was still occurring as the exhaust valves open. This reduced nitrogen oxides and hydrocarbon emissions out of the tail pipe.
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Here's something that was mailed to us in 1970 from GM, since dad bought a Chevrolet in 1970. I'm glad I saved it.
![Image]()
I also remember seeing a big version of this as a poster on the wall in the service bay at Wills Motors Chevrolet-Oldsmobile at that time.
I also remember seeing a big version of this as a poster on the wall in the service bay at Wills Motors Chevrolet-Oldsmobile at that time.
1971 El Camino SS - 350 4BBL, TH350, AC, PB, PS, 12-bolt Posi (work in progress)
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Wow, this is great Cam. Thanks for sharing.Here's something that was mailed to us in 1970 from GM, since dad bought a Chevrolet in 1970. I'm glad I saved it.
![Image]()
I also remember seeing a big version of this as a poster on the wall in the service bay at Wills Motors Chevrolet-Oldsmobile at that time.
Keep the canister hooked up to control fuel smell. It also adds a little pressure on the vapor line. I’ve had fuel come running out on a steep hill when the nose was pointed down hill when parked with the canister removed. Its easy enough to put a T on the PCV Line or get a PCV with 2 ports to burn up vapor
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I remember dealing with this on my '70 Nova L78 with TH400. Several times I tried connecting a vacuum line direct to the dist, bypassing the TCS. Back then I didn't know about ported vacuum advance which turns out my car had. With the vacuum line bypassing the TCS it made the distributor vacuum can too sensitive. In neutral or park with the idle speed at normal rpm, in gear rpm was too low. With idle speed adjusted to proper rpm in gear it was too high in neutral or park. Now I know it needed for bypassing the TCS either full manifold vacuum, a different dist vacuum can, or both.
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