TCS 1970

[Tony H.]

So there I am in Boston and my car is getting Opertions done. The car si idling at about 750-800 rpm. The ops judge asks me to put my 4spd in third and then fourth gears to check the operation of the TCS. Rpm should jump to around 1100 rpm but instead nothing happens. So I fail that part. On my way to home two days later, I notice that the oil level is low (2 quarts low). Today I change the oil and filter. When I start the car to circulate the new oil, I test the TCS and it works just fine: 1100 rpm when in 3rd or 4th gears.

Can someone tell me under what conditions TCS should kick in? Might the low oil level have caused temperatures to get hot enough to prevent TCS from working during the ops check? Or might there just not been enough vacuum to overcome the high friction condition of low oil? Or both?

Thanks for any help.

Tony

[Bill Clupper]

Re: TCS 1970

Tony, I don't have a full info package for '70, but in some years, (72) there was a 20 second delay built in if the system was shifted between gears also, a temp switch is used, full vacuum is avaiolable on an averride basis if temp is below 82 degrees or over 252. Highly unlikely that you had a temp that high.

[Bill Clupper]

Re: TCS 1970

Tony, I don't have a full info package for '70, but in some years, (72) there was a 20 second delay built in if the system was shifted between gears also, a temp switch is used, full vacuum is avaiolable on an averride basis if temp is below 82 degrees or over 252. Highly unlikely that you had a temp that high.

[Jack H.]

Re: TCS 1970

TCS theory of operation ought to be covered in the emissions section of '70 CSM even though Corvette is not included since it was delayed for mid-year introduction. Think you'll find TCS consists of the vac relay (open/close vac advance to distributor) mounted on the intake, the control relay (electrical DTL logic package) mounted on the upper firewall, the tranny switch and the RH cylinder head temp switch.

Fuzzy memory tells me input to the TCS control relay comes from tranny switch (what gear we in now, boss?) and is tempered by the cylinder head thermal switch (give full vac advance if engine is cold OR entering overheat state). Our Maestro 'd '70, Terry McManmon, could tell the whole story and/or his team's Performance Verification book should also give the story as that's what's being used in lieu of an Operations section in the JG these days.

Bottom line, rise in RPM, I believe, is a simple function of vac or no vac advance to the distributor. In later years, a solenoid mounted to the car actually kicked up curb idle on the carb. Sooo, suggests something went 'bump in the night' to prevent vac from advancing the distributor (flakey vac can on distributor, vac switch malfunction, TCS controller/tranny switch malfunction are all candidates).

If engine was too hot/too cold, thermal switch should have CLOSED and given full time vac advance to distributor overriding balance of system. But, you said low RPM (indicating NO vac advance) was what bit you in Boston and not HIGH revs independent of engine temp/time....

[Jack H.]

Re: TCS 1970

TCS theory of operation ought to be covered in the emissions section of '70 CSM even though Corvette is not included since it was delayed for mid-year introduction. Think you'll find TCS consists of the vac relay (open/close vac advance to distributor) mounted on the intake, the control relay (electrical DTL logic package) mounted on the upper firewall, the tranny switch and the RH cylinder head temp switch.

Fuzzy memory tells me input to the TCS control relay comes from tranny switch (what gear we in now, boss?) and is tempered by the cylinder head thermal switch (give full vac advance if engine is cold OR entering overheat state). Our Maestro 'd '70, Terry McManmon, could tell the whole story and/or his team's Performance Verification book should also give the story as that's what's being used in lieu of an Operations section in the JG these days.

Bottom line, rise in RPM, I believe, is a simple function of vac or no vac advance to the distributor. In later years, a solenoid mounted to the car actually kicked up curb idle on the carb. Sooo, suggests something went 'bump in the night' to prevent vac from advancing the distributor (flakey vac can on distributor, vac switch malfunction, TCS controller/tranny switch malfunction are all candidates).

If engine was too hot/too cold, thermal switch should have CLOSED and given full time vac advance to distributor overriding balance of system. But, you said low RPM (indicating NO vac advance) was what bit you in Boston and not HIGH revs independent of engine temp/time....

[Trebor]

Re: TCS 1970

The TSC is actuated by a switch on the trans. This triggers a solenoid on the intake that opens the vacuum to the distributor's advance system when shifted in 4th or 3rd gear. Oil level in engine or trans will not hinder operation. Your car must be a late 70 because my early L-46 car did not have system. There should not be a delaying device used in your car. The switch on trans is located on the shift lever cover. As far as system not working start with the wiring then check the vac. adv. on distributor. Sometimes the solenoid on the intake will stick. I have only owned 1 car with this system and that was a 1971 LT-1 which should be the same..

[Trebor]

Re: TCS 1970

The TSC is actuated by a switch on the trans. This triggers a solenoid on the intake that opens the vacuum to the distributor's advance system when shifted in 4th or 3rd gear. Oil level in engine or trans will not hinder operation. Your car must be a late 70 because my early L-46 car did not have system. There should not be a delaying device used in your car. The switch on trans is located on the shift lever cover. As far as system not working start with the wiring then check the vac. adv. on distributor. Sometimes the solenoid on the intake will stick. I have only owned 1 car with this system and that was a 1971 LT-1 which should be the same..

[Terry M.]

Re: TCS 1970

Tony,

I w2ould have to look it all up in the PV manual, but Off the top of my head I do not think there is a time delay for TCS for your 1970 LS5. Could a vacuum line have been disconnected or the vacuum advance unit sticky??

Terry

[Terry M.]

Re: TCS 1970

Tony,

I w2ould have to look it all up in the PV manual, but Off the top of my head I do not think there is a time delay for TCS for your 1970 LS5. Could a vacuum line have been disconnected or the vacuum advance unit sticky??

Terry

[Tony H.]

Re: TCS 1970 - Resolved

I found the problem. Today I started up my 70 LS5 (late production, July 20, 1970) and I played with the connection at the TCS solenoid. When I would push in the wires in at the solenoid terminals, the engine speed would periodically increase (as expected under cold start condition). The connector appeared to be good so I removed the solenoid. I dismantled the solenoid and removed the plastic piece with the windings and found that one of the leads (the outer one) to the windings had broken off. So, I unwound that lead wire one complete revolution and that gave me about three inches of wire to connect to the terminal. Voila. After I connected the new wire lead to the terminal, good as new. Apparently, this break in the winding created an intermittent condition with the TCS during the operations check and this morning. Thanks for the help.

Tony

[Tony H.]

Re: TCS 1970 - Resolved

I found the problem. Today I started up my 70 LS5 (late production, July 20, 1970) and I played with the connection at the TCS solenoid. When I would push in the wires in at the solenoid terminals, the engine speed would periodically increase (as expected under cold start condition). The connector appeared to be good so I removed the solenoid. I dismantled the solenoid and removed the plastic piece with the windings and found that one of the leads (the outer one) to the windings had broken off. So, I unwound that lead wire one complete revolution and that gave me about three inches of wire to connect to the terminal. Voila. After I connected the new wire lead to the terminal, good as new. Apparently, this break in the winding created an intermittent condition with the TCS during the operations check and this morning. Thanks for the help.

Tony

[Jack H.]

Re: TCS 1970

'71 was QUITE different. That was a Corvette one year only 'wonder' called CEC (combined emissions control). Inputs to the system were the same as '70's TCS (switch on tranny and temp switch in RH cyl head) but control logic was very different, DID include various time delay features, and used carb mounted solenoid that provided dual functions (engage/defeat vac advance to distributor AND boost/drop curb idle RPM).

Also, function of TCS/CEC had modest differences based on whether or not the car was Auto/Manual tranny equipped. So, comparing '70 to '71 is sort of apples & oranges IF we're talking full factory concours stock.

[Jack H.]

Re: TCS 1970

'71 was QUITE different. That was a Corvette one year only 'wonder' called CEC (combined emissions control). Inputs to the system were the same as '70's TCS (switch on tranny and temp switch in RH cyl head) but control logic was very different, DID include various time delay features, and used carb mounted solenoid that provided dual functions (engage/defeat vac advance to distributor AND boost/drop curb idle RPM).

Also, function of TCS/CEC had modest differences based on whether or not the car was Auto/Manual tranny equipped. So, comparing '70 to '71 is sort of apples & oranges IF we're talking full factory concours stock.