1972 vs 1973 TCS

[Christopher K.]

So it looks to me like there is no 20 second delay in advance when shifting to 4th in 1973? Thoughts and comments welcome.

[Edward J.]

Re: 1972 vs 1973 TCS

Chris looks like the grounding path for the delay relay is different than 72. Pretty much the same operation.

[John S.]

Re: 1972 vs 1973 TCS

Christopher, no input from my end on the 72 side of the question but I did confirm that my L82 4 speed has no delay when the trans is shifted into 4th gear. When fully warmed up and idling, the RPM rises approx 400-500 when shifted into 4th gear.

[Christopher K.]

Re: 1972 vs 1973 TCS

Chris looks like the grounding path for the delay relay is different than 72. Pretty much the same operation.

Thanks Ed, it is very similar but it does have some differences. I believe since the TCS delay solenoid has its own ground (which also grounds the blower, anti-theft, and wiper) it creates 2 circuits. The ignition can also go directly to the transmission ground when shifting to 4th gear with no delay as described in the chassis manual.

[Christopher K.]

Re: 1972 vs 1973 TCS

Christopher, no input from my end on the 72 side of the question but I did confirm that my L82 4 speed has no delay when the trans is shifted into 4th gear. When fully warmed up and idling, the RPM rises approx 400-500 when shifted into 4th gear.

John, thanks very much for that ops check, mine operates exactly the same. I even changed out the TCS relay, GM 6270698, with another NOS relay. Same result with both, no vacuum advance delay when shifting to 4th gear and rpm increases 400-500.

[Russ S.]

Re: 1972 vs 1973 TCS

John, I checked out my 73 L82 4 spd today for Chris and found the same thing as you did. No delay.

Christopher, no input from my end on the 72 side of the question but I did confirm that my L82 4 speed has no delay when the trans is shifted into 4th gear. When fully warmed up and idling, the RPM rises approx 400-500 when shifted into 4th gear.

[Gary C.]

Re: 1972 vs 1973 TCS

Chris, just curious but the 73 circuitry appears to shows that the time relay delay happens after shifting out of 4th gear, not happen going into 4th gear. With the 73 manual, the text between your blue highlighted and red highlighted identifies that in "low gear operation with engine temp above 93 deg, the temperature switch cold override points open (Fig 4e). If 20 seconds have elapsed the time relay points are also open. This breaks the circuit(s) de-energizing the vacuum advance solenoid" Thus, if you shift into 4th gear, the time relay points are open and would not cause a delay on shifting into 4th gear (due to wiring circuitry) but looks like the time relay would close given enough time to heat the relay internal coil. Then after (say 1 minute), shift out of 4th gear, does the time relay hold energized the vacuum advance solenoid then cools off after 20 seconds and then de-energizes the vacuum advance solenoid similar to the event with the temperature switch cold override. Would be nice to see Fig. 5e from your manual.
Thanks,
Gary

[Christopher K.]

Re: 1972 vs 1973 TCS

Gary,
First of all thanks for the reply, it’s great to get fresh ideas on this system. My background is in in aviation so I’ve looked at a lot of wiring diagrams but I’m not a EE. My understanding of the system was that initially after start the normally closed timing delay points open after 20 seconds and stay open. That circuit stays complete (points open) with its own ground until shutdown.
When the car is shifted to 4th, another circuit is completed from ignition to vac advance solenoid to trans ground. Vac advance solenoid is energized with no delay.
But I’m certainly willing to try your theory. I won’t be home with the car until next week but I’ll let you know.
Thanks,

[Gary C.]

Re: 1972 vs 1973 TCS

Chris, ok. Looks like the function of time relay is mainly when you start the engine with the engine temperatures between 93 deg F and thermal override (hot) and it engages the vacuum advance solenoid (VAS) for 20 seconds then opens and vacuum advance goes to atmosphere. Or the engine is at say 91 deg F, cold temp switch has ground, if engine temp reaches 93 before 20 seconds, then 20 sec time relay keeps ground on VAS until 20 seconds has been reached and releases ground for VAS. Other than these two cases, the time relay does not contribute to any VAS energizing past 20 seconds. The statement between your red and blue highlighted in the manual is correct as individual items are not consecutive. From this, the delay after coming out of 4th gear as I conjectured is invalid.

Now, with an engine temp between 93 deg F and hot, two cases to check time relay: 1) if you turn on ignition & start engine immediately, you will have a 20 sec high idle (VAS energized) ; 2) if you turn on ignition to on and hold for more than 20 sec, then start engine, no high idle since VAS engagement from 20 sec time delay is removed.

Thanks,
Gary

[Gary C.]

Re: 1972 vs 1973 TCS

With both cases starting with a cold (NC - normally closed) time relay.

[Christopher K.]

Re: 1972 vs 1973 TCS

Gary,
I believe everything you stated is correct. So if you take your car to the grocery store, park and go inside....
When you come out and start your car with a warm engine, you will have 20 seconds of full vacuum advance and then you should see the rpm drop off.

[Jimmy P.]

Re: 1972 vs 1973 TCS

Chris & Gary,
Good job on this both of you. I've been following this since the beginning and wanted to double check this with a few other '73 owners as well as my car and there is no noticeable 20 sec or so delay before the engine rpm increases when the transmission is put into 4th gear. The increase in engine speed is nearly instant as you guys pointed out. I was on the 73-74 TIM&JG 3rd edition revision team with Russ and John and we were so focused on correcting that this increase only happened when the transmission was put in just 4th gear and not 3rd and 4th gear as stated incorrectly in the 2nd edition, we never had a discussion about the delay vs no delay issue. It just never came up at the time. I've made a note of this for any future revision updates. Nice to see that you guys and others are using the 73-74 TIM&JG to check things on your car and then when in doubt question and investigate something that your not really sure about...before changing your car to satisfy the manual.

[Christopher K.]