72 questions

[Joe R.]

Two questions for a 72.

1. The jumer harness that goes to the temp switch on the passenger side cylinder head. What is the correct routing?

2. Lower ball joint rivets. What is the installation procedure and is there a special tool needed for that?

Thanks

[Chuck S.]

Re: 72 questions

1. I am not intimately familiar with how the harness was routed in 72, and I have never been able to find this info in the 70 AIM either. The best reference will be to observe an original car at a regional NCRS meet...it's a short harness; the routing can't be too complicated.

2. Corvette ball joints are riveted to the control arms with heavy duty rivets that must be heated and peened in a hydraulic press. To get an authentic appearance for judging purposes (you'll probably only able to get CLOSE on the ball joint configuration), it's better to just send your control arms off to a Corvette specialist like Bair's Corvette in PA and let them give you the best possible result available.

[Joe R.]

Re: 72 questions

Any more input?

Thanks

[Jeremy D.]

Re: 72 questions

I'm not sure about the '72's but my '70 and '71 have the temperature therm. on the DRIVERS side cylinder head, and the wire that goes from the gauge to it is part of the alternator wiring harness. The PASSENGER side is for the TCS switch.....which if I remember right has a green jumper wire that goes from the thermocouple thingy in the head to somewhere.... I think up to the TCS solenoid which is right next to the carb on a manifold stud. I haven't fooled with my '70 or '71 engine compartment in a long time, but I think from there it's routed over the engine/trans down to the trans to a switch (a little brass post) that I think is on the passenger side of the trans. I remember it being a black wire with a boot on it that made the connection....and I've only seen ONE REAL WIRE to that connection...nobody I know repro's that wire. They make the green jumper, but not the one to the trans, that I know of. I'm sure that some of the NCRS members who sleep with 55 years worth of AIM's under their pillows will jump all over this and set ya straight.
Chuck is right on the money....if you want your ball joints riveted on, send your A-arms to Ed over at Bair's or Van Steel or somebody reputable... Get out your wallet, and have them install new RUBBER bushings and the ball joints. Trust me, you'll be time and money ahead, and your supply of Advil will remain in your medicine cabinet.

[Gary S.]

Re: 72 questions

If you will send me an offline email, I will send you a photo of my TCS temperature solenoid wire and its routing. From memory (alwyas a dangerous scenario), The green wire to that temp unit comes out of the large wire bundle that is secured to the firewall. Iirc, it goes straight to the temp bulb, but I will send you a photo of its starting and terminal end.

Gary
72 LT-1

[Jeremy D.]

Re: 72 questions

That's wierd...I always thought that TCS stood for "TRANSMISSION CONTROLLED SPARK" ...at least that's what the tech manual says. All I know is when I unplug the temperature gauge wire that's with my alternator harness from the sensor in the DRIVERS SIDE cylinder head, my temp gauge doesn't work. The PASSENGER side has the Trans Control Spark solenoid, which goes from the vacuum solenoid on the passenger side of the carburetor on an intake manifold stud to....somewhere. But the point is, to my knowledge, the TCS system has NOTHING to do with the temperature of your engine showing on the gauge. If memory serves me right it was designed to back the timing down in 3rd or 4th gear to increase mileage or something.

1970 300-350 Coupe 056.jpg This is the TCS vacuum solenoid on my '70...according to Dobbins' "Fact Book of the 1968-1972 Stingray", pg. 209 shows a '72 base motor with a nearly identical setup.

1970 300-350 Coupe 232.jpg THIS is the temperature gauge wire that is located on the drivers side cylinder head, near the alternator.

1970 300-350 Coupe 233.jpgThis is the green TCS jumper wire located on the PASSENGER cylinder head...I BELIEVE it goes up to the firewall and down over the trans to the switch on the bottom of the trans. I can't get fully under the hood to really look at it, there's another car on a lift directly above this one.....but it doesn't seem to be immediately connected to the vacuum solenoid on the manifold...

[Chuck S.]

Re: 72 questions

That's wierd...I always thought that TCS stood for "TRANSMISSION CONTROLLED SPARK" ...at least that's what the tech manual says. All I know is when I unplug the temperature gauge wire that's with my alternator harness from the sensor in the DRIVERS SIDE cylinder head, my temp gauge doesn't work. The PASSENGER side has the Trans Control Spark solenoid, which goes from the vacuum solenoid on the passenger side of the carburetor on an intake manifold stud to....somewhere. But the point is, to my knowledge, the TCS system has NOTHING to do with the temperature of your engine showing on the gauge. If memory serves me right it was designed to back the timing down in 3rd or 4th gear to increase mileage or something.

[ATTACH]11239[/ATTACH]

Jeremy, I believe Joe was talking about the little jumper harness that goes to the temperature switch in the passenger side head. It appears identical to the temperature sending unit, but this is not a proportional sender that provides a signal for temperature reading, it is a simple on/off switch at some predetermined temperature.

I'm not even going to attempt to explain what happens with that TCS system (Where is Jack Humphrey when you need him? ). At least two electric signals are affecting operation of the TCS solenoid that routes vacuum to the distributor advance: (1) electrical signal from the transmission, and (2) electrice signal from the head temperature switch.

[Roberto L.]

Re: 72 questions

That's wierd...I always thought that TCS stood for "TRANSMISSION CONTROLLED SPARK" ...at least that's what the tech manual says. All I know is when I unplug the temperature gauge wire that's with my alternator harness from the sensor in the DRIVERS SIDE cylinder head, my temp gauge doesn't work. The PASSENGER side has the Trans Control Spark solenoid, which goes from the vacuum solenoid on the passenger side of the carburetor on an intake manifold stud to....somewhere. But the point is, to my knowledge, the TCS system has NOTHING to do with the temperature of your engine showing on the gauge. If memory serves me right it was designed to back the timing down in 3rd or 4th gear to increase mileage or something.

[ATTACH]11239[/ATTACH]

Hello, the TCS works on two variables, gear selection and temperature. Will give full vac at high gears and at low or high temperatures.

On cruise the car will get full vac in 3rd / 4rd for economy, at low gears no vac, for less emissions. When cold or at very high temp. will give full vac.

Best regards

[Jeremy D.]

Re: 72 questions

Cool...look up a few posts, I shot some pix of my '70 base motor 4 spd. All I know is, mine actually works....which is nothing short of a miracle.

[John H.]

Re: 72 questions

The additional sensor/switch in the passenger side head tells the TCS system two things - if the engine hasn't warmed up yet, or if it's overheating; in either case, the system defaults to full manifold vacuum to the distributor until the engine either warms up or cools down.

[Chuck S.]

Re: 72 questions

[ATTACH]11241[/ATTACH]...This is the green TCS jumper wire located on the PASSENGER cylinder head...I BELIEVE it goes up to the firewall and down over the trans to the switch on the bottom of the trans...

You and Gary seem to have pretty much described the routing...the "bundle of wires" that Gary mentions is undoubtably the engine wiring harness that finally ends at the starter.

I expect the "green wire" connects to the engine wiring harness, but it would not go back down to the transmission. The signal from the transmission is from a grounded switch on the 3-4 selector as Roberto said. The signal from the passenger side head is from a grounded switch completely independent of the transmission signal...the two signals provide "EITHER/OR" input to the TCS solenoid. The TCS solenoid harness simply runs alongside the bottom of the RH valve cover in the wiring clip provided.

[Alan S.]

Re: 72 questions

Joe,
On my 71, #6589, the wire was made into a little 'bundle' (like you'd roll an extension cord) and had a narrow, 3/8ths inch, piece of sticky tape around it, to shorten it. The bundle hangs unsupported above the starter.
Regards,
Alan

[Gary S.]

Re: 72 questions

Hello, the TCS works on two variables, gear selection and temperature. Will give full vac at high gears and at low or high temperatures.

On cruise the car will get full vac in 3rd / 4rd for economy, at low gears no vac, for less emissions. When cold or at very high temp. will give full vac.

Best regards

Roberto,
I believe that you can add a third variable in that equation. The TCS relay, on the interior side of the firewall, has a timer on it that must be satisfied, even if temperature and gear selection are good, before the system sees full vacuum. That timer is set nominally at 30 seconds. This is all from memory but I am pretty certain that the number is correct.

In addition, the gear selection only works with fourth gear on 1972s.

Gary

[Roberto L.]

Re: 72 questions

Roberto,
I believe that you can add a third variable in that equation. The TCS relay, on the interior side of the firewall, has a timer on it that must be satisfied, even if temperature and gear selection are good, before the system sees full vacuum. That timer is set nominally at 30 seconds. This is all from memory but I am pretty certain that the number is correct.

In addition, the gear selection only works with fourth gear on 1972s.

Gary

Hello Gary, you are right, I forgot to mention it. In 1970 the TCS relay is in firewall (engine side, Littlefuse).

To illustrate this is my 70 firewall when partially dissasembled, DG and DBL wires connect to the TCS temp switch in RH head.



Correct me, but regarding this post question, the 72 is hidden under interior console.

Best regards