1974 TCS Configuration

[Paul L.]

Re: 1974 TCS Configuration

Thanks Robert. The diagram I posted above does refer to a Thermo-Override system. The temp sensor between cyls #6 and 8 must control ported vrs manifold vacuum based on internal thermal/heat conditions. I'll try the three hose setup when I see my car again in April.

[Michael W.]

Re: 1974 TCS Configuration

I know function doesn't count, but do you know if the complete electrical system is intact?

[Paul L.]

Re: 1974 TCS Configuration

Yes, the wiring is all there tucked neatly away by me. Remarkably no one has ever hacked on this car. The TCS was in place when I bought the car in 2008 but I removed it to go with manifold vacuum.

[John H.]

Re: 1974 TCS Configuration

The Service Manual says that automatic transmission Corvettes use a Thermo-Override system. The Service Manual does not discuss, at all, how the Thermo-Override system is intended to work and provides no troubleshooting information.

Robert -

Someone who knows more about the gory detail of the override system than I do will probably chime in, but as I recall, it worked like this:

If the engine was cold, the sensor triggered the valve so the distributor got manifold vacuum regardless of gear position until it reached a given temperature.

If the engine was overheating, the sensor triggered the valve so the distributor got manifold vacuum regardless of gear position until it cooled down to "normal" temperature.

When in "normal" temperature range, gear position (high gear) triggered the valve for manifold vacuum; lower gears triggered it for "ported" vacuum.

Or something like that.

[Paul L.]

Re: 1974 TCS Configuration

Robert -

Someone who knows more about the gory detail of the override system than I do will probably chime in, but as I recall, it worked like this:

If the engine was cold, the sensor triggered the valve so the distributor got manifold vacuum regardless of gear position until it reached a given temperature.

If the engine was overheating, the sensor triggered the valve so the distributor got manifold vacuum regardless of gear position until it cooled down to "normal" temperature.

When in "normal" temperature range, gear position (high gear) triggered the valve for manifold vacuum; lower gears triggered it for "ported" vacuum.

Or something like that.

A good argument for just using manifold vacuum as Duke recommends...recommends..and recommends. And it works! But there is the smog police visuals.

[Michael W.]

Re: 1974 TCS Configuration

But there is the smog police visuals.

Mebbe I should rethink my 'Let's move to Ontario! plan'.......

[Paul L.]

Re: 1974 TCS Configuration

You have to assume they know what they are looking at. Not funny Mike.

[Paul L.]

Re: 1974 TCS Configuration

This is the #1997425 unit that I will try. From PartsLadi In Florida.

[William C.]

Re: 1974 TCS Configuration

What you are looking at is an electrically operated vacuum solinoid, the coil(the wound wires) when activated, cause the metal pintle to retract, allowing vacuum to flow to the ports. When the coil is denergized, the spring closes the port.

[Patrick H.]

Re: 1974 TCS Configuration

Lyle,

I have to disagree. The bracket just mounts to the intake manifold bolt whether four-speed or automatic. And the bracket in integral to the "innards". I'll pull my old one apart and we can see what is inside. I'll post pics.

This subject is taking on a life of its own.

*Edit* - These are the innards of a 1974 TCS solenoid for a SB TH400. I have no idea what I am looking at.

I'm with Lyle. There are some solenoids that differ ONLY in the orientation of the bracket. If you reverse the bracket, you get the other part number, and that number is even stamped on the other side.

FYI I've taken a few of these apart previously but never yanked out the wires quite that far. They are usually "fixable" but not anymore...

[Paul L.]

Re: 1974 TCS Configuration

I'm with Lyle. There are some solenoids that differ ONLY in the orientation of the bracket. If you reverse the bracket, you get the other part number, and that number is even stamped on the other side.

FYI I've taken a few of these apart previously but never yanked out the wires quite that far. They are usually "fixable" but not anymore...

Why fool about, just replace it.

[Michael W.]

Re: 1974 TCS Configuration

I'm with Lyle. There are some solenoids that differ ONLY in the orientation of the bracket. If you reverse the bracket, you get the other part number, and that number is even stamped on the other side..

Pat- have you ever seen a solenoid with three ports like this one? I'm familiar only with the two port version.

[Terry M.]

Re: 1974 TCS Configuration

My 1970 has three ports, as do most of the TCS solenoids I am familiar with -- which are those up to 1972. In fact this is the first one I have seen with two ports. Maybe the two port is a "newer" feature.

[Michael W.]

Re: 1974 TCS Configuration

Terry,

What did the third port connect to?

[Patrick H.]

Re: 1974 TCS Configuration

Terry,

What did the third port connect to?

Depends on the application.

Note on mine that the rear port happens to have a foam filter on it, but I have seen it connect to a hose, and the filter on a different port, in different applications.