1970 TCS Switch

[Deane M.]

Looking for the correct part number for the transmission side cover switch for the TCS system for my 1970. Also a good source for one.
Thanks.

[Terry M.]

Re: 1970 TCS Switch

The original part number is in the AIM, which I don't have access to at the moment or I would give you the page number. The bad news is I doubt that number will do you any good.

The terminal on that switch for 1970 is a pin connector. 1972 switch has a spade lug, and so is a different part number. Someplace in between the switch and connector changed, so be careful of what you buy.

[Lynn H.]

Re: 1970 TCS Switch

One of my parts books shows the 70-71 switch on trans as being P/N 6462286 (GR-4.075, 2.408) for the turbo 400 and P/N 3961567 (GR-2.408) for the manual trans, if I am reading it correctly.
Lynn

I see the 3961567 in the 70 AIM on page K204 UPC 7 Sheet B6.

[Edward J.]

Re: 1970 TCS Switch

Deane, sometimes those switchs you can disassy. them and clean the contact areas and reassy. is the switch still on the car?

The other thing is check those electrical connectors sometimes the weather gets to them.

[Lynn H.]

Re: 1970 TCS Switch

The original part number is in the AIM, which I don't have access to at the moment or I would give you the page number. The bad news is I doubt that number will do you any good.

The terminal on that switch for 1970 is a pin connector. 1972 switch has a spade lug, and so is a different part number. Someplace in between the switch and connector changed, so be careful of what you buy.

Terry,
In the 70 AIM drawing (4 spd) it appears to be the pin style connector. In the 70 chassis service manual (pg 7-44) it shows the spade terminal connector for the turbo 400. Is it possibly that they were both used in 70 depending on transmission option??
Lynn

[Terry M.]

Re: 1970 TCS Switch

I can't speak to the TH400 style, and I should have made that clear in my post.

I had some intermittent actuation issues on the switch on my 4-speed years ago and found I could cure them with the use of the copper washer under the switch. The early 1970 cars didn't have the copper washer, but later 1970 production did. Years ago one could just go to the dealer and get that washer, but I would be surprised one could do that now days -- unless that washer has some other application.

[Lynn H.]

Re: 1970 TCS Switch

I just had a look at the original turbo 400 out of my 70 convertible, and it does have the spade style connectors. I would also wonder if the switch itself is available?? Possibly, someone else will know and if so and where. Just for the heck of it tomorrow, I will look at my 70 Caddy (which also has TCS) to see if it has the same style of switch.
Lynn

[Terry M.]

Re: 1970 TCS Switch

Lynn does the 1970 TH400 have an external TCS switch? I once had a 1972 Chevelle with TH350 that had an external TCS switch, but I can't recall the style of connector. I seem to remember a thread the other day that spoke to an internal TCS switch on the TH400.

[Edward J.]

Re: 1970 TCS Switch

Terry,my 72 I beleive the switch is on the gear shift under the console for the TCS system when the car is put into rev. that activates the tcs solonoid with a delay of 30 seconds. the switch in the transmisson is for the kick down.

[Douglas L.]

Re: 1970 TCS Switch

This is where I purchased my replacement TCS switch. They are difficult to find.

http://www.thepartsplaceinc.com/ocat...D=10&curpage=3

Scroll down to part #
EL8426Z

[Lynn H.]

Re: 1970 TCS Switch

Lynn does the 1970 TH400 have an external TCS switch? I once had a 1972 Chevelle with TH350 that had an external TCS switch, but I can't recall the style of connector. I seem to remember a thread the other day that spoke to an internal TCS switch on the TH400.

Terry,
It is an internal switch on the 400. I have a picture here. The service manual states the connector that is closest to horizontal is "the pressure terminal", and the vertical one the "detent terminal"
Lynn

[Terry M.]

Re: 1970 TCS Switch

So Lynn what we are seeing on the TH400 is the connector that the chassis wiring harness plugs into -- as opposed to the actual TCS switch. Now that I think about it this looks a lot like what was on the TH400 in my 1976 Suburban.

[Terry M.]

Re: 1970 TCS Switch

Ed the TCS also works in third or high gear with the TH400 so there is more to it than a switch on the gear selector. The TCS switch in the TH400 connects to a line pressure source and when the line pressure is over a certain level the switch closes to ground. The highest line pressure is when the transmission is in reverse and that is why the TCS energizes in reverse and high gear. The reverse actuation serves no purpose in the grand scheme of things except to allow us to more easily check system function. I often have images of the engineers of long ago sitting around a drafting table saying: "We will fool those NCRS guys forty years from now."

Yes one of those wires is for the detent or "kick down" and that signal comes from a micro- switch on the accelerator linkage above the accelerator pedal through that wire in the connector to the solenoid in the TH400 valve body.

[Lynn H.]

Re: 1970 TCS Switch

So Lynn what we are seeing on the TH400 is the connector that the chassis wiring harness plugs into -- as opposed to the actual TCS switch. Now that I think about it this looks a lot like what was on the TH400 in my 1976 Suburban.

I have another THM 400 that I believe may have come from a truck application. It is for the 75 model year (but if I understand the date codes correctly was assembled in early 74). It appears similar, but only has one spade connector on it. Here is a picture of that one.

[Lynn H.]

Re: 1970 TCS Switch

Forgot the picture. This is the 75 THM 400, I believe from a truck.