70 SB TCS 4-Speed Trans. Switch

[William C.]

Re: 70 SB TCS 4-Speed Trans. Switch

Not that I can find in the AIM, but I will admit it's not something I have looked at a lot. I know my 72-454 did not have any relay when I pv'd it about 10 or so years ago...

[Terry M.]

Re: 70 SB TCS 4-Speed Trans. Switch

One has to check the PV and Operations manual for the delay list. I sweated over that with the FSMs for the respective years -- and there is no way I am going to try to remember any of that. I am fairly sure 1970 Small Block has no delay, but after that it is all down hill. Bill, some years (1970-1972) with large motor have a delay built into the circuit.

Pat check the AIM for a washer between the stitch and the side cover. I would bet if you add that washer your system will work find. That was what I found, but that was back in the day when I could go to the Chevrolet dealer and buy the washer. I doubt that is the case today, but a copper washer -- like is used on brake systems -- will work just fine.

The date on the washer is April and I suspect our early cars need the washer to work properly.

[Pat M.]

Re: 70 SB TCS 4-Speed Trans. Switch

Well, I'm embarrassed to admit it but it was a dirty/slightly loose positive connection to the solenoid. But what led me there is mildly interesting.

I decided to test the system with the motor off, since you can normally heard the "click" of the solenoid de-energizing. But first I had to disconnect the temp override so it would not constantly read "cold" and disallow de-energization.

I then took Jim's suggestion one step further and connected a test light between the trans switch and the switch wiring. It worked great, lighting up in the low gears showing energization, and going out in 3rd and 4th showing the broken ground and de-energization, which would normally allow vacuum advance. So the switch is not bad, yet I still didn't hear the telltale "click."

So I re-tested the solenoid manually and it worked perfectly. I then used the test light on the solenoid plug and both negative and positive seemed to work. Yet I noticed the positive plug had a relatively large gap and would not hold the solenoid blade firmly. It was also slightly corroded in this same area, and if I touched it gently the test light showed no juice. So I cleaned up the plug, slightly re-crimped it, and the system works perfectly, repeatedly de-energizing in 3rd and 4th gear.

Thanks everyone for their help. And Terry - I didn't check my AIM, but I still think I'll pass on the washer!

[Terry M.]

Re: 70 SB TCS 4-Speed Trans. Switch

Well after your good troubleshooting -- either you have the washer or don't need it. That's fine because I anticipated the next request would be for some dimensions, and there is no way I can get to that part of the car to comply. So I'm happy. And your car works -- so you're happy.
Now all we need is some nice weather to go driving.

[Pat M.]

Re: 70 SB TCS 4-Speed Trans. Switch

Well after your good troubleshooting -- either you have the washer or don't need it. That's fine because I anticipated the next request would be for some dimensions, and there is no way I can get to that part of the car to comply. So I'm happy. And your car works -- so you're happy.Now all we need is some nice weather to go driving.

I do appreciate your input Terry. And the weather here in south Louisiana is perfect - 68 degrees, climbing to mid-70s, cool and clear. That means one of my babies is hittin' the road!

[Terry M.]

Re: 70 SB TCS 4-Speed Trans. Switch

Enjoy. I hit the road to North Carolina Wednesday. The weather forecast is for us to dry out by then, Unfortunately I will be the passenger in my own car. It is, however, the next best thing to driving the Corvette.

[Thad L.]

Re: 70 SB TCS 4-Speed Trans. Switch

Pat , I have an NOS switch and relay. Your welcome to try them to figure out the trouble. Thad
call me at the shop!